# Τεκμηρίωση του Django - 1.10.7

# PostgreSQL specific model fields

All of these fields are available from the `django.contrib.postgres.fields` module.

## `ArrayField`

class `ArrayField`(base_field, size=None, **options)

  A field for storing lists of data. Most field types can be used, you simply pass another field instance as the `base_field`. You may also specify a `size`. `ArrayField` can be nested to store multi-dimensional arrays.

  If you give the field a `default`, ensure it’s a callable such as `list` (for an empty default) or a callable that returns a list (such as a function). Incorrectly using `default=[]` creates a mutable default that is shared between all instances of `ArrayField`.

  `base_field`

    This is a required argument.

    Specifies the underlying data type and behavior for the array. It should be an instance of a subclass of `Field`. For example, it could be an `IntegerField` or a `CharField`. Most field types are permitted, with the exception of those handling relational data (`ForeignKey`, `OneToOneField` and `ManyToManyField`).

    It is possible to nest array fields - you can specify an instance of `ArrayField` as the `base_field`. For example:

        from django.db import models
        from django.contrib.postgres.fields import ArrayField

        class ChessBoard(models.Model):
            board = ArrayField(
                ArrayField(
                    models.CharField(max_length=10, blank=True),
                    size=8,
                ),
                size=8,
            )

    Transformation of values between the database and the model, validation of data and configuration, and serialization are all delegated to the underlying base field.

  `size`

    This is an optional argument.

    If passed, the array will have a maximum size as specified. This will be passed to the database, although PostgreSQL at present does not enforce the restriction.

Σημείωση

When nesting `ArrayField`, whether you use the size parameter or not, PostgreSQL requires that the arrays are rectangular:

    from django.contrib.postgres.fields import ArrayField
    from django.db import models

    class Board(models.Model):
        pieces = ArrayField(ArrayField(models.IntegerField()))

    # Valid
    Board(pieces=[
        [2, 3],
        [2, 1],
    ])

    # Not valid
    Board(pieces=[
        [2, 3],
        [2],
    ])

If irregular shapes are required, then the underlying field should be made nullable and the values padded with `None`.

### Querying `ArrayField`

There are a number of custom lookups and transforms for `ArrayField`. We will use the following example model:

    from django.db import models
    from django.contrib.postgres.fields import ArrayField

    class Post(models.Model):
        name = models.CharField(max_length=200)
        tags = ArrayField(models.CharField(max_length=200), blank=True)

        def __str__(self):  # __unicode__ on Python 2
            return self.name

#### `contains`

The `contains` lookup is overridden on `ArrayField`. The returned objects will be those where the values passed are a subset of the data. It uses the SQL operator `@>`. For example:

    >>> Post.objects.create(name='First post', tags=['thoughts', 'django'])
    >>> Post.objects.create(name='Second post', tags=['thoughts'])
    >>> Post.objects.create(name='Third post', tags=['tutorial', 'django'])

    >>> Post.objects.filter(tags__contains=['thoughts'])
    <QuerySet [<Post: First post>, <Post: Second post>]>

    >>> Post.objects.filter(tags__contains=['django'])
    <QuerySet [<Post: First post>, <Post: Third post>]>

    >>> Post.objects.filter(tags__contains=['django', 'thoughts'])
    <QuerySet [<Post: First post>]>

#### `contained_by`

This is the inverse of the `contains` lookup - the objects returned will be those where the data is a subset of the values passed. It uses the SQL operator `<@`. For example:

    >>> Post.objects.create(name='First post', tags=['thoughts', 'django'])
    >>> Post.objects.create(name='Second post', tags=['thoughts'])
    >>> Post.objects.create(name='Third post', tags=['tutorial', 'django'])

    >>> Post.objects.filter(tags__contained_by=['thoughts', 'django'])
    <QuerySet [<Post: First post>, <Post: Second post>]>

    >>> Post.objects.filter(tags__contained_by=['thoughts', 'django', 'tutorial'])
    <QuerySet [<Post: First post>, <Post: Second post>, <Post: Third post>]>

#### `overlap`

Returns objects where the data shares any results with the values passed. Uses the SQL operator `&&`. For example:

    >>> Post.objects.create(name='First post', tags=['thoughts', 'django'])
    >>> Post.objects.create(name='Second post', tags=['thoughts'])
    >>> Post.objects.create(name='Third post', tags=['tutorial', 'django'])

    >>> Post.objects.filter(tags__overlap=['thoughts'])
    <QuerySet [<Post: First post>, <Post: Second post>]>

