# Django 5.2 documentation

# Source code for django.db.models.expressions

    import copy
    import datetime
    import functools
    import inspect
    from collections import defaultdict
    from decimal import Decimal
    from enum import Enum
    from itertools import chain
    from types import NoneType
    from uuid import UUID

    from django.core.exceptions import EmptyResultSet, FieldError, FullResultSet
    from django.db import DatabaseError, NotSupportedError, connection
    from django.db.models import fields
    from django.db.models.constants import LOOKUP_SEP
    from django.db.models.query_utils import Q
    from django.utils.deconstruct import deconstructible
    from django.utils.functional import cached_property, classproperty
    from django.utils.hashable import make_hashable

    class SQLiteNumericMixin:
        """
        Some expressions with output_field=DecimalField() must be cast to
        numeric to be properly filtered.
        """

        def as_sqlite(self, compiler, connection, **extra_context):
            sql, params = self.as_sql(compiler, connection, **extra_context)
            try:
                if self.output_field.get_internal_type() == "DecimalField":
                    sql = "(CAST(%s AS NUMERIC))" % sql
            except FieldError:
                pass
            return sql, params

    class Combinable:
        """
        Provide the ability to combine one or two objects with
        some connector. For example F('foo') + F('bar').
        """

        # Arithmetic connectors
        ADD = "+"
        SUB = "-"
        MUL = "*"
        DIV = "/"
        POW = "^"
        # The following is a quoted % operator - it is quoted because it can be
        # used in strings that also have parameter substitution.
        MOD = "%%"

        # Bitwise operators - note that these are generated by .bitand()
        # and .bitor(), the '&' and '|' are reserved for boolean operator
        # usage.
        BITAND = "&"
        BITOR = "|"
        BITLEFTSHIFT = "<<"
        BITRIGHTSHIFT = ">>"
        BITXOR = "#"

        def _combine(self, other, connector, reversed):
            if not hasattr(other, "resolve_expression"):
                # everything must be resolvable to an expression
                other = Value(other)

            if reversed:
                return CombinedExpression(other, connector, self)
            return CombinedExpression(self, connector, other)

        #############
        # OPERATORS #
        #############

        def __neg__(self):
            return self._combine(-1, self.MUL, False)

        def __add__(self, other):
            return self._combine(other, self.ADD, False)

        def __sub__(self, other):
            return self._combine(other, self.SUB, False)

        def __mul__(self, other):
            return self._combine(other, self.MUL, False)

        def __truediv__(self, other):
            return self._combine(other, self.DIV, False)

        def __mod__(self, other):
            return self._combine(other, self.MOD, False)

        def __pow__(self, other):
            return self._combine(other, self.POW, False)

        def __and__(self, other):
            if getattr(self, "conditional", False) and getattr(other, "conditional", False):
                return Q(self) & Q(other)
            raise NotImplementedError(
                "Use .bitand(), .bitor(), and .bitxor() for bitwise logical operations."
            )

        def bitand(self, other):
            return self._combine(other, self.BITAND, False)

        def bitleftshift(self, other):
            return self._combine(other, self.BITLEFTSHIFT, False)

        def bitrightshift(self, other):
            return self._combine(other, self.BITRIGHTSHIFT, False)

        def __xor__(self, other):
            if getattr(self, "conditional", False) and getattr(other, "conditional", False):
                return Q(self) ^ Q(other)
            raise NotImplementedError(
                "Use .bitand(), .bitor(), and .bitxor() for bitwise logical operations."
            )

        def bitxor(self, other):
            return self._combine(other, self.BITXOR, False)

        def __or__(self, other):
            if getattr(self, "conditional", False) and getattr(other, "conditional", False):
                return Q(self) | Q(other)
            raise NotImplementedError(
                "Use .bitand(), .bitor(), and .bitxor() for bitwise logical operations."
            )

        def bitor(self, other):
            return self._combine(other, self.BITOR, False)

        def __radd__(self, other):
            return self._combine(other, self.ADD, True)

        def __rsub__(self, other):
            return self._combine(other, self.SUB, True)

        def __rmul__(self, other):
            return self._combine(other, self.MUL, True)

        def __rtruediv__(self, other):
            return self._combine(other, self.DIV, True)

        def __rmod__(self, other):
            return self._combine(other, self.MOD, True)

        def __rpow__(self, other):
            return self._combine(other, self.POW, True)

        def __rand__(self, other):
            raise NotImplementedError(
                "Use .bitand(), .bitor(), and .bitxor() for bitwise logical operations."
            )

        def __ror__(self, other):
            raise NotImplementedError(
                "Use .bitand(), .bitor(), and .bitxor() for bitwise logical operations."
            )

        def __rxor__(self, other):
            raise NotImplementedError(
                "Use .bitand(), .bitor(), and .bitxor() for bitwise logical operations."
            )

        def __invert__(self):
            return NegatedExpression(self)

    class OutputFieldIsNoneError(FieldError):
        pass

    class BaseExpression:
        """Base class for all query expressions."""

        empty_result_set_value = NotImplemented
        # aggregate specific fields
        is_summary = False
        # Can the expression be used in a WHERE clause?
        filterable = True
        # Can the expression be used as a source expression in Window?
        window_compatible = False
        # Can the expression be used as a database default value?
        allowed_default = False
        # Can the expression be used during a constraint validation?
        constraint_validation_compatible = True
        # Does the expression possibly return more than one row?
        set_returning = False
        # Does the expression allow composite expressions?
        allows_composite_expressions = False

        def __init__(self, output_field=None):
            if output_field is not None:
                self.output_field = output_field

        def __getstate__(self):
            state = self.__dict__.copy()
            state.pop("convert_value", None)
            return state

        def get_db_converters(self, connection):
            return (
                []
                if self.convert_value is self._convert_value_noop
                else [self.convert_value]
            ) + self.output_field.get_db_converters(connection)

        def get_source_expressions(self):
            return []

        def set_source_expressions(self, exprs):
            assert not exprs

        def _parse_expressions(self, *expressions):
            return [
                (
                    arg
                    if hasattr(arg, "resolve_expression")
                    else (F(arg) if isinstance(arg, str) else Value(arg))
                )
                for arg in expressions
            ]

        def as_sql(self, compiler, connection):
            """
            Responsible for returning a (sql, [params]) tuple to be included
            in the current query.

            Different backends can provide their own implementation, by
            providing an `as_{vendor}` method and patching the Expression:

            ```
            def override_as_sql(self, compiler, connection):
                # custom logic
                return super().as_sql(compiler, connection)
            setattr(Expression, 'as_' + connection.vendor, override_as_sql)
            ```

            Arguments:
             * compiler: the query compiler responsible for generating the query.
               Must have a compile method, returning a (sql, [params]) tuple.
               Calling compiler(value) will return a quoted `value`.

             * connection: the database connection used for the current query.

            Return: (sql, params)
              Where `sql` is a string containing ordered sql parameters to be
              replaced with the elements of the list `params`.
            """
            raise NotImplementedError("Subclasses must implement as_sql()")

        @cached_property
        def contains_aggregate(self):
            return any(
                expr and expr.contains_aggregate for expr in self.get_source_expressions()
            )

        @cached_property
        def contains_over_clause(self):
            return any(
                expr and expr.contains_over_clause for expr in self.get_source_expressions()
            )

        @cached_property
        def contains_column_references(self):
            return any(
                expr and expr.contains_column_references
                for expr in self.get_source_expressions()
            )

        @cached_property
        def contains_subquery(self):
            return any(
                expr and (getattr(expr, "subquery", False) or expr.contains_subquery)
                for expr in self.get_source_expressions()
            )

        def resolve_expression(
            self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False
        ):
            """
            Provide the chance to do any preprocessing or validation before being
            added to the query.

