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698 lines
21 KiB
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698 lines
21 KiB
Plaintext
PostgreSQL specific model fields
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================================
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All of these fields are available from the ``django.contrib.postgres.fields``
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module.
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.. currentmodule:: django.contrib.postgres.fields
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ArrayField
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----------
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.. class:: ArrayField(base_field, size=None, **options)
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A field for storing lists of data. Most field types can be used, you simply
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pass another field instance as the :attr:`base_field
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<ArrayField.base_field>`. You may also specify a :attr:`size
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<ArrayField.size>`. ``ArrayField`` can be nested to store multi-dimensional
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arrays.
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.. attribute:: base_field
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This is a required argument.
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Specifies the underlying data type and behavior for the array. It
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should be an instance of a subclass of
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:class:`~django.db.models.Field`. For example, it could be an
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:class:`~django.db.models.IntegerField` or a
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:class:`~django.db.models.CharField`. Most field types are permitted,
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with the exception of those handling relational data
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(:class:`~django.db.models.ForeignKey`,
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:class:`~django.db.models.OneToOneField` and
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:class:`~django.db.models.ManyToManyField`).
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It is possible to nest array fields - you can specify an instance of
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``ArrayField`` as the ``base_field``. For example::
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from django.db import models
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from django.contrib.postgres.fields import ArrayField
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class ChessBoard(models.Model):
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board = ArrayField(
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ArrayField(
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models.CharField(max_length=10, blank=True),
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size=8,
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),
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size=8,
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)
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Transformation of values between the database and the model, validation
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of data and configuration, and serialization are all delegated to the
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underlying base field.
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.. attribute:: size
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This is an optional argument.
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If passed, the array will have a maximum size as specified. This will
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be passed to the database, although PostgreSQL at present does not
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enforce the restriction.
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.. note::
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When nesting ``ArrayField``, whether you use the `size` parameter or not,
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PostgreSQL requires that the arrays are rectangular::
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from django.contrib.postgres.fields import ArrayField
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from django.db import models
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class Board(models.Model):
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pieces = ArrayField(ArrayField(models.IntegerField()))
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# Valid
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Board(pieces=[
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[2, 3],
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[2, 1],
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])
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# Not valid
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Board(pieces=[
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[2, 3],
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[2],
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])
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If irregular shapes are required, then the underlying field should be made
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nullable and the values padded with ``None``.
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Querying ArrayField
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^^^^^^^^^^^^^^^^^^^
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There are a number of custom lookups and transforms for :class:`ArrayField`.
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We will use the following example model::
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from django.db import models
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from django.contrib.postgres.fields import ArrayField
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class Post(models.Model):
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name = models.CharField(max_length=200)
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tags = ArrayField(models.CharField(max_length=200), blank=True)
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def __str__(self): # __unicode__ on Python 2
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return self.name
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.. fieldlookup:: arrayfield.contains
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contains
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~~~~~~~~
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The :lookup:`contains` lookup is overridden on :class:`ArrayField`. The
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returned objects will be those where the values passed are a subset of the
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data. It uses the SQL operator ``@>``. For example::
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>>> Post.objects.create(name='First post', tags=['thoughts', 'django'])
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>>> Post.objects.create(name='Second post', tags=['thoughts'])
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>>> Post.objects.create(name='Third post', tags=['tutorial', 'django'])
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>>> Post.objects.filter(tags__contains=['thoughts'])
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[<Post: First post>, <Post: Second post>]
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>>> Post.objects.filter(tags__contains=['django'])
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[<Post: First post>, <Post: Third post>]
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>>> Post.objects.filter(tags__contains=['django', 'thoughts'])
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[<Post: First post>]
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.. fieldlookup:: arrayfield.contained_by
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contained_by
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~~~~~~~~~~~~
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This is the inverse of the :lookup:`contains <arrayfield.contains>` lookup -
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the objects returned will be those where the data is a subset of the values
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passed. It uses the SQL operator ``<@``. For example::
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>>> Post.objects.create(name='First post', tags=['thoughts', 'django'])
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>>> Post.objects.create(name='Second post', tags=['thoughts'])
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>>> Post.objects.create(name='Third post', tags=['tutorial', 'django'])
