django/docs/ref/contrib/postgres/fields.txt

================================
PostgreSQL specific model fields
================================

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

.. currentmodule:: django.contrib.postgres.fields

``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 :attr:`base_field
    <ArrayField.base_field>`. You may also specify a :attr:`size
    <ArrayField.size>`. ``ArrayField`` can be nested to store multi-dimensional
    arrays.

    If you give the field a :attr:`~django.db.models.Field.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``.

    .. attribute:: 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
        :class:`~django.db.models.Field`. For example, it could be an
        :class:`~django.db.models.IntegerField` or a
        :class:`~django.db.models.CharField`. Most field types are permitted,
        with the exception of those handling relational data
        (:class:`~django.db.models.ForeignKey`,
        :class:`~django.db.models.OneToOneField` and
        :class:`~django.db.models.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.

    .. attribute:: 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.

.. note::

    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 :class:`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):
            return self.name

.. fieldlookup:: arrayfield.contains

``contains``
~~~~~~~~~~~~

The :lookup:`contains` lookup is overridden on :class:`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>]>

.. fieldlookup:: arrayfield.contained_by

``contained_by``
~~~~~~~~~~~~~~~~

This is the inverse of the :lookup:`contains <arrayfield.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>]>

.. fieldlookup:: arrayfield.overlap

``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>]>

.. fieldlookup:: arrayfield.len

``len``
~~~~~~~

Returns the length of the array. The lookups available afterwards are those
available for :class:`~django.db.models.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>]>

.. fieldlookup:: arrayfield.index

Index transforms
~~~~~~~~~~~~~~~~

Index transforms index into the array. Any non-negative integer can be used.
There are no errors if it exceeds the :attr:`size <ArrayField.size>` of the
array. The lookups available after the transform are those from the
:attr:`base_field <ArrayField.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 []>

.. note::

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

.. fieldlookup:: arrayfield.slice

Slice transforms
~~~~~~~~~~~~~~~~

Slice transforms 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>]>

.. note::

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

.. admonition:: 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 :attr:`~django.db.models.Field.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
:class:`~django.db.migrations.operations.RunSQL` operation.

``CIText`` fields
=================

.. class:: CIText(**options)

    A mixin to create case-insensitive text fields backed by the citext_ type.
    Read about `the performance considerations`_ prior to using it.

    To use ``citext``, use the :class:`.CITextExtension` operation to
    :ref:`setup the citext extension <create-postgresql-extensions>` in
    PostgreSQL before the first ``CreateModel`` migration operation.

    Several fields that use the mixin are provided:

.. class:: CICharField(**options)
.. class:: CIEmailField(**options)
.. class:: CITextField(**options)

    These fields subclass :class:`~django.db.models.CharField`,
    :class:`~django.db.models.EmailField`, and
    :class:`~django.db.models.TextField`, respectively.

    ``max_length`` won't be enforced in the database since ``citext`` behaves
    similar to PostgreSQL's ``text`` type.

    .. _citext: https://www.postgresql.org/docs/current/static/citext.html
    .. _the performance considerations: https://www.postgresql.org/docs/current/static/citext.html#AEN178177

``HStoreField``
===============

.. class:: HStoreField(**options)

    A field for storing key-value pairs. The Python data type used is a
    ``dict``. Keys must be strings, and values may be either strings or nulls
    (``None`` in Python).

    To use this field, you'll need to:

    1. Add ``'django.contrib.postgres'`` in your :setting:`INSTALLED_APPS`.
    2. :ref:`Setup the hstore extension <create-postgresql-extensions>` 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.

.. note::

    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
    :class:`~django.contrib.postgres.validators.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):
            return self.name

.. fieldlookup:: hstorefield.key

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 :lookup:`hstorefield.contains` lookup instead.

.. warning::

    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.

.. fieldlookup:: hstorefield.contains

``contains``
~~~~~~~~~~~~

The :lookup:`contains` lookup is overridden on
:class:`~django.contrib.postgres.fields.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>]>