            Arguments:
             * query: the backend query implementation
             * allow_joins: boolean allowing or denying use of joins
               in this query
             * reuse: a set of reusable joins for multijoins
             * summarize: a terminal aggregate clause
             * for_save: whether this expression about to be used in a save or update

            Return: an Expression to be added to the query.
            """
            c = self.copy()
            c.is_summary = summarize
            source_expressions = [
                (
                    expr.resolve_expression(query, allow_joins, reuse, summarize)
                    if expr is not None
                    else None
                )
                for expr in c.get_source_expressions()
            ]
            if not self.allows_composite_expressions and any(
                isinstance(expr, ColPairs) for expr in source_expressions
            ):
                raise ValueError(
                    f"{self.__class__.__name__} expression does not support "
                    "composite primary keys."
                )
            c.set_source_expressions(source_expressions)
            return c

        @property
        def conditional(self):
            return isinstance(self.output_field, fields.BooleanField)

        @property
        def field(self):
            return self.output_field

        @cached_property
        def output_field(self):
            """Return the output type of this expressions."""
            output_field = self._resolve_output_field()
            if output_field is None:
                raise OutputFieldIsNoneError(
                    "Cannot resolve expression type, unknown output_field"
                )
            return output_field

        @property
        def _output_field_or_none(self):
            """
            Return the output field of this expression, or None if
            _resolve_output_field() didn't return an output type.
            """
            try:
                return self.output_field
            except OutputFieldIsNoneError:
                return

        def _resolve_output_field(self):
            """
            Attempt to infer the output type of the expression.

            As a guess, if the output fields of all source fields match then simply
            infer the same type here.

            If a source's output field resolves to None, exclude it from this check.
            If all sources are None, then an error is raised higher up the stack in
            the output_field property.
            """
            # This guess is mostly a bad idea, but there is quite a lot of code
            # (especially 3rd party Func subclasses) that depend on it, we'd need a
            # deprecation path to fix it.
            sources_iter = (
                source for source in self.get_source_fields() if source is not None
            )
            for output_field in sources_iter:
                for source in sources_iter:
                    if not isinstance(output_field, source.__class__):
                        raise FieldError(
                            "Expression contains mixed types: %s, %s. You must "
                            "set output_field."
                            % (
                                output_field.__class__.__name__,
                                source.__class__.__name__,
                            )
                        )
                return output_field

        @staticmethod
        def _convert_value_noop(value, expression, connection):
            return value

        @cached_property
        def convert_value(self):
            """
            Expressions provide their own converters because users have the option
            of manually specifying the output_field which may be a different type
            from the one the database returns.
            """
            field = self.output_field
            internal_type = field.get_internal_type()
            if internal_type == "FloatField":
                return lambda value, expression, connection: (
                    None if value is None else float(value)
                )
            elif internal_type.endswith("IntegerField"):
                return lambda value, expression, connection: (
                    None if value is None else int(value)
                )
            elif internal_type == "DecimalField":
                return lambda value, expression, connection: (
                    None if value is None else Decimal(value)
                )
            return self._convert_value_noop

        def get_lookup(self, lookup):
            return self.output_field.get_lookup(lookup)

        def get_transform(self, name):
            return self.output_field.get_transform(name)

        def relabeled_clone(self, change_map):
            clone = self.copy()
            clone.set_source_expressions(
                [
                    e.relabeled_clone(change_map) if e is not None else None
                    for e in self.get_source_expressions()
                ]
            )
            return clone

        def replace_expressions(self, replacements):
            if not replacements:
                return self
            if replacement := replacements.get(self):
                return replacement
            if not (source_expressions := self.get_source_expressions()):
                return self
            clone = self.copy()
            clone.set_source_expressions(
                [
                    expr.replace_expressions(replacements) if expr else None
                    for expr in source_expressions
                ]
            )
            return clone

        def get_refs(self):
            refs = set()
            for expr in self.get_source_expressions():
                if expr is None:
                    continue
                refs |= expr.get_refs()
            return refs

        def copy(self):
            return copy.copy(self)

        def prefix_references(self, prefix):
            clone = self.copy()
            clone.set_source_expressions(
                [
                    (
                        F(f"{prefix}{expr.name}")
                        if isinstance(expr, F)
                        else expr.prefix_references(prefix)
                    )
                    for expr in self.get_source_expressions()
                ]
            )
            return clone

        def get_group_by_cols(self):
            if not self.contains_aggregate:
                return [self]
            cols = []
            for source in self.get_source_expressions():
                cols.extend(source.get_group_by_cols())
            return cols

        def get_source_fields(self):
            """Return the underlying field types used by this aggregate."""
            return [e._output_field_or_none for e in self.get_source_expressions()]

        def asc(self, **kwargs):
            return OrderBy(self, **kwargs)

        def desc(self, **kwargs):
            return OrderBy(self, descending=True, **kwargs)

        def reverse_ordering(self):
            return self

        def flatten(self):
            """
            Recursively yield this expression and all subexpressions, in
            depth-first order.
            """
            yield self
            for expr in self.get_source_expressions():
                if expr:
                    if hasattr(expr, "flatten"):
                        yield from expr.flatten()
                    else:
                        yield expr

        def select_format(self, compiler, sql, params):
            """
            Custom format for select clauses. For example, EXISTS expressions need
            to be wrapped in CASE WHEN on Oracle.
            """
            if hasattr(self.output_field, "select_format"):
                return self.output_field.select_format(compiler, sql, params)
            return sql, params

        def get_expression_for_validation(self):
            # Ignore expressions that cannot be used during a constraint validation.
            if not getattr(self, "constraint_validation_compatible", True):
                try:
                    (expression,) = self.get_source_expressions()
                except ValueError as e:
                    raise ValueError(
                        "Expressions with constraint_validation_compatible set to False "
                        "must have only one source expression."
                    ) from e
                else:
                    return expression
            return self

    @deconstructible
    class Expression(BaseExpression, Combinable):
        """An expression that can be combined with other expressions."""

        @classproperty
        @functools.lru_cache(maxsize=128)
        def _constructor_signature(cls):
            return inspect.signature(cls.__init__)

        @classmethod
        def _identity(cls, value):
            if isinstance(value, tuple):
                return tuple(map(cls._identity, value))
            if isinstance(value, dict):
                return tuple((key, cls._identity(val)) for key, val in value.items())
            if isinstance(value, fields.Field):
                if value.name and value.model:
                    return value.model._meta.label, value.name
                return type(value)
            return make_hashable(value)

        @cached_property
        def identity(self):
            args, kwargs = self._constructor_args
            signature = self._constructor_signature.bind_partial(self, *args, **kwargs)
            signature.apply_defaults()
            arguments = iter(signature.arguments.items())
            next(arguments)
            identity = [self.__class__]
            for arg, value in arguments:
                # If __init__() makes use of *args or **kwargs captures `value`
                # will respectively be a tuple or a dict that must have its
                # constituents unpacked (mainly if contain Field instances).
                value = self._identity(value)
                identity.append((arg, value))
            return tuple(identity)

        def __eq__(self, other):
            if not isinstance(other, Expression):
                return NotImplemented
            return other.identity == self.identity

        def __hash__(self):
            return hash(self.identity)

    # Type inference for CombinedExpression.output_field.
    # Missing items will result in FieldError, by design.
    #
    # The current approach for NULL is based on lowest common denominator behavior
    # i.e. if one of the supported databases is raising an error (rather than
    # return NULL) for `val <op> NULL`, then Django raises FieldError.

