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They can be applied to <code>ForeignKey</code>, <code>ManyToManyField</code> and <code>OneToOneField</code> relationships, as well as to reverse relationships, and custom relationships such as <code>GenericForeignKey</code>.</p> +<hr /> +<p><strong>Note:</strong> The relational fields are declared in <code>relations.py</code>, but by convention you should import them from the <code>serializers</code> module, using <code>from rest_framework import serializers</code> and refer to fields as <code>serializers.<FieldName></code>.</p> +<hr /> +<h1 id="api-reference">API Reference</h1> +<p>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.</p> +<pre class="prettyprint lang-py"><code>class Album(models.Model): + album_name = models.CharField(max_length=100) + artist = models.CharField(max_length=100) + +class Track(models.Model): + album = models.ForeignKey(Album, related_name='tracks') + order = models.IntegerField() + title = models.CharField(max_length=100) + duration = models.IntegerField() + + class Meta: + unique_together = ('album', 'order') + order_by = 'order' + + def __unicode__(self): + return '%d: %s' % (self.order, self.title) +</code></pre> +<h2 id="relatedfield">RelatedField</h2> +<p><code>RelatedField</code> may be used to represent the target of the relationship using its <code>__unicode__</code> method.</p> +<p>For example, the following serializer.</p> +<pre class="prettyprint lang-py"><code>class AlbumSerializer(serializers.ModelSerializer): + tracks = RelatedField(many=True) + + class Meta: + model = Album + fields = ('album_name', 'artist', 'tracks') +</code></pre> +<p>Would serialize to the following representation.</p> +<pre class="prettyprint lang-py"><code>{ + 'album_name': 'Things We Lost In The Fire', + 'artist': 'Low', + 'tracks': [ + '1: Sunflower', + '2: Whitetail', + '3: Dinosaur Act', + ... + ] +} +</code></pre> +<p>This field is read only.</p> +<p><strong>Arguments</strong>:</p> +<ul> +<li><code>many</code> - If applied to a to-many relationship, you should set this argument to <code>True</code>.</li> +</ul> +<h2 id="primarykeyrelatedfield">PrimaryKeyRelatedField</h2> +<p><code>PrimaryKeyRelatedField</code> may be used to represent the target of the relationship using its primary key.</p> +<p>For example, the following serializer:</p> +<pre class="prettyprint lang-py"><code>class AlbumSerializer(serializers.ModelSerializer): + tracks = serializers.PrimaryKeyRelatedField(many=True, read_only=True) + + class Meta: + model = Album + fields = ('album_name', 'artist', 'tracks') +</code></pre> +<p>Would serialize to a representation like this:</p> +<pre class="prettyprint lang-py"><code>{ + 'album_name': 'The Roots', + 'artist': 'Undun', + 'tracks': [ + 89, + 90, + 91, + ... + ] +} +</code></pre> +<p>By default this field is read-write, although you can change this behavior using the <code>read_only</code> flag.</p> +<p><strong>Arguments</strong>:</p> +<ul> +<li><code>many</code> - If applied to a to-many relationship, you should set this argument to <code>True</code>.</li> +<li><code>required</code> - If set to <code>False</code>, the field will accept values of <code>None</code> or the empty-string for nullable relationships.</li> +<li><code>queryset</code> - By default <code>ModelSerializer</code> classes will use the default queryset for the relationship. <code>Serializer</code> classes must either set a queryset explicitly, or set <code>read_only=True</code>.</li> +</ul> +<h2 id="hyperlinkedrelatedfield">HyperlinkedRelatedField</h2> +<p><code>HyperlinkedRelatedField</code> may be used to represent the target of the relationship using a hyperlink.</p> +<p>For example, the following serializer:</p> +<pre class="prettyprint lang-py"><code>class AlbumSerializer(serializers.ModelSerializer): + tracks = serializers.HyperlinkedRelatedField(many=True, read_only=True, + view_name='track-detail') + + class Meta: + model = Album + fields = ('album_name', 'artist', 'tracks') +</code></pre> +<p>Would serialize to a representation like this:</p> +<pre class="prettyprint lang-py"><code>{ + 'album_name': 'Graceland', + 'artist': 'Paul Simon', + 'tracks': [ + 'http://www.example.com/api/tracks/45/', + 'http://www.example.com/api/tracks/46/', + 'http://www.example.com/api/tracks/47/', + ... + ] +} +</code></pre> +<p>By default this field is read-write, although you can change this behavior using the <code>read_only</code> flag.</p> +<p><strong>Arguments</strong>:</p> +<ul> +<li><code>view_name</code> - The view name that should be used as the target of the relationship. <strong>required</strong>.