django-rest-framework/docs/api-guide/relations.md

Serializer relations

Bad programmers worry about the code. Good programmers worry about data structures and their relationships.

— Linus Torvalds

Relational fields are used to represent model relationships. They can be applied to ForeignKey, ManyToManyField and OneToOneField relationships, as well as to reverse relationships, and custom relationships such as GenericForeignKey.

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Note: The relational fields are declared in relations.py, but by convention you should import them using from rest_framework import serializers and refer to fields as serializers.<FieldName>.

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RelatedField

This field can be applied to any of the following:

• A ForeignKey field.
• A OneToOneField field.
• A reverse OneToOne relationship
• Any other "to-one" relationship.

By default RelatedField will represent the target of the field using it's __unicode__ method.

You can customize this behavior by subclassing ManyRelatedField, and overriding the .to_native(self, value) method.

ManyRelatedField

This field can be applied to any of the following:

• A ManyToManyField field.
• A reverse ManyToMany relationship.
• A reverse ForeignKey relationship
• Any other "to-many" relationship.

By default ManyRelatedField will represent the targets of the field using their __unicode__ method.

For example, given the following models:

class TaggedItem(models.Model):
    """
    Tags arbitrary model instances using a generic relation.
    
    See: https://docs.djangoproject.com/en/dev/ref/contrib/contenttypes/
    """
    tag = models.SlugField()
    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField()
    content_object = GenericForeignKey('content_type', 'object_id')

    def __unicode__(self):
        return self.tag


class Bookmark(models.Model):
    """
    A bookmark consists of a URL, and 0 or more descriptive tags.
    """
    url = models.URLField()
    tags = GenericRelation(TaggedItem)

And a model serializer defined like this:

class BookmarkSerializer(serializers.ModelSerializer):
    tags = serializers.ManyRelatedField(source='tags')

    class Meta:
        model = Bookmark
        exclude = ('id',)

Then an example output format for a Bookmark instance would be:

{
    'tags': [u'django', u'python'],
    'url': u'https://www.djangoproject.com/'
}

PrimaryKeyRelatedField

ManyPrimaryKeyRelatedField

PrimaryKeyRelatedField and ManyPrimaryKeyRelatedField will represent the target of the relationship using it's primary key.

By default these fields are read-write, although you can change this behavior using the read_only flag.

Arguments:

• 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.
• null - If set to True, the field will accept values of None or the empty-string for nullable relationships.

SlugRelatedField

ManySlugRelatedField

SlugRelatedField and ManySlugRelatedField will represent the target of the relationship using a unique slug.

By default these fields read-write, although you can change this behavior using the read_only flag.

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.
• 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.
• null - If set to True, the field will accept values of None or the empty-string for nullable relationships.

HyperlinkedRelatedField

ManyHyperlinkedRelatedField

HyperlinkedRelatedField and ManyHyperlinkedRelatedField will represent the target of the relationship using a hyperlink.

By default, HyperlinkedRelatedField is read-write, although you can change this behavior using the read_only flag.

Arguments:

• view_name - The view name that should be used as the target of the relationship. required.
• format - If using format suffixes, hyperlinked fields will use the same format suffix for the target unless overridden by using the format argument.
• 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.
• slug_field - The field on the target that should be used for the lookup. Default is 'slug'.
• pk_url_kwarg - The named url parameter for the pk field lookup. Default is pk.
• slug_url_kwarg - The named url parameter for the slug field lookup. Default is to use the same value as given for slug_field.
• null - If set to True, the field will accept values of None or the empty-string for nullable relationships.

HyperLinkedIdentityField

This field can be applied as an identity relationship, such as the 'url' field on a HyperlinkedModelSerializer.

This field is always read-only.

Arguments:

• view_name - The view name that should be used as the target of the relationship. required.
• format - If using format suffixes, hyperlinked fields will use the same format suffix for the target unless overridden by using the format argument.
• slug_field - The field on the target that should be used for the lookup. Default is 'slug'.
• pk_url_kwarg - The named url parameter for the pk field lookup. Default is pk.
• slug_url_kwarg - The named url parameter for the slug field lookup. Default is to use the same value as given for slug_field.