    >>> Post.objects.filter(tags__overlap=['thoughts', 'tutorial'])
    <QuerySet [<Post: First post>, <Post: Second post>, <Post: Third post>]>

#### `len`

Returns the length of the array. The lookups available afterwards are those available for `IntegerField`. For example:

    >>> Post.objects.create(name='First post', tags=['thoughts', 'django'])
    >>> Post.objects.create(name='Second post', tags=['thoughts'])

    >>> Post.objects.filter(tags__len=1)
    <QuerySet [<Post: Second post>]>

#### Index transforms

This class of transforms allows you to index into the array in queries. Any non-negative integer can be used. There are no errors if it exceeds the `size` of the array. The lookups available after the transform are those from the `base_field`. For example:

    >>> Post.objects.create(name='First post', tags=['thoughts', 'django'])
    >>> Post.objects.create(name='Second post', tags=['thoughts'])

    >>> Post.objects.filter(tags__0='thoughts')
    <QuerySet [<Post: First post>, <Post: Second post>]>

    >>> Post.objects.filter(tags__1__iexact='Django')
    <QuerySet [<Post: First post>]>

    >>> Post.objects.filter(tags__276='javascript')
    <QuerySet []>

Σημείωση

PostgreSQL uses 1-based indexing for array fields when writing raw SQL. However these indexes and those used in `slices` use 0-based indexing to be consistent with Python.

#### Slice transforms

This class of transforms allow you to take a slice of the array. Any two non-negative integers can be used, separated by a single underscore. The lookups available after the transform do not change. For example:

    >>> Post.objects.create(name='First post', tags=['thoughts', 'django'])
    >>> Post.objects.create(name='Second post', tags=['thoughts'])
    >>> Post.objects.create(name='Third post', tags=['django', 'python', 'thoughts'])

    >>> Post.objects.filter(tags__0_1=['thoughts'])
    <QuerySet [<Post: First post>, <Post: Second post>]>

    >>> Post.objects.filter(tags__0_2__contains=['thoughts'])
    <QuerySet [<Post: First post>, <Post: Second post>]>

Σημείωση

PostgreSQL uses 1-based indexing for array fields when writing raw SQL. However these slices and those used in `indexes` use 0-based indexing to be consistent with Python.

Multidimensional arrays with indexes and slices

PostgreSQL has some rather esoteric behavior when using indexes and slices on multidimensional arrays. It will always work to use indexes to reach down to the final underlying data, but most other slices behave strangely at the database level and cannot be supported in a logical, consistent fashion by Django.

### Indexing `ArrayField`

At present using `db_index` will create a `btree` index. This does not offer particularly significant help to querying. A more useful index is a `GIN` index, which you should create using a `RunSQL` operation.

## `HStoreField`

class `HStoreField`(**options)

  A field for storing mappings of strings to strings. The Python data type used is a `dict`.

  To use this field, you’ll need to:

  1. Add `'django.contrib.postgres'` in your `INSTALLED_APPS`.
  2. Setup the hstore extension in PostgreSQL.

  You’ll see an error like `can't adapt type 'dict'` if you skip the first step, or `type "hstore" does not exist` if you skip the second.

Σημείωση

On occasions it may be useful to require or restrict the keys which are valid for a given field. This can be done using the `KeysValidator`.

### Querying `HStoreField`

In addition to the ability to query by key, there are a number of custom lookups available for `HStoreField`.

We will use the following example model:

    from django.contrib.postgres.fields import HStoreField
    from django.db import models

    class Dog(models.Model):
        name = models.CharField(max_length=200)
        data = HStoreField()

        def __str__(self):  # __unicode__ on Python 2
            return self.name

#### Key lookups

To query based on a given key, you simply use that key as the lookup name:

    >>> Dog.objects.create(name='Rufus', data={'breed': 'labrador'})
    >>> Dog.objects.create(name='Meg', data={'breed': 'collie'})

    >>> Dog.objects.filter(data__breed='collie')
    <QuerySet [<Dog: Meg>]>

You can chain other lookups after key lookups:

    >>> Dog.objects.filter(data__breed__contains='l')
    <QuerySet [<Dog: Rufus>, <Dog: Meg>]>

If the key you wish to query by clashes with the name of another lookup, you need to use the `hstorefield.contains` lookup instead.

Προειδοποίηση

Since any string could be a key in a hstore value, any lookup other than those listed below will be interpreted as a key lookup. No errors are raised. Be extra careful for typing mistakes, and always check your queries work as you intend.