</li> +<li><code>many</code> - If applied to a to-many relationship, you should set this argument to <code>True</code>.</li> +<li><code>required</code> - If set to <code>False</code>, the field will accept values of <code>None</code> or the empty-string for nullable relationships.</li> +<li><code>queryset</code> - By default <code>ModelSerializer</code> classes will use the default queryset for the relationship. <code>Serializer</code> classes must either set a queryset explicitly, or set <code>read_only=True</code>.</li> +<li><code>lookup_field</code> - 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 <code>'pk'</code>.</li> +<li><code>format</code> - If using format suffixes, hyperlinked fields will use the same format suffix for the target unless overridden by using the <code>format</code> argument.</li> +</ul> +<h2 id="slugrelatedfield">SlugRelatedField</h2> +<p><code>SlugRelatedField</code> may be used to represent the target of the relationship using a field on the target.</p> +<p>For example, the following serializer:</p> +<pre class="prettyprint lang-py"><code>class AlbumSerializer(serializers.ModelSerializer): + tracks = serializers.SlugRelatedField(many=True, read_only=True, + slug_field='title') + + class Meta: + model = Album + fields = ('album_name', 'artist', 'tracks') +</code></pre> +<p>Would serialize to a representation like this:</p> +<pre class="prettyprint lang-py"><code>{ + 'album_name': 'Dear John', + 'artist': 'Loney Dear', + 'tracks': [ + 'Airport Surroundings', + 'Everything Turns to You', + 'I Was Only Going Out', + ... + ] +} +</code></pre> +<p>By default this field is read-write, although you can change this behavior using the <code>read_only</code> flag.</p> +<p>When using <code>SlugRelatedField</code> as a read-write field, you will normally want to ensure that the slug field corresponds to a model field with <code>unique=True</code>.</p> +<p><strong>Arguments</strong>:</p> +<ul> +<li><code>slug_field</code> - 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, <code>username</code>. <strong>required</strong></li> +<li><code>many</code> - If applied to a to-many relationship, you should set this argument to <code>True</code>.</li> +<li><code>required</code> - If set to <code>False</code>, the field will accept values of <code>None</code> or the empty-string for nullable relationships.</li> +<li><code>queryset</code> - By default <code>ModelSerializer</code> classes will use the default queryset for the relationship. <code>Serializer</code> classes must either set a queryset explicitly, or set <code>read_only=True</code>.</li> +</ul> +<h2 id="hyperlinkedidentityfield">HyperlinkedIdentityField</h2> +<p>This field can be applied as an identity relationship, such as the <code>'url'</code> field on a HyperlinkedModelSerializer. It can also be used for an attribute on the object. For example, the following serializer:</p> +<pre class="prettyprint lang-py"><code>class AlbumSerializer(serializers.HyperlinkedModelSerializer): + track_listing = serializers.HyperlinkedIdentityField(view_name='track-list') + + class Meta: + model = Album + fields = ('album_name', 'artist', 'track_listing') +</code></pre> +<p>Would serialize to a representation like this:</p> +<pre class="prettyprint lang-py"><code>{ + 'album_name': 'The Eraser', + 'artist': 'Thom Yorke', + 'track_listing': 'http://www.example.com/api/track_list/12/', +} +</code></pre> +<p>This field is always read-only.</p> +<p><strong>Arguments</strong>:</p> +<ul> +<li><code>view_name</code> - The view name that should be used as the target of the relationship. <strong>required</strong>.</li> +<li><code>lookup_field</code> - 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 <code>'pk'</code>.</li> +<li><code>format</code> - If using format suffixes, hyperlinked fields will use the same format suffix for the target unless overridden by using the <code>format</code> argument.</li> +</ul> +<hr /> +<h1 id="nested-relationships">Nested relationships</h1> +<p>Nested relationships can be expressed by using serializers as fields.</p> +<p>If the field is used to represent a to-many relationship, you should add the <code>many=True</code> flag to the serializer field.