# Τεκμηρίωση του Django - 1.10.7

# Πηγαίος κώδικας για το django.contrib.postgres.search

    from django.db.models import Field, FloatField
    from django.db.models.expressions import CombinedExpression, Func, Value
    from django.db.models.functions import Coalesce
    from django.db.models.lookups import Lookup

    class SearchVectorExact(Lookup):
        lookup_name = 'exact'

        def process_rhs(self, qn, connection):
            if not hasattr(self.rhs, 'resolve_expression'):
                config = getattr(self.lhs, 'config', None)
                self.rhs = SearchQuery(self.rhs, config=config)
            rhs, rhs_params = super(SearchVectorExact, self).process_rhs(qn, connection)
            return rhs, rhs_params

        def as_sql(self, qn, connection):
            lhs, lhs_params = self.process_lhs(qn, connection)
            rhs, rhs_params = self.process_rhs(qn, connection)
            params = lhs_params + rhs_params
            return '%s @@ %s = true' % (lhs, rhs), params

    class SearchVectorField(Field):

        def db_type(self, connection):
            return 'tsvector'

    class SearchQueryField(Field):

        def db_type(self, connection):
            return 'tsquery'

    class SearchVectorCombinable(object):
        ADD = '||'

        def _combine(self, other, connector, reversed, node=None):
            if not isinstance(other, SearchVectorCombinable) or not self.config == other.config:
                raise TypeError('SearchVector can only be combined with other SearchVectors')
            if reversed:
                return CombinedSearchVector(other, connector, self, self.config)
            return CombinedSearchVector(self, connector, other, self.config)

    class SearchVector(SearchVectorCombinable, Func):
        function = 'to_tsvector'
        arg_joiner = " || ' ' || "
        _output_field = SearchVectorField()
        config = None

        def __init__(self, *expressions, **extra):
            super(SearchVector, self).__init__(*expressions, **extra)
            self.source_expressions = [
                Coalesce(expression, Value('')) for expression in self.source_expressions
            ]
            self.config = self.extra.get('config', self.config)
            weight = self.extra.get('weight')
            if weight is not None and not hasattr(weight, 'resolve_expression'):
                weight = Value(weight)
            self.weight = weight

        def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
            resolved = super(SearchVector, self).resolve_expression(query, allow_joins, reuse, summarize, for_save)
            if self.config:
                if not hasattr(self.config, 'resolve_expression'):
                    resolved.config = Value(self.config).resolve_expression(query, allow_joins, reuse, summarize, for_save)
                else:
                    resolved.config = self.config.resolve_expression(query, allow_joins, reuse, summarize, for_save)
            return resolved

        def as_sql(self, compiler, connection, function=None, template=None):
            config_params = []
            if template is None:
                if self.config:
                    config_sql, config_params = compiler.compile(self.config)
                    template = "%(function)s({}::regconfig, %(expressions)s)".format(config_sql.replace('%', '%%'))
                else:
                    template = self.template
            sql, params = super(SearchVector, self).as_sql(compiler, connection, function=function, template=template)
            extra_params = []
            if self.weight:
                weight_sql, extra_params = compiler.compile(self.weight)
                sql = 'setweight({}, {})'.format(sql, weight_sql)
            return sql, config_params + params + extra_params

    class CombinedSearchVector(SearchVectorCombinable, CombinedExpression):
        def __init__(self, lhs, connector, rhs, config, output_field=None):
            self.config = config
            super(CombinedSearchVector, self).__init__(lhs, connector, rhs, output_field)

    class SearchQueryCombinable(object):
        BITAND = '&&'
        BITOR = '||'

        def _combine(self, other, connector, reversed, node=None):
            if not isinstance(other, SearchQueryCombinable):
                raise TypeError(
                    'SearchQuery can only be combined with other SearchQuerys, '
                    'got {}.'.format(type(other))
                )
            if not self.config == other.config:
                raise TypeError("SearchQuery configs don't match.")
            if reversed:
                return CombinedSearchQuery(other, connector, self, self.config)
            return CombinedSearchQuery(self, connector, other, self.config)