#### `contains`

The `contains` lookup is overridden on `HStoreField`. The returned objects are those where the given `dict` of key-value pairs are all contained in the field. It uses the SQL operator `@>`. For example:

    >>> Dog.objects.create(name='Rufus', data={'breed': 'labrador', 'owner': 'Bob'})
    >>> Dog.objects.create(name='Meg', data={'breed': 'collie', 'owner': 'Bob'})
    >>> Dog.objects.create(name='Fred', data={})

    >>> Dog.objects.filter(data__contains={'owner': 'Bob'})
    <QuerySet [<Dog: Rufus>, <Dog: Meg>]>

    >>> Dog.objects.filter(data__contains={'breed': 'collie'})
    <QuerySet [<Dog: Meg>]>

#### `contained_by`

This is the inverse of the `contains` lookup - the objects returned will be those where the key-value pairs on the object are a subset of those in the value passed. It uses the SQL operator `<@`. For example:

    >>> Dog.objects.create(name='Rufus', data={'breed': 'labrador', 'owner': 'Bob'})
    >>> Dog.objects.create(name='Meg', data={'breed': 'collie', 'owner': 'Bob'})
    >>> Dog.objects.create(name='Fred', data={})

    >>> Dog.objects.filter(data__contained_by={'breed': 'collie', 'owner': 'Bob'})
    <QuerySet [<Dog: Meg>, <Dog: Fred>]>

    >>> Dog.objects.filter(data__contained_by={'breed': 'collie'})
    <QuerySet [<Dog: Fred>]>

#### `has_key`

Returns objects where the given key is in the data. Uses the SQL operator `?`. For example:

    >>> Dog.objects.create(name='Rufus', data={'breed': 'labrador'})
    >>> Dog.objects.create(name='Meg', data={'breed': 'collie', 'owner': 'Bob'})

    >>> Dog.objects.filter(data__has_key='owner')
    <QuerySet [<Dog: Meg>]>

#### `has_any_keys`

Returns objects where any of the given keys are in the data. Uses the SQL operator `?|`. For example:

    >>> Dog.objects.create(name='Rufus', data={'breed': 'labrador'})
    >>> Dog.objects.create(name='Meg', data={'owner': 'Bob'})
    >>> Dog.objects.create(name='Fred', data={})

    >>> Dog.objects.filter(data__has_any_keys=['owner', 'breed'])
    <QuerySet [<Dog: Rufus>, <Dog: Meg>]>

#### `has_keys`

Returns objects where all of the given keys are in the data. Uses the SQL operator `?&`. For example:

    >>> Dog.objects.create(name='Rufus', data={})
    >>> Dog.objects.create(name='Meg', data={'breed': 'collie', 'owner': 'Bob'})

    >>> Dog.objects.filter(data__has_keys=['breed', 'owner'])
    <QuerySet [<Dog: Meg>]>

#### `keys`

Returns objects where the array of keys is the given value. Note that the order is not guaranteed to be reliable, so this transform is mainly useful for using in conjunction with lookups on `ArrayField`. Uses the SQL function `akeys()`. For example:

    >>> Dog.objects.create(name='Rufus', data={'toy': 'bone'})
    >>> Dog.objects.create(name='Meg', data={'breed': 'collie', 'owner': 'Bob'})

    >>> Dog.objects.filter(data__keys__overlap=['breed', 'toy'])
    <QuerySet [<Dog: Rufus>, <Dog: Meg>]>

#### `values`

Returns objects where the array of values is the given value. Note that the order is not guaranteed to be reliable, so this transform is mainly useful for using in conjunction with lookups on `ArrayField`. Uses the SQL function `avalues()`. For example:

    >>> Dog.objects.create(name='Rufus', data={'breed': 'labrador'})
    >>> Dog.objects.create(name='Meg', data={'breed': 'collie', 'owner': 'Bob'})

    >>> Dog.objects.filter(data__values__contains=['collie'])
    <QuerySet [<Dog: Meg>]>

## `JSONField`

class `JSONField`(**options)

  A field for storing JSON encoded data. In Python the data is represented in its Python native format: dictionaries, lists, strings, numbers, booleans and `None`.

  If you want to store other data types, you’ll need to serialize them first. For example, you might cast a `datetime` to a string. You might also want to convert the string back to a `datetime` when you retrieve the data from the database. There are some third-party `JSONField` implementations which do this sort of thing automatically.

  If you give the field a `default`, ensure it’s a callable such as `dict` (for an empty default) or a callable that returns a dict (such as a function). Incorrectly using `default={}` creates a mutable default that is shared between all instances of `JSONField`.

