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Diffstat (limited to 'docs/api-guide/relations.md')
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diff --git a/docs/api-guide/relations.md b/docs/api-guide/relations.md index 50c9bc54..093bbdd0 100644 --- a/docs/api-guide/relations.md +++ b/docs/api-guide/relations.md @@ -1,4 +1,4 @@ -<a class="github" href="relations.py"></a> +source: relations.py # Serializer relations @@ -16,6 +16,20 @@ Relational fields are used to represent model relationships. They can be applie --- +#### Inspecting automatically generated relationships. + +When using the `ModelSerializer` class, serializer fields and relationships will be automatically generated for you. Inspecting these automatically generated fields can be a useful tool for determining how to customize the relationship style. + +To do so, open the Django shell, using `python manage.py shell`, then import the serializer class, instantiate it, and print the object representation… + + >>> from myapp.serializers import AccountSerializer + >>> serializer = AccountSerializer() + >>> print repr(serializer) # Or `print(repr(serializer))` in Python 3.x. + AccountSerializer(): + id = IntegerField(label='ID', read_only=True) + name = CharField(allow_blank=True, max_length=100, required=False) + owner = PrimaryKeyRelatedField(queryset=User.objects.all()) + # API Reference In order to explain the various types of relational fields, we'll use a couple of simple models for our examples. Our models will be for music albums, and the tracks listed on each album. @@ -33,19 +47,19 @@ In order to explain the various types of relational fields, we'll use a couple o class Meta: unique_together = ('album', 'order') order_by = 'order' - + def __unicode__(self): return '%d: %s' % (self.order, self.title) -## RelatedField +## StringRelatedField -`RelatedField` may be used to represent the target of the relationship using it's `__unicode__` method. +`StringRelatedField` may be used to represent the target of the relationship using its `__unicode__` method. For example, the following serializer. - + class AlbumSerializer(serializers.ModelSerializer): - tracks = RelatedField(many=True) - + tracks = serializers.StringRelatedField(many=True) + class Meta: model = Album fields = ('album_name', 'artist', 'tracks') @@ -54,7 +68,7 @@ Would serialize to the following representation. { 'album_name': 'Things We Lost In The Fire', - 'artist': 'Low' + 'artist': 'Low', 'tracks': [ '1: Sunflower', '2: Whitetail', @@ -71,13 +85,13 @@ This field is read only. ## PrimaryKeyRelatedField -`PrimaryKeyRelatedField` may be used to represent the target of the relationship using it's primary key. +`PrimaryKeyRelatedField` may be used to represent the target of the relationship using its primary key. For example, the following serializer: - + class AlbumSerializer(serializers.ModelSerializer): - tracks = PrimaryKeyRelatedField(many=True, read_only=True) - + tracks = serializers.PrimaryKeyRelatedField(many=True, read_only=True) + class Meta: model = Album fields = ('album_name', 'artist', 'tracks') @@ -86,7 +100,7 @@ Would serialize to a representation like this: { 'album_name': 'The Roots', - 'artist': 'Undun' + 'artist': 'Undun', 'tracks': [ 89, 90, @@ -99,20 +113,23 @@ By default this field is read-write, although you can change this behavior using **Arguments**: +* `queryset` - The queryset used for model instance lookups when validating the field input. Relationships must either set a queryset explicitly, or set `read_only=True`. * `many` - If applied to a to-many relationship, you should set this argument to `True`. -* `required` - If set to `False`, the field will accept values of `None` or the empty-string for nullable relationships. -* `queryset` - By default `ModelSerializer` classes will use the default queryset for the relationship. `Serializer` classes must either set a queryset explicitly, or set `read_only=True`. +* `allow_null` - If set to `True`, the field will accept values of `None` or the empty string for nullable relationships. Defaults to `False`. ## HyperlinkedRelatedField `HyperlinkedRelatedField` may be used to represent the target of the relationship using a hyperlink. For example, the following serializer: - + class AlbumSerializer(serializers.ModelSerializer): - tracks = HyperlinkedRelatedField(many=True, read_only=True, - view_name='track-detail') - + tracks = serializers.HyperlinkedRelatedField( + many=True, + read_only=True, + view_name='track-detail' + ) + class Meta: model = Album fields = ('album_name', 'artist', 'tracks') @@ -121,7 +138,7 @@ Would serialize to a representation like this: { 'album_name': 'Graceland', - 'artist': 'Paul Simon' + 'artist': 'Paul Simon', 'tracks': [ 'http://www.example.com/api/tracks/45/', 