    _connector_combinations = [
        # Numeric operations - operands of same type.
        # PositiveIntegerField should take precedence over IntegerField (except
        # subtraction).
        {
            connector: [
                (
                    fields.PositiveIntegerField,
                    fields.PositiveIntegerField,
                    fields.PositiveIntegerField,
                ),
            ]
            for connector in (
                Combinable.ADD,
                Combinable.MUL,
                Combinable.DIV,
                Combinable.MOD,
                Combinable.POW,
            )
        },
        # Other numeric operands.
        {
            connector: [
                (fields.IntegerField, fields.IntegerField, fields.IntegerField),
                (fields.FloatField, fields.FloatField, fields.FloatField),
                (fields.DecimalField, fields.DecimalField, fields.DecimalField),
            ]
            for connector in (
                Combinable.ADD,
                Combinable.SUB,
                Combinable.MUL,
                # Behavior for DIV with integer arguments follows Postgres/SQLite,
                # not MySQL/Oracle.
                Combinable.DIV,
                Combinable.MOD,
                Combinable.POW,
            )
        },
        # Numeric operations - operands of different type.
        {
            connector: [
                (fields.IntegerField, fields.DecimalField, fields.DecimalField),
                (fields.DecimalField, fields.IntegerField, fields.DecimalField),
                (fields.IntegerField, fields.FloatField, fields.FloatField),
                (fields.FloatField, fields.IntegerField, fields.FloatField),
            ]
            for connector in (
                Combinable.ADD,
                Combinable.SUB,
                Combinable.MUL,
                Combinable.DIV,
                Combinable.MOD,
            )
        },
        # Bitwise operators.
        {
            connector: [
                (fields.IntegerField, fields.IntegerField, fields.IntegerField),
            ]
            for connector in (
                Combinable.BITAND,
                Combinable.BITOR,
                Combinable.BITLEFTSHIFT,
                Combinable.BITRIGHTSHIFT,
                Combinable.BITXOR,
            )
        },
        # Numeric with NULL.
        {
            connector: list(
                chain.from_iterable(
                    [(field_type, NoneType, field_type), (NoneType, field_type, field_type)]
                    for field_type in (
                        fields.IntegerField,
                        fields.DecimalField,
                        fields.FloatField,
                    )
                )
            )
            for connector in (
                Combinable.ADD,
                Combinable.SUB,
                Combinable.MUL,
                Combinable.DIV,
                Combinable.MOD,
                Combinable.POW,
            )
        },
        # Date/DateTimeField/DurationField/TimeField.
        {
            Combinable.ADD: [
                # Date/DateTimeField.
                (fields.DateField, fields.DurationField, fields.DateTimeField),
                (fields.DateTimeField, fields.DurationField, fields.DateTimeField),
                (fields.DurationField, fields.DateField, fields.DateTimeField),
                (fields.DurationField, fields.DateTimeField, fields.DateTimeField),
                # DurationField.
                (fields.DurationField, fields.DurationField, fields.DurationField),
                # TimeField.
                (fields.TimeField, fields.DurationField, fields.TimeField),
                (fields.DurationField, fields.TimeField, fields.TimeField),
            ],
        },
        {
            Combinable.SUB: [
                # Date/DateTimeField.
                (fields.DateField, fields.DurationField, fields.DateTimeField),
                (fields.DateTimeField, fields.DurationField, fields.DateTimeField),
                (fields.DateField, fields.DateField, fields.DurationField),
                (fields.DateField, fields.DateTimeField, fields.DurationField),
                (fields.DateTimeField, fields.DateField, fields.DurationField),
                (fields.DateTimeField, fields.DateTimeField, fields.DurationField),
                # DurationField.
                (fields.DurationField, fields.DurationField, fields.DurationField),
                # TimeField.
                (fields.TimeField, fields.DurationField, fields.TimeField),
                (fields.TimeField, fields.TimeField, fields.DurationField),
            ],
        },
    ]

    _connector_combinators = defaultdict(list)

    def register_combinable_fields(lhs, connector, rhs, result):
        """
        Register combinable types:
            lhs <connector> rhs -> result
        e.g.
            register_combinable_fields(
                IntegerField, Combinable.ADD, FloatField, FloatField
            )
        """
        _connector_combinators[connector].append((lhs, rhs, result))

    for d in _connector_combinations:
        for connector, field_types in d.items():
            for lhs, rhs, result in field_types:
                register_combinable_fields(lhs, connector, rhs, result)

    @functools.lru_cache(maxsize=128)
    def _resolve_combined_type(connector, lhs_type, rhs_type):
        combinators = _connector_combinators.get(connector, ())
        for combinator_lhs_type, combinator_rhs_type, combined_type in combinators:
            if issubclass(lhs_type, combinator_lhs_type) and issubclass(
                rhs_type, combinator_rhs_type
            ):
                return combined_type

    class CombinedExpression(SQLiteNumericMixin, Expression):
        def __init__(self, lhs, connector, rhs, output_field=None):
            super().__init__(output_field=output_field)
            self.connector = connector
            self.lhs = lhs
            self.rhs = rhs

        def __repr__(self):
            return "<{}: {}>".format(self.__class__.__name__, self)

        def __str__(self):
            return "{} {} {}".format(self.lhs, self.connector, self.rhs)

        def get_source_expressions(self):
            return [self.lhs, self.rhs]

        def set_source_expressions(self, exprs):
            self.lhs, self.rhs = exprs

        def _resolve_output_field(self):
            # We avoid using super() here for reasons given in
            # Expression._resolve_output_field()
            combined_type = _resolve_combined_type(
                self.connector,
                type(self.lhs._output_field_or_none),
                type(self.rhs._output_field_or_none),
            )
            if combined_type is None:
                raise FieldError(
                    f"Cannot infer type of {self.connector!r} expression involving these "
                    f"types: {self.lhs.output_field.__class__.__name__}, "
                    f"{self.rhs.output_field.__class__.__name__}. You must set "
                    f"output_field."
                )
            return combined_type()

        def as_sql(self, compiler, connection):
            expressions = []
            expression_params = []
            sql, params = compiler.compile(self.lhs)
            expressions.append(sql)
            expression_params.extend(params)
            sql, params = compiler.compile(self.rhs)
            expressions.append(sql)
            expression_params.extend(params)
            # order of precedence
            expression_wrapper = "(%s)"
            sql = connection.ops.combine_expression(self.connector, expressions)
            return expression_wrapper % sql, expression_params

        def resolve_expression(
            self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False
        ):
            resolved = super().resolve_expression(
                query,
                allow_joins,
                reuse,
                summarize,
                for_save,
            )
            if not isinstance(self, (DurationExpression, TemporalSubtraction)):
                try:
                    lhs_type = resolved.lhs.output_field.get_internal_type()
                except (AttributeError, FieldError):
                    lhs_type = None
                try:
                    rhs_type = resolved.rhs.output_field.get_internal_type()
                except (AttributeError, FieldError):
                    rhs_type = None
                if "DurationField" in {lhs_type, rhs_type} and lhs_type != rhs_type:
                    return DurationExpression(
                        resolved.lhs, resolved.connector, resolved.rhs
                    )
                datetime_fields = {"DateField", "DateTimeField", "TimeField"}
                if (
                    self.connector == self.SUB
                    and lhs_type in datetime_fields
                    and lhs_type == rhs_type
                ):
                    return TemporalSubtraction(resolved.lhs, resolved.rhs)
            return resolved