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>>> Post.objects.filter(tags__contained_by=['thoughts', 'django'])
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[<Post: First post>, <Post: Second post>]
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>>> Post.objects.filter(tags__contained_by=['thoughts', 'django', 'tutorial'])
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[<Post: First post>, <Post: Second post>, <Post: Third post>]
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.. fieldlookup:: arrayfield.overlap
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overlap
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~~~~~~~
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Returns objects where the data shares any results with the values passed. Uses
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the SQL operator ``&&``. For example::
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>>> Post.objects.create(name='First post', tags=['thoughts', 'django'])
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>>> Post.objects.create(name='Second post', tags=['thoughts'])
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>>> Post.objects.create(name='Third post', tags=['tutorial', 'django'])
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>>> Post.objects.filter(tags__overlap=['thoughts'])
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[<Post: First post>, <Post: Second post>]
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>>> Post.objects.filter(tags__overlap=['thoughts', 'tutorial'])
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[<Post: First post>, <Post: Second post>, <Post: Third post>]
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.. fieldlookup:: arrayfield.len
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len
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~~~
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Returns the length of the array. The lookups available afterwards are those
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available for :class:`~django.db.models.IntegerField`. For example::
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>>> Post.objects.create(name='First post', tags=['thoughts', 'django'])
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>>> Post.objects.create(name='Second post', tags=['thoughts'])
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>>> Post.objects.filter(tags__len=1)
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[<Post: Second post>]
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.. fieldlookup:: arrayfield.index
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Index transforms
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~~~~~~~~~~~~~~~~
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This class of transforms allows you to index into the array in queries. Any
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non-negative integer can be used. There are no errors if it exceeds the
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:attr:`size <ArrayField.size>` of the array. The lookups available after the
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transform are those from the :attr:`base_field <ArrayField.base_field>`. For
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example::
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>>> Post.objects.create(name='First post', tags=['thoughts', 'django'])
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>>> Post.objects.create(name='Second post', tags=['thoughts'])
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>>> Post.objects.filter(tags__0='thoughts')
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[<Post: First post>, <Post: Second post>]
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>>> Post.objects.filter(tags__1__iexact='Django')
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[<Post: First post>]
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>>> Post.objects.filter(tags__276='javascript')
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[]
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.. note::
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PostgreSQL uses 1-based indexing for array fields when writing raw SQL.
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However these indexes and those used in :lookup:`slices <arrayfield.slice>`
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use 0-based indexing to be consistent with Python.
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.. fieldlookup:: arrayfield.slice
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Slice transforms
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~~~~~~~~~~~~~~~~
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This class of transforms allow you to take a slice of the array. Any two
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non-negative integers can be used, separated by a single underscore. The
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lookups available after the transform do not change. For example::
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>>> Post.objects.create(name='First post', tags=['thoughts', 'django'])
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>>> Post.objects.create(name='Second post', tags=['thoughts'])
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>>> Post.objects.create(name='Third post', tags=['django', 'python', 'thoughts'])
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>>> Post.objects.filter(tags__0_1=['thoughts'])
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[<Post: First post>]
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>>> Post.objects.filter(tags__0_2__contains='thoughts')
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[<Post: First post>, <Post: Second post>]
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.. note::
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PostgreSQL uses 1-based indexing for array fields when writing raw SQL.
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However these slices and those used in :lookup:`indexes <arrayfield.index>`
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use 0-based indexing to be consistent with Python.
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.. admonition:: Multidimensional arrays with indexes and slices
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PostgreSQL has some rather esoteric behavior when using indexes and slices
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on multidimensional arrays. It will always work to use indexes to reach
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down to the final underlying data, but most other slices behave strangely
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at the database level and cannot be supported in a logical, consistent
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fashion by Django.
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Indexing ArrayField
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^^^^^^^^^^^^^^^^^^^
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At present using :attr:`~django.db.models.Field.db_index` will create a
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``btree`` index. This does not offer particularly significant help to querying.
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A more useful index is a ``GIN`` index, which you should create using a
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:class:`~django.db.migrations.operations.RunSQL` operation.
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HStoreField
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-----------
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.. class:: HStoreField(**options)
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A field for storing mappings of strings to strings. The Python data type
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used is a ``dict``.
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To use this field, you'll need to:
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1. Add ``'django.contrib.postgres'`` in your :setting:`INSTALLED_APPS`.
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2. Setup the hstore extension in PostgreSQL before the first ``CreateModel``
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or ``AddField`` operation by adding a migration with the
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:class:`~django.contrib.postgres.operations.HStoreExtension` operation.
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For example::
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from django.contrib.postgres.operations import HStoreExtension
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class Migration(migrations.Migration):
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...
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operations = [
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HStoreExtension(),
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...