</p> +<h2 id="example">Example</h2> +<p>For example, the following serializer:</p> +<pre class="prettyprint lang-py"><code>class TrackSerializer(serializers.ModelSerializer): + class Meta: + model = Track + fields = ('order', 'title') + +class AlbumSerializer(serializers.ModelSerializer): + tracks = TrackSerializer(many=True) + + class Meta: + model = Album + fields = ('album_name', 'artist', 'tracks') +</code></pre> +<p>Would serialize to a nested representation like this:</p> +<pre class="prettyprint lang-py"><code>{ + 'album_name': 'The Grey Album', + 'artist': 'Danger Mouse', + 'tracks': [ + {'order': 1, 'title': 'Public Service Announcement'}, + {'order': 2, 'title': 'What More Can I Say'}, + {'order': 3, 'title': 'Encore'}, + ... + ], +} +</code></pre> +<h1 id="custom-relational-fields">Custom relational fields</h1> +<p>To implement a custom relational field, you should override <code>RelatedField</code>, and implement the <code>.to_native(self, value)</code> method. This method takes the target of the field as the <code>value</code> argument, and should return the representation that should be used to serialize the target.</p> +<p>If you want to implement a read-write relational field, you must also implement the <code>.from_native(self, data)</code> method, and add <code>read_only = False</code> to the class definition.</p> +<h2 id="example_1">Example</h2> +<p>For, example, we could define a relational field, to serialize a track to a custom string representation, using its ordering, title, and duration.</p> +<pre class="prettyprint lang-py"><code>import time + +class TrackListingField(serializers.RelatedField): + def to_native(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') +</code></pre> +<p>This custom field would then serialize to the following representation.</p> +<pre class="prettyprint lang-py"><code>{ + 'album_name': 'Sometimes I Wish We Were an Eagle', + 'artist': 'Bill Callahan', + 'tracks': [ + 'Track 1: Jim Cain (04:39)', + 'Track 2: Eid Ma Clack Shaw (04:19)', + 'Track 3: The Wind and the Dove (04:34)', + ... + ] +} +</code></pre> +<hr /> +<h1 id="further-notes">Further notes</h1> +<h2 id="reverse-relations">Reverse relations</h2> +<p>Note that reverse relationships are not automatically included by the <code>ModelSerializer</code> and <code>HyperlinkedModelSerializer</code> classes. To include a reverse relationship, you must explicitly add it to the fields list. For example:</p> +<pre class="prettyprint lang-py"><code>class AlbumSerializer(serializers.ModelSerializer): + class Meta: + fields = ('tracks', ...) +</code></pre> +<p>You'll normally want to ensure that you've set an appropriate <code>related_name</code> argument on the relationship, that you can use as the field name. For example:</p> +<pre class="prettyprint lang-py"><code>class Track(models.Model): + album = models.ForeignKey(Album, related_name='tracks') + ... +</code></pre> +<p>If you have not set a related name for the reverse relationship, you'll need to use the automatically generated related name in the <code>fields</code> argument. For example:</p> +<pre class="prettyprint lang-py"><code>class AlbumSerializer(serializers.ModelSerializer): + class Meta: + fields = ('track_set', ...) +</code></pre> +<p>See the Django documentation on <a href="https://docs.djangoproject.com/en/dev/topics/db/queries/#following-relationships-backward">reverse relationships</a> for more details.</p> +<h2 id="generic-relationships">Generic relationships</h2> +<p>If you want to serialize a generic foreign key, you need to define a custom field, to determine explicitly how you want serialize the targets of the relationship.</p> +<p>For example, given the following model for a tag, which has a generic relationship with other arbitrary models:</p> +<pre class="prettyprint lang-py"><code>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 +</code></pre> +<p>And the following two models, which may be have associated tags:</p> +<pre class="prettyprint lang-py"><code>class Bookmark(models.Model): + """ + A bookmark consists of a URL, and 0 or more descriptive tags. + """ + url = models.URLField() + tags = GenericRelation(TaggedItem) + + +class Note(models.Model): + """ + A note consists of some text, and 0 or more descriptive tags. + """ + text = models.CharField(max_length=1000) + tags = GenericRelation(TaggedItem) +</code></pre> +<p>We could define a custom field that could be used to serialize tagged instances, using the type of each instance to determine how it should be serialized.</p> +<pre class="prettyprint lang-py"><code>class TaggedObjectRelatedField(serializers.RelatedField): + """ + A custom field to use for the `tagged_object` generic relationship. + """ + + def to_native(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') +</code></pre> +<p>If you need the target of the relationship to have a nested representation, you can use the required serializers inside the <code>.to_native()</code> method:</p> +<pre class="prettyprint lang-py"><code> def to_native(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): + serializer = NoteSerializer(value) + else: + raise Exception('Unexpected type of tagged object') + + return serializer.data +</code></pre> +<p>Note that reverse generic keys, expressed using the <code>GenericRelation</code> field, can be serialized using the regular relational field types, since the type of the target in the relationship is always known.