        @cached_property
        def allowed_default(self):
            return self.lhs.allowed_default and self.rhs.allowed_default

    class DurationExpression(CombinedExpression):
        def compile(self, side, compiler, connection):
            try:
                output = side.output_field
            except FieldError:
                pass
            else:
                if output.get_internal_type() == "DurationField":
                    sql, params = compiler.compile(side)
                    return connection.ops.format_for_duration_arithmetic(sql), params
            return compiler.compile(side)

        def as_sql(self, compiler, connection):
            if connection.features.has_native_duration_field:
                return super().as_sql(compiler, connection)
            connection.ops.check_expression_support(self)
            expressions = []
            expression_params = []
            sql, params = self.compile(self.lhs, compiler, connection)
            expressions.append(sql)
            expression_params.extend(params)
            sql, params = self.compile(self.rhs, compiler, connection)
            expressions.append(sql)
            expression_params.extend(params)
            # order of precedence
            expression_wrapper = "(%s)"
            sql = connection.ops.combine_duration_expression(self.connector, expressions)
            return expression_wrapper % sql, expression_params

        def as_sqlite(self, compiler, connection, **extra_context):
            sql, params = self.as_sql(compiler, connection, **extra_context)
            if self.connector in {Combinable.MUL, Combinable.DIV}:
                try:
                    lhs_type = self.lhs.output_field.get_internal_type()
                    rhs_type = self.rhs.output_field.get_internal_type()
                except (AttributeError, FieldError):
                    pass
                else:
                    allowed_fields = {
                        "DecimalField",
                        "DurationField",
                        "FloatField",
                        "IntegerField",
                    }
                    if lhs_type not in allowed_fields or rhs_type not in allowed_fields:
                        raise DatabaseError(
                            f"Invalid arguments for operator {self.connector}."
                        )
            return sql, params

    class TemporalSubtraction(CombinedExpression):
        output_field = fields.DurationField()

        def __init__(self, lhs, rhs):
            super().__init__(lhs, self.SUB, rhs)

        def as_sql(self, compiler, connection):
            connection.ops.check_expression_support(self)
            lhs = compiler.compile(self.lhs)
            rhs = compiler.compile(self.rhs)
            return connection.ops.subtract_temporals(
                self.lhs.output_field.get_internal_type(), lhs, rhs
            )

    @deconstructible(path="django.db.models.F")
    class F(Combinable):
        """An object capable of resolving references to existing query objects."""

        allowed_default = False

        def __init__(self, name):
            """
            Arguments:
             * name: the name of the field this expression references
            """
            self.name = name

        def __repr__(self):
            return "{}({})".format(self.__class__.__name__, self.name)

        def __getitem__(self, subscript):
            return Sliced(self, subscript)

        def __contains__(self, other):
            # Disable old-style iteration protocol inherited from implementing
            # __getitem__() to prevent this method from hanging.
            raise TypeError(f"argument of type '{self.__class__.__name__}' is not iterable")

        def resolve_expression(
            self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False
        ):
            return query.resolve_ref(self.name, allow_joins, reuse, summarize)

        def replace_expressions(self, replacements):
            return replacements.get(self, self)

        def asc(self, **kwargs):
            return OrderBy(self, **kwargs)

        def desc(self, **kwargs):
            return OrderBy(self, descending=True, **kwargs)

        def __eq__(self, other):
            return self.__class__ == other.__class__ and self.name == other.name

        def __hash__(self):
            return hash(self.name)

        def copy(self):
            return copy.copy(self)

    class ResolvedOuterRef(F):
        """
        An object that contains a reference to an outer query.

        In this case, the reference to the outer query has been resolved because
        the inner query has been used as a subquery.
        """

        contains_aggregate = False
        contains_over_clause = False

        def as_sql(self, *args, **kwargs):
            raise ValueError(
                "This queryset contains a reference to an outer query and may "
                "only be used in a subquery."
            )

        def resolve_expression(self, *args, **kwargs):
            col = super().resolve_expression(*args, **kwargs)
            if col.contains_over_clause:
                raise NotSupportedError(
                    f"Referencing outer query window expression is not supported: "
                    f"{self.name}."
                )
            # FIXME: Rename possibly_multivalued to multivalued and fix detection
            # for non-multivalued JOINs (e.g. foreign key fields). This should take
            # into account only many-to-many and one-to-many relationships.
            col.possibly_multivalued = LOOKUP_SEP in self.name
            return col

        def relabeled_clone(self, relabels):
            return self

        def get_group_by_cols(self):
            return []

    class OuterRef(F):
        contains_aggregate = False
        contains_over_clause = False

        def resolve_expression(self, *args, **kwargs):
            if isinstance(self.name, self.__class__):
                return self.name
            return ResolvedOuterRef(self.name)

        def relabeled_clone(self, relabels):
            return self

    class Sliced(F):
        """
        An object that contains a slice of an F expression.

        Object resolves the column on which the slicing is applied, and then
        applies the slicing if possible.
        """

        def __init__(self, obj, subscript):
            super().__init__(obj.name)
            self.obj = obj
            if isinstance(subscript, int):
                if subscript < 0:
                    raise ValueError("Negative indexing is not supported.")
                self.start = subscript + 1
                self.length = 1
            elif isinstance(subscript, slice):
                if (subscript.start is not None and subscript.start < 0) or (
                    subscript.stop is not None and subscript.stop < 0
                ):
                    raise ValueError("Negative indexing is not supported.")
                if subscript.step is not None:
                    raise ValueError("Step argument is not supported.")
                if subscript.stop and subscript.start and subscript.stop < subscript.start:
                    raise ValueError("Slice stop must be greater than slice start.")
                self.start = 1 if subscript.start is None else subscript.start + 1
                if subscript.stop is None:
                    self.length = None
                else:
                    self.length = subscript.stop - (subscript.start or 0)
            else:
                raise TypeError("Argument to slice must be either int or slice instance.")

        def __repr__(self):
            start = self.start - 1
            stop = None if self.length is None else start + self.length
            subscript = slice(start, stop)
            return f"{self.__class__.__qualname__}({self.obj!r}, {subscript!r})"

        def resolve_expression(
            self,
            query=None,
            allow_joins=True,
            reuse=None,
            summarize=False,
            for_save=False,
        ):
            resolved = query.resolve_ref(self.name, allow_joins, reuse, summarize)
            if isinstance(self.obj, (OuterRef, self.__class__)):
                expr = self.obj.resolve_expression(
                    query, allow_joins, reuse, summarize, for_save
                )
            else:
                expr = resolved
            return resolved.output_field.slice_expression(expr, self.start, self.length)

    @deconstructible(path="django.db.models.Func")
    class Func(SQLiteNumericMixin, Expression):
        """An SQL function call."""

        function = None
        template = "%(function)s(%(expressions)s)"
        arg_joiner = ", "
        arity = None  # The number of arguments the function accepts.

        def __init__(self, *expressions, output_field=None, **extra):
            if self.arity is not None and len(expressions) != self.arity:
                raise TypeError(
                    "'%s' takes exactly %s %s (%s given)"
                    % (
                        self.__class__.__name__,
                        self.arity,
                        "argument" if self.arity == 1 else "arguments",
                        len(expressions),
                    )
                )
            super().__init__(output_field=output_field)
            self.source_expressions = self._parse_expressions(*expressions)
            self.extra = extra

        def __repr__(self):
            args = self.arg_joiner.join(str(arg) for arg in self.source_expressions)
            extra = {**self.extra, **self._get_repr_options()}
            if extra:
                extra = ", ".join(
                    str(key) + "=" + str(val) for key, val in sorted(extra.items())
                )
                return "{}({}, {})".format(self.__class__.__name__, args, extra)
            return "{}({})".format(self.__class__.__name__, args)

        def _get_repr_options(self):
            """Return a dict of extra __init__() options to include in the repr."""
            return {}

        def get_source_expressions(self):
            return self.source_expressions

        def set_source_expressions(self, exprs):
            self.source_expressions = exprs