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]
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Creating the extension requires a database user with superuser
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privileges. If the Django database user doesn't have superuser
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privileges, you'll have to create the extension outside of Django
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migrations with a user that has the appropriate privileges. In that
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case, connect to your Django database and run the query
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``CREATE EXTENSION IF NOT EXISTS hstore;``
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You'll see an error like ``can't adapt type 'dict'`` if you skip the first
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step, or ``type "hstore" does not exist`` if you skip the second.
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.. note::
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On occasions it may be useful to require or restrict the keys which are
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valid for a given field. This can be done using the
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:class:`~django.contrib.postgres.validators.KeysValidator`.
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Querying HStoreField
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^^^^^^^^^^^^^^^^^^^^
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In addition to the ability to query by key, there are a number of custom
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lookups available for ``HStoreField``.
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We will use the following example model::
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from django.contrib.postgres.fields import HStoreField
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from django.db import models
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class Dog(models.Model):
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name = models.CharField(max_length=200)
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data = HStoreField()
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def __str__(self): # __unicode__ on Python 2
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return self.name
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.. fieldlookup:: hstorefield.key
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Key lookups
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~~~~~~~~~~~
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To query based on a given key, you simply use that key as the lookup name::
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>>> Dog.objects.create(name='Rufus', data={'breed': 'labrador'})
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>>> Dog.objects.create(name='Meg', data={'breed': 'collie'})
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>>> Dog.objects.filter(data__breed='collie')
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[<Dog: Meg>]
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You can chain other lookups after key lookups::
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>>> Dog.objects.filter(data__breed__contains='l')
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[<Dog: Rufus>, <Dog: Meg>]
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If the key you wish to query by clashes with the name of another lookup, you
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need to use the :lookup:`hstorefield.contains` lookup instead.
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.. warning::
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Since any string could be a key in a hstore value, any lookup other than
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those listed below will be interpreted as a key lookup. No errors are
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raised. Be extra careful for typing mistakes, and always check your queries
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work as you intend.
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.. fieldlookup:: hstorefield.contains
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contains
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~~~~~~~~
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The :lookup:`contains` lookup is overridden on
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:class:`~django.contrib.postgres.fields.HStoreField`. The returned objects are
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those where the given ``dict`` of key-value pairs are all contained in the
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field. It uses the SQL operator ``@>``. For example::
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>>> Dog.objects.create(name='Rufus', data={'breed': 'labrador', 'owner': 'Bob'})
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>>> Dog.objects.create(name='Meg', data={'breed': 'collie', 'owner': 'Bob'})
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>>> Dog.objects.create(name='Fred', data={})
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>>> Dog.objects.filter(data__contains={'owner': 'Bob'})
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[<Dog: Rufus>, <Dog: Meg>]
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>>> Dog.objects.filter(data__contains={'breed': 'collie'})
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[<Dog: Meg>]
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.. fieldlookup:: hstorefield.contained_by
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contained_by
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~~~~~~~~~~~~
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This is the inverse of the :lookup:`contains <hstorefield.contains>` lookup -
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the objects returned will be those where the key-value pairs on the object are
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a subset of those in the value passed. It uses the SQL operator ``<@``. For
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example::
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>>> Dog.objects.create(name='Rufus', data={'breed': 'labrador', 'owner': 'Bob'})
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>>> Dog.objects.create(name='Meg', data={'breed': 'collie', 'owner': 'Bob'})
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>>> Dog.objects.create(name='Fred', data={})
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>>> Dog.objects.filter(data__contained_by={'breed': 'collie', 'owner': 'Bob'})
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[<Dog: Meg>, <Dog: Fred>]
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>>> Dog.objects.filter(data__contained_by={'breed': 'collie'})
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[<Dog: Fred>]
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.. fieldlookup:: hstorefield.has_key
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has_key
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~~~~~~~
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Returns objects where the given key is in the data. Uses the SQL operator
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``?``. For example::
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>>> Dog.objects.create(name='Rufus', data={'breed': 'labrador'})
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>>> Dog.objects.create(name='Meg', data={'breed': 'collie', 'owner': 'Bob'})
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>>> Dog.objects.filter(data__has_key='owner')
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[<Dog: Meg>]
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.. fieldlookup:: hstorefield.has_keys
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has_keys
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~~~~~~~~
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Returns objects where all of the given keys are in the data. Uses the SQL operator
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``?&``. For example::
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>>> Dog.objects.create(name='Rufus', data={})
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>>> Dog.objects.create(name='Meg', data={'breed': 'collie', 'owner': 'Bob'})
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>>> Dog.objects.filter(data__has_keys=['breed', 'owner'])
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[<Dog: Meg>]