Σημείωση

PostgreSQL has two native JSON based data types: `json` and `jsonb`. The main difference between them is how they are stored and how they can be queried. PostgreSQL’s `json` field is stored as the original string representation of the JSON and must be decoded on the fly when queried based on keys. The `jsonb` field is stored based on the actual structure of the JSON which allows indexing. The trade-off is a small additional cost on writing to the `jsonb` field. `JSONField` uses `jsonb`.

As a result, this field requires PostgreSQL ≥ 9.4 and Psycopg2 ≥ 2.5.4.

### Querying `JSONField`

We will use the following example model:

    from django.contrib.postgres.fields import JSONField
    from django.db import models

    class Dog(models.Model):
        name = models.CharField(max_length=200)
        data = JSONField()

        def __str__(self):  # __unicode__ on Python 2
            return self.name

#### Key, index, and path lookups

To query based on a given dictionary key, simply use that key as the lookup name:

    >>> Dog.objects.create(name='Rufus', data={
    ...     'breed': 'labrador',
    ...     'owner': {
    ...         'name': 'Bob',
    ...         'other_pets': [{
    ...             'name': 'Fishy',
    ...         }],
    ...     },
    ... })
    >>> Dog.objects.create(name='Meg', data={'breed': 'collie'})

    >>> Dog.objects.filter(data__breed='collie')
    <QuerySet [<Dog: Meg>]>

Multiple keys can be chained together to form a path lookup:

    >>> Dog.objects.filter(data__owner__name='Bob')
    <QuerySet [<QuerySet <Dog: Rufus>]>

If the key is an integer, it will be interpreted as an index lookup in an array:

    >>> Dog.objects.filter(data__owner__other_pets__0__name='Fishy')
    <QuerySet [<Dog: Rufus>]>

If the key you wish to query by clashes with the name of another lookup, use the `jsonfield.contains` lookup instead.

If only one key or index is used, the SQL operator `->` is used. If multiple operators are used then the `#>` operator is used.

Προειδοποίηση

Since any string could be a key in a JSON object, any lookup other than those listed below will be interpreted as a key lookup. No errors are raised. Be extra careful for typing mistakes, and always check your queries work as you intend.

#### Containment and key operations

`JSONField` shares lookups relating to containment and keys with `HStoreField`.

- `contains` (accepts any JSON rather than just a dictionary of strings)
- `contained_by` (accepts any JSON rather than just a dictionary of strings)
- `has_key`
- `has_any_keys`
- `has_keys`

## Range Fields

There are five range field types, corresponding to the built-in range types in PostgreSQL. These fields are used to store a range of values; for example the start and end timestamps of an event, or the range of ages an activity is suitable for.

All of the range fields translate to psycopg2 Range objects in python, but also accept tuples as input if no bounds information is necessary. The default is lower bound included, upper bound excluded; that is, `[)`.

### `IntegerRangeField`

class `IntegerRangeField`(**options)

  Stores a range of integers. Based on an `IntegerField`. Represented by an `int4range` in the database and a `NumericRange` in Python.

  Regardless of the bounds specified when saving the data, PostgreSQL always returns a range in a canonical form that includes the lower bound and excludes the upper bound; that is `[)`.

### `BigIntegerRangeField`

class `BigIntegerRangeField`(**options)

  Stores a range of large integers. Based on a `BigIntegerField`. Represented by an `int8range` in the database and a `NumericRange` in Python.

  Regardless of the bounds specified when saving the data, PostgreSQL always returns a range in a canonical form that includes the lower bound and excludes the upper bound; that is `[)`.

### `FloatRangeField`

class `FloatRangeField`(**options)

  Stores a range of floating point values. Based on a `FloatField`. Represented by a `numrange` in the database and a `NumericRange` in Python.

### `DateTimeRangeField`

class `DateTimeRangeField`(**options)

  Stores a range of timestamps. Based on a `DateTimeField`. Represented by a `tztsrange` in the database and a `DateTimeTZRange` in Python.

### `DateRangeField`

class `DateRangeField`(**options)

  Stores a range of dates. Based on a `DateField`. Represented by a `daterange` in the database and a `DateRange` in Python.

  Regardless of the bounds specified when saving the data, PostgreSQL always returns a range in a canonical form that includes the lower bound and excludes the upper bound; that is `[)`.