        def as_sql(
            self,
            compiler,
            connection,
            function=None,
            template=None,
            arg_joiner=None,
            **extra_context,
        ):
            connection.ops.check_expression_support(self)
            sql_parts = []
            params = []
            for arg in self.source_expressions:
                try:
                    arg_sql, arg_params = compiler.compile(arg)
                except EmptyResultSet:
                    empty_result_set_value = getattr(
                        arg, "empty_result_set_value", NotImplemented
                    )
                    if empty_result_set_value is NotImplemented:
                        raise
                    arg_sql, arg_params = compiler.compile(Value(empty_result_set_value))
                except FullResultSet:
                    arg_sql, arg_params = compiler.compile(Value(True))
                sql_parts.append(arg_sql)
                params.extend(arg_params)
            data = {**self.extra, **extra_context}
            # Use the first supplied value in this order: the parameter to this
            # method, a value supplied in __init__()'s **extra (the value in
            # `data`), or the value defined on the class.
            if function is not None:
                data["function"] = function
            else:
                data.setdefault("function", self.function)
            template = template or data.get("template", self.template)
            arg_joiner = arg_joiner or data.get("arg_joiner", self.arg_joiner)
            data["expressions"] = data["field"] = arg_joiner.join(sql_parts)
            return template % data, params

        def copy(self):
            copy = super().copy()
            copy.source_expressions = self.source_expressions[:]
            copy.extra = self.extra.copy()
            return copy

        @cached_property
        def allowed_default(self):
            return all(expression.allowed_default for expression in self.source_expressions)

    @deconstructible(path="django.db.models.Value")
    class Value(SQLiteNumericMixin, Expression):
        """Represent a wrapped value as a node within an expression."""

        # Provide a default value for `for_save` in order to allow unresolved
        # instances to be compiled until a decision is taken in #25425.
        for_save = False
        allowed_default = True

        def __init__(self, value, output_field=None):
            """
            Arguments:
             * value: the value this expression represents. The value will be
               added into the sql parameter list and properly quoted.

             * output_field: an instance of the model field type that this
               expression will return, such as IntegerField() or CharField().
            """
            super().__init__(output_field=output_field)
            self.value = value

        def __repr__(self):
            return f"{self.__class__.__name__}({self.value!r})"

        def as_sql(self, compiler, connection):
            connection.ops.check_expression_support(self)
            val = self.value
            output_field = self._output_field_or_none
            if output_field is not None:
                if self.for_save:
                    val = output_field.get_db_prep_save(val, connection=connection)
                else:
                    val = output_field.get_db_prep_value(val, connection=connection)
                if hasattr(output_field, "get_placeholder"):
                    return output_field.get_placeholder(val, compiler, connection), [val]
            if val is None:
                # oracledb does not always convert None to the appropriate
                # NULL type (like in case expressions using numbers), so we
                # use a literal SQL NULL
                return "NULL", []
            return "%s", [val]

        def resolve_expression(
            self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False
        ):
            c = super().resolve_expression(query, allow_joins, reuse, summarize, for_save)
            c.for_save = for_save
            return c

        def get_group_by_cols(self):
            return []

        def _resolve_output_field(self):
            if isinstance(self.value, str):
                return fields.CharField()
            if isinstance(self.value, bool):
                return fields.BooleanField()
            if isinstance(self.value, int):
                return fields.IntegerField()
            if isinstance(self.value, float):
                return fields.FloatField()
            if isinstance(self.value, datetime.datetime):
                return fields.DateTimeField()
            if isinstance(self.value, datetime.date):
                return fields.DateField()
            if isinstance(self.value, datetime.time):
                return fields.TimeField()
            if isinstance(self.value, datetime.timedelta):
                return fields.DurationField()
            if isinstance(self.value, Decimal):
                return fields.DecimalField()
            if isinstance(self.value, bytes):
                return fields.BinaryField()
            if isinstance(self.value, UUID):
                return fields.UUIDField()

        @property
        def empty_result_set_value(self):
            return self.value

    class RawSQL(Expression):
        allowed_default = True

        def __init__(self, sql, params, output_field=None):
            if output_field is None:
                output_field = fields.Field()
            self.sql, self.params = sql, params
            super().__init__(output_field=output_field)

        def __repr__(self):
            return "{}({}, {})".format(self.__class__.__name__, self.sql, self.params)

        def as_sql(self, compiler, connection):
            return "(%s)" % self.sql, self.params

        def get_group_by_cols(self):
            return [self]

        def resolve_expression(
            self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False
        ):
            # Resolve parents fields used in raw SQL.
            if query.model:
                for parent in query.model._meta.all_parents:
                    for parent_field in parent._meta.local_fields:
                        if parent_field.column.lower() in self.sql.lower():
                            query.resolve_ref(
                                parent_field.name, allow_joins, reuse, summarize
                            )
                            break
            return super().resolve_expression(
                query, allow_joins, reuse, summarize, for_save
            )

    class Star(Expression):
        def __repr__(self):
            return "'*'"

        def as_sql(self, compiler, connection):
            return "*", []

    class DatabaseDefault(Expression):
        """
        Expression to use DEFAULT keyword during insert otherwise the underlying expression.
        """

        def __init__(self, expression, output_field=None):
            super().__init__(output_field)
            self.expression = expression

        def get_source_expressions(self):
            return [self.expression]

        def set_source_expressions(self, exprs):
            (self.expression,) = exprs

        def resolve_expression(
            self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False
        ):
            resolved_expression = self.expression.resolve_expression(
                query=query,
                allow_joins=allow_joins,
                reuse=reuse,
                summarize=summarize,
                for_save=for_save,
            )
            # Defaults used outside an INSERT context should resolve to their
            # underlying expression.
            if not for_save:
                return resolved_expression
            return DatabaseDefault(
                resolved_expression, output_field=self._output_field_or_none
            )

        def as_sql(self, compiler, connection):
            if not connection.features.supports_default_keyword_in_insert:
                return compiler.compile(self.expression)
            return "DEFAULT", []

    class Col(Expression):
        contains_column_references = True
        possibly_multivalued = False

        def __init__(self, alias, target, output_field=None):
            if output_field is None:
                output_field = target
            super().__init__(output_field=output_field)
            self.alias, self.target = alias, target

        def __repr__(self):
            alias, target = self.alias, self.target
            identifiers = (alias, str(target)) if alias else (str(target),)
            return "{}({})".format(self.__class__.__name__, ", ".join(identifiers))

        def as_sql(self, compiler, connection):
            alias, column = self.alias, self.target.column
            identifiers = (alias, column) if alias else (column,)
            sql = ".".join(map(compiler.quote_name_unless_alias, identifiers))
            return sql, []

        def relabeled_clone(self, relabels):
            if self.alias is None:
                return self
            return self.__class__(
                relabels.get(self.alias, self.alias), self.target, self.output_field
            )

        def get_group_by_cols(self):
            return [self]

        def get_db_converters(self, connection):
            if self.target == self.output_field:
                return self.output_field.get_db_converters(connection)
            return self.output_field.get_db_converters(
                connection
            ) + self.target.get_db_converters(connection)

    class ColPairs(Expression):
        def __init__(self, alias, targets, sources, output_field):
            super().__init__(output_field=output_field)
            self.alias = alias
            self.targets = targets
            self.sources = sources

        def __len__(self):
            return len(self.targets)

        def __iter__(self):
            return iter(self.get_cols())

        def __repr__(self):
            return (
                f"{self.__class__.__name__}({self.alias!r}, {self.targets!r}, "
                f"{self.sources!r}, {self.output_field!r})"
            )

        def get_cols(self):
            return [
                Col(self.alias, target, source)
                for target, source in zip(self.targets, self.sources)
            ]

        def get_source_expressions(self):
            return self.get_cols()

        def set_source_expressions(self, exprs):
            assert all(isinstance(expr, Col) and expr.alias == self.alias for expr in exprs)
            self.targets = [col.target for col in exprs]
            self.sources = [col.field for col in exprs]