        # On Combinable, these are not implemented to reduce confusion with Q. In
        # this case we are actually (ab)using them to do logical combination so
        # it's consistent with other usage in Django.
        def __or__(self, other):
            return self._combine(other, self.BITOR, False)

        def __ror__(self, other):
            return self._combine(other, self.BITOR, True)

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

        def __rand__(self, other):
            return self._combine(other, self.BITAND, True)

    class SearchQuery(SearchQueryCombinable, Value):
        invert = False
        _output_field = SearchQueryField()
        config = None

        def __init__(self, value, output_field=None, **extra):
            self.config = extra.pop('config', self.config)
            self.invert = extra.pop('invert', self.invert)
            super(SearchQuery, self).__init__(value, output_field=output_field)

        def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
            resolved = super(SearchQuery, self).resolve_expression(query, allow_joins, reuse, summarize, for_save)
            if self.config:
                if not hasattr(self.config, 'resolve_expression'):
                    resolved.config = Value(self.config).resolve_expression(query, allow_joins, reuse, summarize, for_save)
                else:
                    resolved.config = self.config.resolve_expression(query, allow_joins, reuse, summarize, for_save)
            return resolved

        def as_sql(self, compiler, connection):
            params = [self.value]
            if self.config:
                config_sql, config_params = compiler.compile(self.config)
                template = 'plainto_tsquery({}::regconfig, %s)'.format(config_sql)
                params = config_params + [self.value]
            else:
                template = 'plainto_tsquery(%s)'
            if self.invert:
                template = '!!({})'.format(template)
            return template, params

        def _combine(self, other, connector, reversed, node=None):
            combined = super(SearchQuery, self)._combine(other, connector, reversed, node)
            combined.output_field = SearchQueryField()
            return combined

        def __invert__(self):
            extra = {
                'invert': not self.invert,
                'config': self.config,
            }
            return type(self)(self.value, **extra)

    class CombinedSearchQuery(SearchQueryCombinable, CombinedExpression):
        def __init__(self, lhs, connector, rhs, config, output_field=None):
            self.config = config
            super(CombinedSearchQuery, self).__init__(lhs, connector, rhs, output_field)

    class SearchRank(Func):
        function = 'ts_rank'
        _output_field = FloatField()

        def __init__(self, vector, query, **extra):
            if not hasattr(vector, 'resolve_expression'):
                vector = SearchVector(vector)
            if not hasattr(query, 'resolve_expression'):
                query = SearchQuery(query)
            weights = extra.get('weights')
            if weights is not None and not hasattr(weights, 'resolve_expression'):
                weights = Value(weights)
            self.weights = weights
            super(SearchRank, self).__init__(vector, query, **extra)

        def as_sql(self, compiler, connection, function=None, template=None):
            extra_params = []
            extra_context = {}
            if template is None and self.extra.get('weights'):
                if self.weights:
                    template = '%(function)s(%(weights)s, %(expressions)s)'
                    weight_sql, extra_params = compiler.compile(self.weights)
                    extra_context['weights'] = weight_sql
            sql, params = super(SearchRank, self).as_sql(
                compiler, connection,
                function=function, template=template, **extra_context
            )
            return sql, extra_params + params

    SearchVectorField.register_lookup(SearchVectorExact)

    class TrigramBase(Func):
        def __init__(self, expression, string, **extra):
            if not hasattr(string, 'resolve_expression'):
                string = Value(string)
            super(TrigramBase, self).__init__(expression, string, output_field=FloatField(), **extra)

    class TrigramSimilarity(TrigramBase):
        function = 'SIMILARITY'

    class TrigramDistance(TrigramBase):
        function = ''
        arg_joiner = ' <-> '