'http://www.example.com/api/tracks/46/', @@ -134,11 +151,12 @@ By default this field is read-write, although you can change this behavior using **Arguments**: -* `view_name` - The view name that should be used as the target of the relationship. **required**. +* `view_name` - The view name that should be used as the target of the relationship. If you're using [the standard router classes][routers] this will be a string with the format `<modelname>-detail`. **required**. +* `queryset` - The queryset used for model instance lookups when validating the field input. Relationships must either set a queryset explicitly, or set `read_only=True`. * `many` - If applied to a to-many relationship, you should set this argument to `True`. -* `required` - If set to `False`, the field will accept values of `None` or the empty-string for nullable relationships. -* `queryset` - By default `ModelSerializer` classes will use the default queryset for the relationship. `Serializer` classes must either set a queryset explicitly, or set `read_only=True`. +* `allow_null` - If set to `True`, the field will accept values of `None` or the empty string for nullable relationships. Defaults to `False`. * `lookup_field` - The field on the target that should be used for the lookup. Should correspond to a URL keyword argument on the referenced view. Default is `'pk'`. +* `lookup_url_kwarg` - The name of the keyword argument defined in the URL conf that corresponds to the lookup field. Defaults to using the same value as `lookup_field`. * `format` - If using format suffixes, hyperlinked fields will use the same format suffix for the target unless overridden by using the `format` argument. ## SlugRelatedField @@ -146,10 +164,14 @@ By default this field is read-write, although you can change this behavior using `SlugRelatedField` may be used to represent the target of the relationship using a field on the target. For example, the following serializer: - + class AlbumSerializer(serializers.ModelSerializer): - tracks = SlugRelatedField(many=True, read_only=True, slug_field='title') - + tracks = serializers.SlugRelatedField( + many=True, + read_only=True, + slug_field='title' + ) + class Meta: model = Album fields = ('album_name', 'artist', 'tracks') @@ -158,7 +180,7 @@ Would serialize to a representation like this: { 'album_name': 'Dear John', - 'artist': 'Loney Dear' + 'artist': 'Loney Dear', 'tracks': [ 'Airport Surroundings', 'Everything Turns to You', @@ -174,16 +196,16 @@ When using `SlugRelatedField` as a read-write field, you will normally want to e **Arguments**: * `slug_field` - The field on the target that should be used to represent it. This should be a field that uniquely identifies any given instance. For example, `username`. **required** +* `queryset` - The queryset used for model instance lookups when validating the field input. Relationships must either set a queryset explicitly, or set `read_only=True`. * `many` - If applied to a to-many relationship, you should set this argument to `True`. -* `required` - If set to `False`, the field will accept values of `None` or the empty-string for nullable relationships. -* `queryset` - By default `ModelSerializer` classes will use the default queryset for the relationship. `Serializer` classes must either set a queryset explicitly, or set `read_only=True`. +* `allow_null` - If set to `True`, the field will accept values of `None` or the empty string for nullable relationships. Defaults to `False`. ## HyperlinkedIdentityField This field can be applied as an identity relationship, such as the `'url'` field on a HyperlinkedModelSerializer. It can also be used for an attribute on the object. For example, the following serializer: class AlbumSerializer(serializers.HyperlinkedModelSerializer): - track_listing = HyperlinkedIdentityField(view_name='track-list') + track_listing = serializers.HyperlinkedIdentityField(view_name='track-list') class Meta: model = Album @@ -193,7 +215,7 @@ Would serialize to a representation like this: { 'album_name': 'The Eraser', - 'artist': 'Thom Yorke' + 'artist': 'Thom Yorke', 'track_listing': 'http://www.example.com/api/track_list/12/', } @@ -201,8 +223,9 @@ This field is always read-only. **Arguments**: -* `view_name` - The view name that should be used as the target of the relationship. **required**. +* `view_name` - The view name that should be used as the target of the relationship. If you're using [the standard router classes][routers] this will be a string with the format `<model_name>-detail`. **required**. * `lookup_field` - The field on the target that should be used for the lookup. Should correspond to a URL keyword argument on the referenced view. Default is `'pk'`. +* `lookup_url_kwarg` - The name of the keyword argument defined in