        def as_sql(self, compiler, connection):
            cols_sql = []
            cols_params = []
            cols = self.get_cols()

            for col in cols:
                sql, params = col.as_sql(compiler, connection)
                cols_sql.append(sql)
                cols_params.extend(params)

            return ", ".join(cols_sql), cols_params

        def relabeled_clone(self, relabels):
            return self.__class__(
                relabels.get(self.alias, self.alias), self.targets, self.sources, self.field
            )

        def resolve_expression(self, *args, **kwargs):
            return self

        def select_format(self, compiler, sql, params):
            return sql, params

    class Ref(Expression):
        """
        Reference to column alias of the query. For example, Ref('sum_cost') in
        qs.annotate(sum_cost=Sum('cost')) query.
        """

        def __init__(self, refs, source):
            super().__init__()
            self.refs, self.source = refs, source

        def __repr__(self):
            return "{}({}, {})".format(self.__class__.__name__, self.refs, self.source)

        def get_source_expressions(self):
            return [self.source]

        def set_source_expressions(self, exprs):
            (self.source,) = exprs

        def resolve_expression(
            self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False
        ):
            # The sub-expression `source` has already been resolved, as this is
            # just a reference to the name of `source`.
            return self

        def get_refs(self):
            return {self.refs}

        def relabeled_clone(self, relabels):
            clone = self.copy()
            clone.source = self.source.relabeled_clone(relabels)
            return clone

        def as_sql(self, compiler, connection):
            return connection.ops.quote_name(self.refs), []

        def get_group_by_cols(self):
            return [self]

    class ExpressionList(Func):
        """
        An expression containing multiple expressions. Can be used to provide a
        list of expressions as an argument to another expression, like a partition
        clause.
        """

        template = "%(expressions)s"

        def __str__(self):
            return self.arg_joiner.join(str(arg) for arg in self.source_expressions)

        def as_sql(self, *args, **kwargs):
            if not self.source_expressions:
                return "", ()
            return super().as_sql(*args, **kwargs)

        def as_sqlite(self, compiler, connection, **extra_context):
            # Casting to numeric is unnecessary.
            return self.as_sql(compiler, connection, **extra_context)

        def get_group_by_cols(self):
            group_by_cols = []
            for expr in self.get_source_expressions():
                group_by_cols.extend(expr.get_group_by_cols())
            return group_by_cols

    class OrderByList(ExpressionList):
        allowed_default = False
        template = "ORDER BY %(expressions)s"

        def __init__(self, *expressions, **extra):
            expressions = (
                (
                    OrderBy(F(expr[1:]), descending=True)
                    if isinstance(expr, str) and expr[0] == "-"
                    else expr
                )
                for expr in expressions
            )
            super().__init__(*expressions, **extra)

    @deconstructible(path="django.db.models.ExpressionWrapper")
    class ExpressionWrapper(SQLiteNumericMixin, Expression):
        """
        An expression that can wrap another expression so that it can provide
        extra context to the inner expression, such as the output_field.
        """

        def __init__(self, expression, output_field):
            super().__init__(output_field=output_field)
            self.expression = expression

        def set_source_expressions(self, exprs):
            self.expression = exprs[0]

        def get_source_expressions(self):
            return [self.expression]

        def get_group_by_cols(self):
            if isinstance(self.expression, Expression):
                expression = self.expression.copy()
                expression.output_field = self.output_field
                return expression.get_group_by_cols()
            # For non-expressions e.g. an SQL WHERE clause, the entire
            # `expression` must be included in the GROUP BY clause.
            return super().get_group_by_cols()

        def as_sql(self, compiler, connection):
            return compiler.compile(self.expression)

        def __repr__(self):
            return "{}({})".format(self.__class__.__name__, self.expression)

        @property
        def allowed_default(self):
            return self.expression.allowed_default

    class NegatedExpression(ExpressionWrapper):
        """The logical negation of a conditional expression."""

        def __init__(self, expression):
            super().__init__(expression, output_field=fields.BooleanField())

        def __invert__(self):
            return self.expression.copy()

        def as_sql(self, compiler, connection):
            try:
                sql, params = super().as_sql(compiler, connection)
            except EmptyResultSet:
                features = compiler.connection.features
                if not features.supports_boolean_expr_in_select_clause:
                    return "1=1", ()
                return compiler.compile(Value(True))
            ops = compiler.connection.ops
            # Some database backends (e.g. Oracle) don't allow EXISTS() and filters
            # to be compared to another expression unless they're wrapped in a CASE
            # WHEN.
            if not ops.conditional_expression_supported_in_where_clause(self.expression):
                return f"CASE WHEN {sql} = 0 THEN 1 ELSE 0 END", params
            return f"NOT {sql}", params

        def resolve_expression(
            self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False
        ):
            resolved = super().resolve_expression(
                query, allow_joins, reuse, summarize, for_save
            )
            if not getattr(resolved.expression, "conditional", False):
                raise TypeError("Cannot negate non-conditional expressions.")
            return resolved

        def select_format(self, compiler, sql, params):
            # Wrap boolean expressions with a CASE WHEN expression if a database
            # backend (e.g. Oracle) doesn't support boolean expression in SELECT or
            # GROUP BY list.
            expression_supported_in_where_clause = (
                compiler.connection.ops.conditional_expression_supported_in_where_clause
            )
            if (
                not compiler.connection.features.supports_boolean_expr_in_select_clause
                # Avoid double wrapping.
                and expression_supported_in_where_clause(self.expression)
            ):
                sql = "CASE WHEN {} THEN 1 ELSE 0 END".format(sql)
            return sql, params

    @deconstructible(path="django.db.models.When")
    class When(Expression):
        template = "WHEN %(condition)s THEN %(result)s"
        # This isn't a complete conditional expression, must be used in Case().
        conditional = False

        def __init__(self, condition=None, then=None, **lookups):
            if lookups:
                if condition is None:
                    condition, lookups = Q(**lookups), None
                elif getattr(condition, "conditional", False):
                    condition, lookups = Q(condition, **lookups), None
            if condition is None or not getattr(condition, "conditional", False) or lookups:
                raise TypeError(
                    "When() supports a Q object, a boolean expression, or lookups "
                    "as a condition."
                )
            if isinstance(condition, Q) and not condition:
                raise ValueError("An empty Q() can't be used as a When() condition.")
            super().__init__(output_field=None)
            self.condition = condition
            self.result = self._parse_expressions(then)[0]

        def __str__(self):
            return "WHEN %r THEN %r" % (self.condition, self.result)

        def __repr__(self):
            return "<%s: %s>" % (self.__class__.__name__, self)

        def get_source_expressions(self):
            return [self.condition, self.result]

        def set_source_expressions(self, exprs):
            self.condition, self.result = exprs

        def get_source_fields(self):
            # We're only interested in the fields of the result expressions.
            return [self.result._output_field_or_none]

        def as_sql(self, compiler, connection, template=None, **extra_context):
            connection.ops.check_expression_support(self)
            template_params = extra_context
            sql_params = []
            condition_sql, condition_params = compiler.compile(self.condition)
            template_params["condition"] = condition_sql
            result_sql, result_params = compiler.compile(self.result)
            template_params["result"] = result_sql
            template = template or self.template
            return template % template_params, (
                *sql_params,
                *condition_params,
                *result_params,
            )

        def get_group_by_cols(self):
            # This is not a complete expression and cannot be used in GROUP BY.
            cols = []
            for source in self.get_source_expressions():
                cols.extend(source.get_group_by_cols())
            return cols

        @cached_property
        def allowed_default(self):
            return self.condition.allowed_default and self.result.allowed_default

