File: fields.rst

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.. _ref-fields:

===============
Resource Fields
===============

When designing an API, an important component is defining the representation
of the data you're presenting. Like Django models, you can control the
representation of a ``Resource`` using fields. There are a variety of fields
for various types of data.


Quick Start
===========

For the impatient::

  import datetime
  from tastypie import fields
  from tastypie.resources import Resource
  from myapp.api.resources import ProfileResource, NoteResource
  
  
  class PersonResource(Resource):
      name = fields.CharField(attribute='name')
      age = fields.IntegerField(attribute='years_old', null=True)
      created = fields.DateTimeField(readonly=True, help_text='When the person was created', default=datetime.datetime.now)
      is_active = fields.BooleanField(default=True)
      profile = fields.ToOneField(ProfileResource, 'profile')
      notes = fields.ToManyField(NoteResource, 'notes', full=True)


Standard Data Fields
====================

All standard data fields have a common base class ``ApiField`` which handles
the basic implementation details.

.. note::

  You should not use the ``ApiField`` class directly. Please use one of the
  subclasses that is more correct for your data.

Common Field Options
--------------------

All ``ApiField`` objects accept the following options.

``attribute``
~~~~~~~~~~~~~

.. attribute:: ApiField.attribute

A string naming an instance attribute of the object wrapped by the Resource. The
attribute will be accessed during the ``dehydrate`` or or written during the ``hydrate``.

Defaults to ``None``, meaning data will be manually accessed.

``default``
~~~~~~~~~~~

.. attribute:: ApiField.default

Provides default data when the object being ``dehydrated``/``hydrated`` has no data on
the field.

Defaults to ``tastypie.fields.NOT_PROVIDED``.

``null``
~~~~~~~~

.. attribute:: ApiField.null

Indicates whether or not a ``None`` is allowable data on the field. Defaults to
``False``.

``readonly``
~~~~~~~~~~~~

.. attribute:: ApiField.readonly

Indicates whether the field is used during the ``hydrate`` or not. Defaults to ``False``.

``unique``
~~~~~~~~~~

.. attribute:: ApiField.unique

Indicates whether the field is a unique identifier for the object.

``help_text``
~~~~~~~~~~~~~

.. attribute:: ApiField.help_text

A human-readable description of the field exposed at the schema level.
Defaults to the per-Field definition.


Field Types
-----------

.. module:: tastypie.fields

``BooleanField``
----------------

A boolean field.

Covers both ``models.BooleanField`` and ``models.NullBooleanField``.

``CharField``
-------------

A text field of arbitrary length.

Covers both ``models.CharField`` and ``models.TextField``.

``DateField``
-------------

A date field.

``DateTimeField``
-----------------

A datetime field.

``DecimalField``
----------------

A decimal field.

``DictField``
-------------

A dictionary field.

``FileField``
-------------

A file-related field.

Covers both ``models.FileField`` and ``models.ImageField``.

``FloatField``
--------------

A floating point field.

``IntegerField``
----------------

An integer field.

Covers ``models.IntegerField``, ``models.PositiveIntegerField``,
``models.PositiveSmallIntegerField`` and ``models.SmallIntegerField``.

``ListField``
-------------

A list field.


Relationship Fields
===================

Provides access to data that is related within the database.

The ``RelatedField`` base class is not intended for direct use but provides
functionality that ``ToOneField`` and ``ToManyField`` build upon.

The contents of this field actually point to another ``Resource``,
rather than the related object. This allows the field to represent its data
in different ways.

The abstractions based around this are "leaky" in that, unlike the other
fields provided by ``tastypie``, these fields don't handle arbitrary objects
very well. The subclasses use Django's ORM layer to make things go, though
there is no ORM-specific code at this level.

Common Field Options
--------------------

In addition to the common attributes for all `ApiField`, relationship fields
accept the following.

``to``
~~~~~~

.. attribute:: RelatedField.to

The ``to`` argument should point to a ``Resource`` class, NOT to a ``Model``.
Required.

``full``
~~~~~~~~

.. attribute:: RelatedField.full

Indicates how the related ``Resource`` will appear post-``dehydrate``. If
``False``, the related ``Resource`` will appear as a URL to the endpoint of
that resource. If ``True``, the result of the sub-resource's ``dehydrate`` will
be included in full.

``related_name``
~~~~~~~~~~~~~~~~

.. attribute:: RelatedField.related_name

Currently unused, as unlike Django's ORM layer, reverse relations between
``Resource`` classes are not automatically created. Defaults to ``None``.


Field Types
-----------

``ToOneField``
~~~~~~~~~~~~~~

Provides access to related data via foreign key.

This subclass requires Django's ORM layer to work properly.

``OneToOneField``
~~~~~~~~~~~~~~~~~

An alias to ``ToOneField`` for those who prefer to mirror ``django.db.models``.

``ForeignKey``
~~~~~~~~~~~~~~

An alias to ``ToOneField`` for those who prefer to mirror ``django.db.models``.

``ToManyField``
~~~~~~~~~~~~~~~

Provides access to related data via a join table.

This subclass requires Django's ORM layer to work properly.

This field also has special behavior when dealing with ``attribute`` in that
it can take a callable. For instance, if you need to filter the reverse
relation, you can do something like::

    subjects = fields.ToManyField(SubjectResource, ToManyField(SubjectResource, attribute=lambda bundle: Subject.objects.filter(notes=bundle.obj, name__startswith='Personal'))

Note that the ``hydrate`` portions of this field are quite different than
any other field. ``hydrate_m2m`` actually handles the data and relations.
This is due to the way Django implements M2M relationships.

``ManyToManyField``
~~~~~~~~~~~~~~~~~~~

An alias to ``ToManyField`` for those who prefer to mirror ``django.db.models``.

``OneToManyField``
~~~~~~~~~~~~~~~~~~

An alias to ``ToManyField`` for those who prefer to mirror ``django.db.models``.