.. fieldlookup:: hstorefield.contained_by

``contained_by``
~~~~~~~~~~~~~~~~

This is the inverse of the :lookup:`contains <hstorefield.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>]>

.. fieldlookup:: hstorefield.has_key

``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>]>

.. fieldlookup:: hstorefield.has_any_keys

``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>]>

.. fieldlookup:: hstorefield.has_keys

``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>]>

.. fieldlookup:: hstorefield.keys

``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
:class:`~django.contrib.postgres.fields.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>]>

.. fieldlookup:: hstorefield.values

``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
:class:`~django.contrib.postgres.fields.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(encoder=None, **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``.

    .. attribute:: encoder

        An optional JSON-encoding class to serialize data types not supported
        by the standard JSON serializer (``datetime``, ``uuid``, etc.). For
        example, you can use the
        :class:`~django.core.serializers.json.DjangoJSONEncoder` class or any
        other :py:class:`json.JSONEncoder` subclass.

        When the value is retrieved from the database, it will be in the format
        chosen by the custom encoder (most often a string), so you'll need to
        take extra steps to convert the value back to the initial data type
        (:meth:`Model.from_db() <django.db.models.Model.from_db>` and
        :meth:`Field.from_db_value() <django.db.models.Field.from_db_value>`
        are two possible hooks for that purpose). Your deserialization may need
        to account for the fact that you can't be certain of the input type.
        For example, you run the risk of returning a ``datetime`` that was
        actually a string that just happened to be in the same format chosen
        for ``datetime``\s.

    If you give the field a :attr:`~django.db.models.Field.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``.

.. note::

    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``.

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):
            return self.name

.. fieldlookup:: jsonfield.key

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 [<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 :lookup:`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.

.. warning::

    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
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. fieldlookup:: jsonfield.contains
.. fieldlookup:: jsonfield.contained_by
.. fieldlookup:: jsonfield.has_key
.. fieldlookup:: jsonfield.has_any_keys
.. fieldlookup:: jsonfield.has_keys

:class:`~django.contrib.postgres.fields.JSONField` shares lookups relating to
containment and keys with :class:`~django.contrib.postgres.fields.HStoreField`.

- :lookup:`contains <hstorefield.contains>` (accepts any JSON rather than
  just a dictionary of strings)
- :lookup:`contained_by <hstorefield.contained_by>` (accepts any JSON
  rather than just a dictionary of strings)
- :lookup:`has_key <hstorefield.has_key>`
- :lookup:`has_any_keys <hstorefield.has_any_keys>`
- :lookup:`has_keys <hstorefield.has_keys>`

.. _range-fields:

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 :ref:`psycopg2 Range objects
<psycopg2:adapt-range>` 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
    :class:`~django.db.models.IntegerField`. Represented by an ``int4range`` in
    the database and a :class:`~psycopg2:psycopg2.extras.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
    :class:`~django.db.models.BigIntegerField`. Represented by an ``int8range``
    in the database and a :class:`~psycopg2:psycopg2.extras.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
    :class:`~django.db.models.FloatField`. Represented by a ``numrange`` in the
    database and a :class:`~psycopg2:psycopg2.extras.NumericRange` in Python.

``DateTimeRangeField``
----------------------

.. class:: DateTimeRangeField(**options)

    Stores a range of timestamps. Based on a
    :class:`~django.db.models.DateTimeField`. Represented by a ``tstzrange`` in
    the database and a :class:`~psycopg2:psycopg2.extras.DateTimeTZRange` in
    Python.

``DateRangeField``
------------------

.. class:: DateRangeField(**options)

    Stores a range of dates. Based on a
    :class:`~django.db.models.DateField`. Represented by a ``daterange`` in the
    database and a :class:`~psycopg2:psycopg2.extras.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):
            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.

.. fieldlookup:: rangefield.contains

``contains``
^^^^^^^^^^^^

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

.. fieldlookup:: rangefield.contained_by

``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:
:class:`~django.db.models.IntegerField`,
:class:`~django.db.models.BigIntegerField`,
:class:`~django.db.models.FloatField`, :class:`~django.db.models.DateField`,
and :class:`~django.db.models.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>]>

.. fieldlookup:: rangefield.overlap

``overlap``
^^^^^^^^^^^

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

Comparison functions
~~~~~~~~~~~~~~~~~~~~

Range fields support the standard lookups: :lookup:`lt`, :lookup:`gt`,
:lookup:`lte` and :lookup:`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.

.. fieldlookup:: rangefield.fully_lt

``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>]>

.. fieldlookup:: rangefield.fully_gt

``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>]>

.. fieldlookup:: rangefield.not_lt

``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>]>

.. fieldlookup:: rangefield.not_gt

``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>]>

.. fieldlookup:: rangefield.adjacent_to

``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.

.. fieldlookup:: rangefield.startswith

``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>]>

.. fieldlookup:: rangefield.endswith

``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>]>

.. fieldlookup:: rangefield.isempty

``isempty``
^^^^^^^^^^^

Returned objects are empty ranges. Can be chained to valid lookups for a
:class:`~django.db.models.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
:func:`~psycopg2:psycopg2.extras.register_range` to allow use of custom range
types.

.. class:: RangeField(**options)

    Base class for model range fields.

    .. attribute:: base_field

        The model field class to use.

    .. attribute:: range_type

        The psycopg2 range type to use.

    .. attribute:: form_field

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

.. class:: django.contrib.postgres.forms.BaseRangeField

    Base class for form range fields.

    .. attribute:: base_field

        The form field to use.

    .. attribute:: range_type

        The psycopg2 range type to use.