    @deconstructible(path="django.db.models.Case")
    class Case(SQLiteNumericMixin, Expression):
        """
        An SQL searched CASE expression:

            CASE
                WHEN n > 0
                    THEN 'positive'
                WHEN n < 0
                    THEN 'negative'
                ELSE 'zero'
            END
        """

        template = "CASE %(cases)s ELSE %(default)s END"
        case_joiner = " "

        def __init__(self, *cases, default=None, output_field=None, **extra):
            if not all(isinstance(case, When) for case in cases):
                raise TypeError("Positional arguments must all be When objects.")
            super().__init__(output_field)
            self.cases = list(cases)
            self.default = self._parse_expressions(default)[0]
            self.extra = extra

        def __str__(self):
            return "CASE %s, ELSE %r" % (
                ", ".join(str(c) for c in self.cases),
                self.default,
            )

        def __repr__(self):
            return "<%s: %s>" % (self.__class__.__name__, self)

        def get_source_expressions(self):
            return self.cases + [self.default]

        def set_source_expressions(self, exprs):
            *self.cases, self.default = exprs

        def copy(self):
            c = super().copy()
            c.cases = c.cases[:]
            return c

        def as_sql(
            self, compiler, connection, template=None, case_joiner=None, **extra_context
        ):
            connection.ops.check_expression_support(self)
            if not self.cases:
                return compiler.compile(self.default)
            template_params = {**self.extra, **extra_context}
            case_parts = []
            sql_params = []
            for case in self.cases:
                try:
                    case_sql, case_params = compiler.compile(case)
                except EmptyResultSet:
                    continue
                except FullResultSet:
                    default_sql, default_params = compiler.compile(case.result)
                    break
                case_parts.append(case_sql)
                sql_params.extend(case_params)
            else:
                default_sql, default_params = compiler.compile(self.default)
            if not case_parts:
                return default_sql, default_params
            case_joiner = case_joiner or self.case_joiner
            template_params["cases"] = case_joiner.join(case_parts)
            template_params["default"] = default_sql
            sql_params.extend(default_params)
            template = template or template_params.get("template", self.template)
            sql = template % template_params
            if self._output_field_or_none is not None:
                sql = connection.ops.unification_cast_sql(self.output_field) % sql
            return sql, sql_params

        def get_group_by_cols(self):
            if not self.cases:
                return self.default.get_group_by_cols()
            return super().get_group_by_cols()

        @cached_property
        def allowed_default(self):
            return self.default.allowed_default and all(
                case_.allowed_default for case_ in self.cases
            )

    class Subquery(BaseExpression, Combinable):
        """
        An explicit subquery. It may contain OuterRef() references to the outer
        query which will be resolved when it is applied to that query.
        """

        template = "(%(subquery)s)"
        contains_aggregate = False
        empty_result_set_value = None
        subquery = True

        def __init__(self, queryset, output_field=None, **extra):
            # Allow the usage of both QuerySet and sql.Query objects.
            self.query = getattr(queryset, "query", queryset).clone()
            self.query.subquery = True
            self.extra = extra
            super().__init__(output_field)

        def get_source_expressions(self):
            return [self.query]

        def set_source_expressions(self, exprs):
            self.query = exprs[0]

        def _resolve_output_field(self):
            return self.query.output_field

        def copy(self):
            clone = super().copy()
            clone.query = clone.query.clone()
            return clone

        @property
        def external_aliases(self):
            return self.query.external_aliases

        def get_external_cols(self):
            return self.query.get_external_cols()

        def as_sql(self, compiler, connection, template=None, **extra_context):
            connection.ops.check_expression_support(self)
            template_params = {**self.extra, **extra_context}
            subquery_sql, sql_params = self.query.as_sql(compiler, connection)
            template_params["subquery"] = subquery_sql[1:-1]

            template = template or template_params.get("template", self.template)
            sql = template % template_params
            return sql, sql_params

        def get_group_by_cols(self):
            return self.query.get_group_by_cols(wrapper=self)

    class Exists(Subquery):
        template = "EXISTS(%(subquery)s)"
        output_field = fields.BooleanField()
        empty_result_set_value = False

        def __init__(self, queryset, **kwargs):
            super().__init__(queryset, **kwargs)
            self.query = self.query.exists()

        def select_format(self, compiler, sql, params):
            # Wrap EXISTS() with a CASE WHEN expression if a database backend
            # (e.g. Oracle) doesn't support boolean expression in SELECT or GROUP
            # BY list.
            if not compiler.connection.features.supports_boolean_expr_in_select_clause:
                sql = "CASE WHEN {} THEN 1 ELSE 0 END".format(sql)
            return sql, params

        def as_sql(self, compiler, *args, **kwargs):
            try:
                return super().as_sql(compiler, *args, **kwargs)
            except EmptyResultSet:
                features = compiler.connection.features
                if not features.supports_boolean_expr_in_select_clause:
                    return "1=0", ()
                return compiler.compile(Value(False))

    @deconstructible(path="django.db.models.OrderBy")
    class OrderBy(Expression):
        template = "%(expression)s %(ordering)s"
        conditional = False
        constraint_validation_compatible = False
        allows_composite_expressions = True

        def __init__(self, expression, descending=False, nulls_first=None, nulls_last=None):
            if nulls_first and nulls_last:
                raise ValueError("nulls_first and nulls_last are mutually exclusive")
            if nulls_first is False or nulls_last is False:
                raise ValueError("nulls_first and nulls_last values must be True or None.")
            self.nulls_first = nulls_first
            self.nulls_last = nulls_last
            self.descending = descending
            if not hasattr(expression, "resolve_expression"):
                raise ValueError("expression must be an expression type")
            self.expression = expression

        def __repr__(self):
            return "{}({}, descending={})".format(
                self.__class__.__name__, self.expression, self.descending
            )

        def set_source_expressions(self, exprs):
            self.expression = exprs[0]

        def get_source_expressions(self):
            return [self.expression]

        def as_sql(self, compiler, connection, template=None, **extra_context):
            if isinstance(self.expression, ColPairs):
                sql_parts = []
                params = []
                for col in self.expression.get_cols():
                    copy = self.copy()
                    copy.set_source_expressions([col])
                    sql, col_params = compiler.compile(copy)
                    sql_parts.append(sql)
                    params.extend(col_params)
                return ", ".join(sql_parts), params
            template = template or self.template
            if connection.features.supports_order_by_nulls_modifier:
                if self.nulls_last:
                    template = "%s NULLS LAST" % template
                elif self.nulls_first:
                    template = "%s NULLS FIRST" % template
            else:
                if self.nulls_last and not (
                    self.descending and connection.features.order_by_nulls_first
                ):
                    template = "%%(expression)s IS NULL, %s" % template
                elif self.nulls_first and not (
                    not self.descending and connection.features.order_by_nulls_first
                ):
                    template = "%%(expression)s IS NOT NULL, %s" % template
            connection.ops.check_expression_support(self)
            expression_sql, params = compiler.compile(self.expression)
            placeholders = {
                "expression": expression_sql,
                "ordering": "DESC" if self.descending else "ASC",
                **extra_context,
            }
            params *= template.count("%(expression)s")
            return (template % placeholders).rstrip(), params

        def as_oracle(self, compiler, connection):
            # Oracle < 23c doesn't allow ORDER BY EXISTS() or filters unless it's
            # wrapped in a CASE WHEN.
            if (
                not connection.features.supports_boolean_expr_in_select_clause
                and connection.ops.conditional_expression_supported_in_where_clause(
                    self.expression
                )
            ):
                copy = self.copy()
                copy.expression = Case(
                    When(self.expression, then=True),
                    default=False,
                )
                return copy.as_sql(compiler, connection)
            return self.as_sql(compiler, connection)