</p> +<p>For more information see <a href="https://docs.djangoproject.com/en/dev/ref/contrib/contenttypes/#id1">the Django documentation on generic relations</a>.</p> +<h2 id="manytomanyfields-with-a-through-model">ManyToManyFields with a Through Model</h2> +<p>By default, relational fields that target a <code>ManyToManyField</code> with a +<code>through</code> model specified are set to read-only.</p> +<p>If you explicitly specify a relational field pointing to a +<code>ManyToManyField</code> with a through model, be sure to set <code>read_only</code> +to <code>True</code>.</p> +<h2 id="advanced-hyperlinked-fields">Advanced Hyperlinked fields</h2> +<p>If you have very specific requirements for the style of your hyperlinked relationships you can override <code>HyperlinkedRelatedField</code>. </p> +<p>There are two methods you'll need to override.</p> +<h4 id="get_urlself-obj-view_name-request-format">get_url(self, obj, view_name, request, format)</h4> +<p>This method should return the URL that corresponds to the given object.</p> +<p>May raise a <code>NoReverseMatch</code> if the <code>view_name</code> and <code>lookup_field</code> +attributes are not configured to correctly match the URL conf.</p> +<h4 id="get_objectself-queryset-view_name-view_args-view_kwargs">get_object(self, queryset, view_name, view_args, view_kwargs)</h4> +<p>This method should the object that corresponds to the matched URL conf arguments.</p> +<p>May raise an <code>ObjectDoesNotExist</code> exception.</p> +<h3 id="example_2">Example</h3> +<p>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: </p> +<pre class="prettyprint lang-py"><code>class CustomHyperlinkedField(serializers.HyperlinkedRelatedField): + def get_url(self, obj, view_name, request, format): + kwargs = {'account': obj.account, 'slug': obj.slug} + return reverse(view_name, kwargs=kwargs, request=request, format=format) + + 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=slug) +</code></pre> +<hr /> +<h2 id="deprecated-apis">Deprecated APIs</h2> +<p>The following classes have been deprecated, in favor of the <code>many=<bool></code> syntax. +They continue to function, but their usage will raise a <code>PendingDeprecationWarning</code>, which is silent by default.</p> +<ul> +<li><code>ManyRelatedField</code></li> +<li><code>ManyPrimaryKeyRelatedField</code></li> +<li><code>ManyHyperlinkedRelatedField</code></li> +<li><code>ManySlugRelatedField</code></li> +</ul> +<p>The <code>null=<bool></code> flag has been deprecated in favor of the <code>required=<bool></code> flag. It will continue to function, but will raise a <code>PendingDeprecationWarning</code>.</p> +<p>In the 2.3 release, these warnings will be escalated to a <code>DeprecationWarning</code>, which is loud by default. +In the 2.4 release, these parts of the API will be removed entirely.</p> +<p>For more details see the <a href="../topics/2.2-announcement.html">2.2 release announcement</a>.</p> + </div><!--/span--> + </div><!--/row--> + </div><!--/.fluid-container--> + </div><!--/.body content--> + + <div id="push"></div> + </div><!--/.wrapper --> + + <footer class="span12"> + <p>Sponsored by <a href="http://dabapps.com/">DabApps</a>.</a></p> + </footer> + + <!-- Le javascript + ================================================== --> + <!-- Placed at the end of the document so the pages load faster --> + <script src="http://django-rest-framework.org/js/jquery-1.8.1-min.js"></script> + <script src="http://django-rest-framework.org/js/prettify-1.0.js"></script> + <script src="http://django-rest-framework.org/js/bootstrap-2.1.1-min.js"></script> + <script> + //$('.side-nav').scrollspy() + var shiftWindow = function() { scrollBy(0, -50) }; + if (location.hash) shiftWindow(); + window.addEventListener("hashchange", shiftWindow); + + $('.dropdown-menu').on('click touchstart', function(event) { + event.stopPropagation(); + }); + + // Dynamically force sidenav to no higher than browser window + $('.side-nav').css('max-height', window.innerHeight - 130); + + $(function(){ + $(window).resize(function(){ + $('.side-nav').css('max-height', window.innerHeight - 130); + }); + }); + </script> +</body></html> |