the URL conf that corresponds to the lookup field. Defaults to using the same value as `lookup_field`. * `format` - If using format suffixes, hyperlinked fields will use the same format suffix for the target unless overridden by using the `format` argument. --- @@ -213,8 +236,6 @@ Nested relationships can be expressed by using serializers as fields. If the field is used to represent a to-many relationship, you should add the `many=True` flag to the serializer field. -Note that nested relationships are currently read-only. For read-write relationships, you should use a flat relational style. - ## Example For example, the following serializer: @@ -223,10 +244,10 @@ For example, the following serializer: class Meta: model = Track fields = ('order', 'title') - + class AlbumSerializer(serializers.ModelSerializer): - tracks = TrackSerializer(many=True) - + tracks = TrackSerializer(many=True, read_only=True) + class Meta: model = Album fields = ('album_name', 'artist', 'tracks') @@ -235,7 +256,7 @@ Would serialize to a nested representation like this: { 'album_name': 'The Grey Album', - 'artist': 'Danger Mouse' + 'artist': 'Danger Mouse', 'tracks': [ {'order': 1, 'title': 'Public Service Announcement'}, {'order': 2, 'title': 'What More Can I Say'}, @@ -246,24 +267,24 @@ Would serialize to a nested representation like this: # Custom relational fields -To implement a custom relational field, you should override `RelatedField`, and implement the `.to_native(self, value)` method. This method takes the target of the field as the `value` argument, and should return the representation that should be used to serialize the target. +To implement a custom relational field, you should override `RelatedField`, and implement the `.to_representation(self, value)` method. This method takes the target of the field as the `value` argument, and should return the representation that should be used to serialize the target. The `value` argument will typically be a model instance. -If you want to implement a read-write relational field, you must also implement the `.from_native(self, data)` method, and add `read_only = False` to the class definition. +If you want to implement a read-write relational field, you must also implement the `.to_internal_value(self, data)` method. ## Example -For, example, we could define a relational field, to serialize a track to a custom string representation, using it's ordering, title, and duration. +For, example, we could define a relational field, to serialize a track to a custom string representation, using its ordering, title, and duration. import time class TrackListingField(serializers.RelatedField): - def to_native(self, value): + def to_representation(self, value): duration = time.strftime('%M:%S', time.gmtime(value.duration)) return 'Track %d: %s (%s)' % (value.order, value.name, duration) class AlbumSerializer(serializers.ModelSerializer): tracks = TrackListingField(many=True) - + class Meta: model = Album fields = ('album_name', 'artist', 'tracks') @@ -272,7 +293,7 @@ This custom field would then serialize to the following representation. { 'album_name': 'Sometimes I Wish We Were an Eagle', - 'artist': 'Bill Callahan' + 'artist': 'Bill Callahan', 'tracks': [ 'Track 1: Jim Cain (04:39)', 'Track 2: Eid Ma Clack Shaw (04:19)', @@ -285,6 +306,16 @@ This custom field would then serialize to the following representation. # Further notes +## The `queryset` argument + +The `queryset` argument is only ever required for *writable* relationship field, in which case it is used for performing the model instance lookup, that maps from the primitive user input, into a model instance. + +In version 2.x a serializer class could *sometimes* automatically determine the `queryset` argument *if* a `ModelSerializer` class was being used. + +This behavior is now replaced with *always* using an explicit `queryset` argument for writable relational fields. + +Doing so reduces the amount of hidden 'magic' that `ModelSerializer` provides, makes the behavior of the field more clear, and ensures that it is trivial to move between using the `ModelSerializer` shortcut, or using fully explicit `Serializer` classes. + ## Reverse relations Note that reverse relationships are not automatically included by the `ModelSerializer` and `HyperlinkedModelSerializer` classes. To include a reverse relationship, you must explicitly add it to the fields list. For example: @@ -303,7 +334,7 @@ If you have not set a related name for the reverse relationship, you'll need to class AlbumSerializer(serializers.ModelSerializer): class Meta: - fields = ('track_set', ...) + fields = ('track_set', ...) See the Django documentation on [reverse relationships][reverse-relationships] for more details. @@ -316,14 +347,14 @@ For example, given