### Querying Range Fields

There are a number of custom lookups and transforms for range fields. They are available on all the above fields, but we will use the following example model:

    from django.contrib.postgres.fields import IntegerRangeField
    from django.db import models

    class Event(models.Model):
        name = models.CharField(max_length=200)
        ages = IntegerRangeField()
        start = models.DateTimeField()

        def __str__(self):  # __unicode__ on Python 2
            return self.name

We will also use the following example objects:

    >>> import datetime
    >>> from django.utils import timezone
    >>> now = timezone.now()
    >>> Event.objects.create(name='Soft play', ages=(0, 10), start=now)
    >>> Event.objects.create(name='Pub trip', ages=(21, None), start=now - datetime.timedelta(days=1))

and `NumericRange`:

    >>> from psycopg2.extras import NumericRange

#### Containment functions

As with other PostgreSQL fields, there are three standard containment operators: `contains`, `contained_by` and `overlap`, using the SQL operators `@>`, `<@`, and `&&` respectively.

##### `contains`

    >>> Event.objects.filter(ages__contains=NumericRange(4, 5))
    <QuerySet [<Event: Soft play>]>

##### `contained_by`

    >>> Event.objects.filter(ages__contained_by=NumericRange(0, 15))
    <QuerySet [<Event: Soft play>]>

The `contained_by` lookup is also available on the non-range field types: `IntegerField`, `BigIntegerField`, `FloatField`, `DateField`, and `DateTimeField`. For example:

    >>> from psycopg2.extras import DateTimeTZRange
    >>> Event.objects.filter(start__contained_by=DateTimeTZRange(
    ...     timezone.now() - datetime.timedelta(hours=1),
    ...     timezone.now() + datetime.timedelta(hours=1),
    ... )
    <QuerySet [<Event: Soft play>]>

##### `overlap`

    >>> Event.objects.filter(ages__overlap=NumericRange(8, 12))
    <QuerySet [<Event: Soft play>]>

#### Comparison functions

Range fields support the standard lookups: `lt`, `gt`, `lte` and `gte`. These are not particularly helpful - they compare the lower bounds first and then the upper bounds only if necessary. This is also the strategy used to order by a range field. It is better to use the specific range comparison operators.

##### `fully_lt`

The returned ranges are strictly less than the passed range. In other words, all the points in the returned range are less than all those in the passed range.

    >>> Event.objects.filter(ages__fully_lt=NumericRange(11, 15))
    <QuerySet [<Event: Soft play>]>

##### `fully_gt`

The returned ranges are strictly greater than the passed range. In other words, the all the points in the returned range are greater than all those in the passed range.

    >>> Event.objects.filter(ages__fully_gt=NumericRange(11, 15))
    <QuerySet [<Event: Pub trip>]>

##### `not_lt`

The returned ranges do not contain any points less than the passed range, that is the lower bound of the returned range is at least the lower bound of the passed range.

    >>> Event.objects.filter(ages__not_lt=NumericRange(0, 15))
    <QuerySet [<Event: Soft play>, <Event: Pub trip>]>

##### `not_gt`

The returned ranges do not contain any points greater than the passed range, that is the upper bound of the returned range is at most the upper bound of the passed range.

    >>> Event.objects.filter(ages__not_gt=NumericRange(3, 10))
    <QuerySet [<Event: Soft play>]>

##### `adjacent_to`

The returned ranges share a bound with the passed range.

    >>> Event.objects.filter(ages__adjacent_to=NumericRange(10, 21))
    <QuerySet [<Event: Soft play>, <Event: Pub trip>]>

#### Querying using the bounds

There are three transforms available for use in queries. You can extract the lower or upper bound, or query based on emptiness.

##### `startswith`

Returned objects have the given lower bound. Can be chained to valid lookups for the base field.

    >>> Event.objects.filter(ages__startswith=21)
    <QuerySet [<Event: Pub trip>]>

##### `endswith`

Returned objects have the given upper bound. Can be chained to valid lookups for the base field.

    >>> Event.objects.filter(ages__endswith=10)
    <QuerySet [<Event: Soft play>]>

##### `isempty`

Returned objects are empty ranges. Can be chained to valid lookups for a `BooleanField`.

    >>> Event.objects.filter(ages__isempty=True)
    <QuerySet []>

#### Defining your own range types

PostgreSQL allows the definition of custom range types. Django’s model and form field implementations use base classes below, and psycopg2 provides a `register_range()` to allow use of custom range types.

class `RangeField`(**options)

  Base class for model range fields.

  `base_field`

    The model field class to use.

  `range_type`

    The psycopg2 range type to use.

  `form_field`

    The form field class to use. Should be a subclass of `django.contrib.postgres.forms.BaseRangeField`.

class `django.contrib.postgres.forms.``BaseRangeField`

  Base class for form range fields.

  `base_field`

    The form field to use.

  `range_type`

    The psycopg2 range type to use.