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.. fieldlookup:: hstorefield.keys
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keys
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~~~~
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Returns objects where the array of keys is the given value. Note that the order
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is not guaranteed to be reliable, so this transform is mainly useful for using
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in conjunction with lookups on
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:class:`~django.contrib.postgres.fields.ArrayField`. Uses the SQL function
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``akeys()``. For example::
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>>> Dog.objects.create(name='Rufus', data={'toy': 'bone'})
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>>> Dog.objects.create(name='Meg', data={'breed': 'collie', 'owner': 'Bob'})
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>>> Dog.objects.filter(data__keys__overlap=['breed', 'toy'])
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[<Dog: Rufus>, <Dog: Meg>]
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.. fieldlookup:: hstorefield.values
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values
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~~~~~~
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Returns objects where the array of values is the given value. Note that the
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order is not guaranteed to be reliable, so this transform is mainly useful for
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using in conjunction with lookups on
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:class:`~django.contrib.postgres.fields.ArrayField`. Uses the SQL function
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``avalues()``. For example::
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>>> Dog.objects.create(name='Rufus', data={'breed': 'labrador'})
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>>> Dog.objects.create(name='Meg', data={'breed': 'collie', 'owner': 'Bob'})
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>>> Dog.objects.filter(data__values__contains=['collie'])
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[<Dog: Meg>]
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.. _range-fields:
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Range Fields
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------------
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There are five range field types, corresponding to the built-in range types in
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PostgreSQL. These fields are used to store a range of values; for example the
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start and end timestamps of an event, or the range of ages an activity is
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suitable for.
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All of the range fields translate to :ref:`psycopg2 Range objects
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<psycopg2:adapt-range>` in python, but also accept tuples as input if no bounds
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information is necessary. The default is lower bound included, upper bound
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excluded.
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IntegerRangeField
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^^^^^^^^^^^^^^^^^
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.. class:: IntegerRangeField(**options)
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Stores a range of integers. Based on an
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:class:`~django.db.models.IntegerField`. Represented by an ``int4range`` in
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the database and a :class:`~psycopg2:psycopg2.extras.NumericRange` in
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Python.
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BigIntegerRangeField
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^^^^^^^^^^^^^^^^^^^^
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.. class:: BigIntegerRangeField(**options)
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Stores a range of large integers. Based on a
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:class:`~django.db.models.BigIntegerField`. Represented by an ``int8range``
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in the database and a :class:`~psycopg2:psycopg2.extras.NumericRange` in
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Python.
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FloatRangeField
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^^^^^^^^^^^^^^^
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.. class:: FloatRangeField(**options)
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Stores a range of floating point values. Based on a
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:class:`~django.db.models.FloatField`. Represented by a ``numrange`` in the
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database and a :class:`~psycopg2:psycopg2.extras.NumericRange` in Python.
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DateTimeRangeField
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^^^^^^^^^^^^^^^^^^
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.. class:: DateTimeRangeField(**options)
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Stores a range of timestamps. Based on a
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:class:`~django.db.models.DateTimeField`. Represented by a ``tztsrange`` in
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the database and a :class:`~psycopg2:psycopg2.extras.DateTimeTZRange` in
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Python.
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DateRangeField
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^^^^^^^^^^^^^^
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.. class:: DateRangeField(**options)
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Stores a range of dates. Based on a
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:class:`~django.db.models.DateField`. Represented by a ``daterange`` in the
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database and a :class:`~psycopg2:psycopg2.extras.DateRange` in Python.
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Querying Range Fields
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^^^^^^^^^^^^^^^^^^^^^
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There are a number of custom lookups and transforms for range fields. They are
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available on all the above fields, but we will use the following example
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model::
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from django.contrib.postgres.fields import IntegerRangeField
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from django.db import models
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class Event(models.Model):
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name = models.CharField(max_length=200)
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ages = IntegerRangeField()
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def __str__(self): # __unicode__ on Python 2
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return self.name
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We will also use the following example objects::
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>>> Event.objects.create(name='Soft play', ages=(0, 10))
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>>> Event.objects.create(name='Pub trip', ages=(21, None))
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and ``NumericRange``:
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>>> from psycopg2.extras import NumericRange
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Containment functions
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~~~~~~~~~~~~~~~~~~~~~
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As with other PostgreSQL fields, there are three standard containment
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operators: ``contains``, ``contained_by`` and ``overlap``, using the SQL
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operators ``@>``, ``<@``, and ``&&`` respectively.