        def get_group_by_cols(self):
            cols = []
            for source in self.get_source_expressions():
                cols.extend(source.get_group_by_cols())
            return cols

        def reverse_ordering(self):
            self.descending = not self.descending
            if self.nulls_first:
                self.nulls_last = True
                self.nulls_first = None
            elif self.nulls_last:
                self.nulls_first = True
                self.nulls_last = None
            return self

        def asc(self):
            self.descending = False

        def desc(self):
            self.descending = True

    class Window(SQLiteNumericMixin, Expression):
        template = "%(expression)s OVER (%(window)s)"
        # Although the main expression may either be an aggregate or an
        # expression with an aggregate function, the GROUP BY that will
        # be introduced in the query as a result is not desired.
        contains_aggregate = False
        contains_over_clause = True

        def __init__(
            self,
            expression,
            partition_by=None,
            order_by=None,
            frame=None,
            output_field=None,
        ):
            self.partition_by = partition_by
            self.order_by = order_by
            self.frame = frame

            if not getattr(expression, "window_compatible", False):
                raise ValueError(
                    "Expression '%s' isn't compatible with OVER clauses."
                    % expression.__class__.__name__
                )

            if self.partition_by is not None:
                if not isinstance(self.partition_by, (tuple, list)):
                    self.partition_by = (self.partition_by,)
                self.partition_by = ExpressionList(*self.partition_by)

            if self.order_by is not None:
                if isinstance(self.order_by, (list, tuple)):
                    self.order_by = OrderByList(*self.order_by)
                elif isinstance(self.order_by, (BaseExpression, str)):
                    self.order_by = OrderByList(self.order_by)
                else:
                    raise ValueError(
                        "Window.order_by must be either a string reference to a "
                        "field, an expression, or a list or tuple of them."
                    )
            super().__init__(output_field=output_field)
            self.source_expression = self._parse_expressions(expression)[0]

        def _resolve_output_field(self):
            return self.source_expression.output_field

        def get_source_expressions(self):
            return [self.source_expression, self.partition_by, self.order_by, self.frame]

        def set_source_expressions(self, exprs):
            self.source_expression, self.partition_by, self.order_by, self.frame = exprs

        def as_sql(self, compiler, connection, template=None):
            connection.ops.check_expression_support(self)
            if not connection.features.supports_over_clause:
                raise NotSupportedError("This backend does not support window expressions.")
            expr_sql, params = compiler.compile(self.source_expression)
            window_sql, window_params = [], ()

            if self.partition_by is not None:
                sql_expr, sql_params = self.partition_by.as_sql(
                    compiler=compiler,
                    connection=connection,
                    template="PARTITION BY %(expressions)s",
                )
                window_sql.append(sql_expr)
                window_params += tuple(sql_params)

            if self.order_by is not None:
                order_sql, order_params = compiler.compile(self.order_by)
                window_sql.append(order_sql)
                window_params += tuple(order_params)

            if self.frame:
                frame_sql, frame_params = compiler.compile(self.frame)
                window_sql.append(frame_sql)
                window_params += tuple(frame_params)

            template = template or self.template

            return (
                template % {"expression": expr_sql, "window": " ".join(window_sql).strip()},
                (*params, *window_params),
            )

        def as_sqlite(self, compiler, connection):
            if isinstance(self.output_field, fields.DecimalField):
                # Casting to numeric must be outside of the window expression.
                copy = self.copy()
                source_expressions = copy.get_source_expressions()
                source_expressions[0].output_field = fields.FloatField()
                copy.set_source_expressions(source_expressions)
                return super(Window, copy).as_sqlite(compiler, connection)
            return self.as_sql(compiler, connection)

        def __str__(self):
            return "{} OVER ({}{}{})".format(
                str(self.source_expression),
                "PARTITION BY " + str(self.partition_by) if self.partition_by else "",
                str(self.order_by or ""),
                str(self.frame or ""),
            )

        def __repr__(self):
            return "<%s: %s>" % (self.__class__.__name__, self)

        def get_group_by_cols(self):
            group_by_cols = []
            if self.partition_by:
                group_by_cols.extend(self.partition_by.get_group_by_cols())
            if self.order_by is not None:
                group_by_cols.extend(self.order_by.get_group_by_cols())
            return group_by_cols

    class WindowFrameExclusion(Enum):
        CURRENT_ROW = "CURRENT ROW"
        GROUP = "GROUP"
        TIES = "TIES"
        NO_OTHERS = "NO OTHERS"

        def __repr__(self):
            return f"{self.__class__.__qualname__}.{self._name_}"

    class WindowFrame(Expression):
        """
        Model the frame clause in window expressions. There are two types of frame
        clauses which are subclasses, however, all processing and validation (by no
        means intended to be complete) is done here. Thus, providing an end for a
        frame is optional (the default is UNBOUNDED FOLLOWING, which is the last
        row in the frame).
        """

        template = "%(frame_type)s BETWEEN %(start)s AND %(end)s%(exclude)s"

        def __init__(self, start=None, end=None, exclusion=None):
            self.start = Value(start)
            self.end = Value(end)
            if not isinstance(exclusion, (NoneType, WindowFrameExclusion)):
                raise TypeError(
                    f"{self.__class__.__qualname__}.exclusion must be a "
                    "WindowFrameExclusion instance."
                )
            self.exclusion = exclusion

        def set_source_expressions(self, exprs):
            self.start, self.end = exprs

        def get_source_expressions(self):
            return [self.start, self.end]

        def get_exclusion(self):
            if self.exclusion is None:
                return ""
            return f" EXCLUDE {self.exclusion.value}"

        def as_sql(self, compiler, connection):
            connection.ops.check_expression_support(self)
            start, end = self.window_frame_start_end(
                connection, self.start.value, self.end.value
            )
            if self.exclusion and not connection.features.supports_frame_exclusion:
                raise NotSupportedError(
                    "This backend does not support window frame exclusions."
                )
            return (
                self.template
                % {
                    "frame_type": self.frame_type,
                    "start": start,
                    "end": end,
                    "exclude": self.get_exclusion(),
                },
                [],
            )

        def __repr__(self):
            return "<%s: %s>" % (self.__class__.__name__, self)

        def get_group_by_cols(self):
            return []

        def __str__(self):
            if self.start.value is not None and self.start.value < 0:
                start = "%d %s" % (abs(self.start.value), connection.ops.PRECEDING)
            elif self.start.value is not None and self.start.value == 0:
                start = connection.ops.CURRENT_ROW
            elif self.start.value is not None and self.start.value > 0:
                start = "%d %s" % (self.start.value, connection.ops.FOLLOWING)
            else:
                start = connection.ops.UNBOUNDED_PRECEDING

            if self.end.value is not None and self.end.value > 0:
                end = "%d %s" % (self.end.value, connection.ops.FOLLOWING)
            elif self.end.value is not None and self.end.value == 0:
                end = connection.ops.CURRENT_ROW
            elif self.end.value is not None and self.end.value < 0:
                end = "%d %s" % (abs(self.end.value), connection.ops.PRECEDING)
            else:
                end = connection.ops.UNBOUNDED_FOLLOWING
            return self.template % {
                "frame_type": self.frame_type,
                "start": start,
                "end": end,
                "exclude": self.get_exclusion(),
            }

        def window_frame_start_end(self, connection, start, end):
            raise NotImplementedError("Subclasses must implement window_frame_start_end().")

    class RowRange(WindowFrame):
        frame_type = "ROWS"

        def window_frame_start_end(self, connection, start, end):
            return connection.ops.window_frame_rows_start_end(start, end)

    class ValueRange(WindowFrame):
        frame_type = "RANGE"

        def window_frame_start_end(self, connection, start, end):
            return connection.ops.window_frame_range_start_end(start, end)