the following model for a tag, which has a generic relationsh class TaggedItem(models.Model): """ Tags arbitrary model instances using a generic relation. - + See: https://docs.djangoproject.com/en/dev/ref/contrib/contenttypes/ """ tag_name = models.SlugField() content_type = models.ForeignKey(ContentType) object_id = models.PositiveIntegerField() tagged_object = GenericForeignKey('content_type', 'object_id') - + def __unicode__(self): return self.tag @@ -351,23 +382,23 @@ We could define a custom field that could be used to serialize tagged instances, A custom field to use for the `tagged_object` generic relationship. """ - def to_native(self, value): + def to_representation(self, value): """ Serialize tagged objects to a simple textual representation. - """ + """ if isinstance(value, Bookmark): return 'Bookmark: ' + value.url elif isinstance(value, Note): return 'Note: ' + value.text raise Exception('Unexpected type of tagged object') -If you need the target of the relationship to have a nested representation, you can use the required serializers inside the `.to_native()` method: +If you need the target of the relationship to have a nested representation, you can use the required serializers inside the `.to_representation()` method: - def to_native(self, value): + def to_representation(self, value): """ Serialize bookmark instances using a bookmark serializer, and note instances using a note serializer. - """ + """ if isinstance(value, Bookmark): serializer = BookmarkSerializer(value) elif isinstance(value, Note): @@ -386,13 +417,13 @@ For more information see [the Django documentation on generic relations][generic By default, relational fields that target a ``ManyToManyField`` with a ``through`` model specified are set to read-only. -If you exlicitly specify a relational field pointing to a +If you explicitly specify a relational field pointing to a ``ManyToManyField`` with a through model, be sure to set ``read_only`` to ``True``. ## Advanced Hyperlinked fields -If you have very specific requirements for the style of your hyperlinked relationships you can override `HyperlinkedRelatedField`. +If you have very specific requirements for the style of your hyperlinked relationships you can override `HyperlinkedRelatedField`. There are two methods you'll need to override. @@ -405,14 +436,13 @@ attributes are not configured to correctly match the URL conf. #### get_object(self, queryset, view_name, view_args, view_kwargs) - This method should the object that corresponds to the matched URL conf arguments. May raise an `ObjectDoesNotExist` exception. ### Example -For example, if all your object URLs used both a account and a slug in the the URL to reference the object, you might create a custom field like this: +For example, if all your object URLs used both a account and a slug in the the URL to reference the object, you might create a custom field like this: class CustomHyperlinkedField(serializers.HyperlinkedRelatedField): def get_url(self, obj, view_name, request, format): @@ -422,28 +452,21 @@ For example, if all your object URLs used both a account and a slug in the the U def get_object(self, queryset, view_name, view_args, view_kwargs): account = view_kwargs['account'] slug = view_kwargs['slug'] - return queryset.get(account=account, slug=sug) + return queryset.get(account=account, slug=slug) --- -## Deprecated APIs - -The following classes have been deprecated, in favor of the `many=<bool>` syntax. -They continue to function, but their usage will raise a `PendingDeprecationWarning`, which is silent by default. - -* `ManyRelatedField` -* `ManyPrimaryKeyRelatedField` -* `ManyHyperlinkedRelatedField` -* `ManySlugRelatedField` +# Third Party Packages -The `null=<bool>` flag has been deprecated in favor of the `required=<bool>` flag. It will continue to function, but will raise a `PendingDeprecationWarning`. +The following third party packages are also available. -In the 2.3 release, these warnings will be escalated to a `DeprecationWarning`, which is loud by default. -In the 2.4 release, these parts of the API will be removed entirely. +## DRF Nested Routers -For more details see the [2.2 release announcement][2.2-announcement]. +The [drf-nested-routers package][drf-nested-routers] provides routers and relationship fields for working with nested resources. [cite]: http://lwn.net/Articles/193245/ [reverse-relationships]: https://docs.djangoproject.com/en/dev/topics/db/queries/#following-relationships-backward +[routers]: http://www.django-rest-framework.org/api-guide/routers#defaultrouter [generic-relations]: https://docs.djangoproject.com/en/dev/ref/contrib/contenttypes/#id1 [2.2-announcement]: ../topics/2.2-announcement.md +[drf-nested-routers]: https://github.com/alanjds/drf-nested-routers |