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.. fieldlookup:: rangefield.contains
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contains
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''''''''
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>>> Event.objects.filter(ages__contains=NumericRange(4, 5))
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[<Event: Soft play>]
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.. fieldlookup:: rangefield.contained_by
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contained_by
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''''''''''''
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>>> Event.objects.filter(ages__contained_by=NumericRange(0, 15))
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[<Event: Soft play>]
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.. fieldlookup:: rangefield.overlap
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overlap
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'''''''
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>>> Event.objects.filter(ages__overlap=NumericRange(8, 12))
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[<Event: Soft play>]
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Comparison functions
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~~~~~~~~~~~~~~~~~~~~
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Range fields support the standard lookups: :lookup:`lt`, :lookup:`gt`,
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:lookup:`lte` and :lookup:`gte`. These are not particularly helpful - they
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compare the lower bounds first and then the upper bounds only if necessary.
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This is also the strategy used to order by a range field. It is better to use
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the specific range comparison operators.
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.. fieldlookup:: rangefield.fully_lt
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fully_lt
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''''''''
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The returned ranges are strictly less than the passed range. In other words,
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all the points in the returned range are less than all those in the passed
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range.
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>>> Event.objects.filter(ages__fully_lt=NumericRange(11, 15))
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[<Event: Soft play>]
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.. fieldlookup:: rangefield.fully_gt
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fully_gt
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''''''''
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The returned ranges are strictly greater than the passed range. In other words,
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the all the points in the returned range are greater than all those in the
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passed range.
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>>> Event.objects.filter(ages__fully_gt=NumericRange(11, 15))
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[<Event: Pub trip>]
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.. fieldlookup:: rangefield.not_lt
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not_lt
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''''''
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The returned ranges do not contain any points less than the passed range, that
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is the lower bound of the returned range is at least the lower bound of the
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passed range.
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>>> Event.objects.filter(ages__not_lt=NumericRange(0, 15))
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[<Event: Soft play>, <Event: Pub trip>]
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.. fieldlookup:: rangefield.not_gt
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not_gt
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''''''
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The returned ranges do not contain any points greater than the passed range, that
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is the upper bound of the returned range is at most the upper bound of the
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passed range.
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>>> Event.objects.filter(ages__not_gt=NumericRange(3, 10))
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[<Event: Soft play>]
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.. fieldlookup:: rangefield.adjacent_to
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adjacent_to
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'''''''''''
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The returned ranges share a bound with the passed range.
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>>> Event.objects.filter(ages__adjacent_to=NumericRange(10, 21))
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[<Event: Soft play>, <Event: Pub trip>]
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Querying using the bounds
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~~~~~~~~~~~~~~~~~~~~~~~~~
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There are three transforms available for use in queries. You can extract the
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lower or upper bound, or query based on emptiness.
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.. fieldlookup:: rangefield.startswith
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startswith
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''''''''''
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Returned objects have the given lower bound. Can be chained to valid lookups
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for the base field.
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>>> Event.objects.filter(ages__startswith=21)
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[<Event: Pub trip>]
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.. fieldlookup:: rangefield.endswith
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endswith
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''''''''
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Returned objects have the given upper bound. Can be chained to valid lookups
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for the base field.
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>>> Event.objects.filter(ages__endswith=10)
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[<Event: Soft play>]
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.. fieldlookup:: rangefield.isempty
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isempty
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'''''''
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Returned objects are empty ranges. Can be chained to valid lookups for a
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:class:`~django.db.models.BooleanField`.
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>>> Event.objects.filter(ages__isempty=True)
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[]
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Defining your own range types
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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PostgreSQL allows the definition of custom range types. Django's model and form
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field implementations use base classes below, and psycopg2 provides a
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:func:`~psycopg2:psycopg2.extras.register_range` to allow use of custom range
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types.
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.. class:: RangeField(**options)
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Base class for model range fields.
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.. attribute:: base_field
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The model field to use.
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.. attribute:: range_type
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The psycopg2 range type to use.
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.. attribute:: form_field
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The form field class to use. Should be a subclass of
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:class:`django.contrib.postgres.forms.BaseRangeField`.
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.. class:: django.contrib.postgres.forms.BaseRangeField
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Base class for form range fields.
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.. attribute:: base_field
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The form field to use.
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.. attribute:: range_type
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The psycopg2 range type to use.
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