9.8 KiB
Serializer fields
Flat is better than nested.
Serializer fields handle converting between primative values and internal datatypes. They also deal with validating input values, as well as retrieving and setting the values from their parent objects.
Note: The serializer fields are declared in fields.py, but by convention you should import them using from rest_framework import serializers
and refer to fields as serializers.<FieldName>
.
Core arguments
Each serializer field class constructor takes at least these arguments. Some Field classes take additional, field-specific arguments, but the following should always be accepted:
source
The name of the attribute that will be used to populate the field. May be a method that only takes a self
argument, such as Field(source='get_absolute_url')
, or may use dotted notation to traverse attributes, such as Field(source='user.email')
.
The value source='*'
has a special meaning, and is used to indicate that the entire object should be passed through to the field. This can be useful for creating nested representations. (See the implementation of the PaginationSerializer
class for an example.)
Defaults to the name of the field.
read_only
Set this to True
to ensure that the field is used when serializing a representation, but is not used when updating an instance dureing deserialization.
Defaults to False
required
Normally an error will be raised if a field is not supplied during deserialization. Set to false if this field is not required to be present during deserialization.
Defaults to True
.
default
If set, this gives the default value that will be used for the field if none is supplied. If not set the default behaviour is to not populate the attribute at all.
validators
A list of Django validators that should be used to validate deserialized values.
error_messages
A dictionary of error codes to error messages.
widget
Used only if rendering the field to HTML. This argument sets the widget that should be used to render the field.
Generic Fields
These generic fields are used for representing arbitrary model fields or the output of model methods.
Field
A generic, read-only field. You can use this field for any attribute that does not need to support write operations.
For example, using the following model.
class Account(models.Model):
owner = models.ForeignKey('auth.user')
name = models.CharField(max_length=100)
created = models.DateTimeField(auto_now_add=True)
payment_expiry = models.DateTimeField()
def has_expired(self):
now = datetime.datetime.now()
return now > self.payment_expiry
A serializer definition that looked like this:
class AccountSerializer(serializers.HyperlinkedModelSerializer):
expired = Field(source='has_expired')
class Meta:
fields = ('url', 'owner', 'name', 'expired')
Would produce output similar to:
{
'url': 'http://example.com/api/accounts/3/',
'owner': 'http://example.com/api/users/12/',
'name': 'FooCorp business account',
'expired': True
}
By default, the Field
class will perform a basic translation of the source value into primative datatypes, falling back to unicode representations of complex datatypes when necessary.
You can customize this behaviour by overriding the .to_native(self, value)
method.
WritableField
A field that supports both read and write operations. By itself WriteableField
does not perform any translation of input values into a given type. You won't typically use this field directly, but you may want to override it and implement the .to_native(self, value)
and .from_native(self, value)
methods.
ModelField
A generic field that can be tied to any arbitrary model field. The ModelField
class delegates the task of serialization/deserialization to it's associated model field. This field can be used to create serializer fields for custom model fields, without having to create a new custom serializer field.
Signature: ModelField(model_field=<Django ModelField class>)
Typed Fields
These fields represent basic datatypes, and support both reading and writing values.
BooleanField
A Boolean representation.
Corresponds to django.db.models.fields.BooleanField
.
CharField
A text representation, optionally validates the text to be shorter than max_length
and longer than min_length
.
Corresponds to django.db.models.fields.CharField
or django.db.models.fields.TextField
.
Signature: CharField(max_length=None, min_length=None)
ChoiceField
A field that can accept a value out of a limited set of choices.
EmailField
A text representation, validates the text to be a valid e-mail address.
Corresponds to django.db.models.fields.EmailField
DateField
A date representation.
Corresponds to django.db.models.fields.DateField
DateTimeField
A date and time representation.
Corresponds to django.db.models.fields.DateTimeField
IntegerField
An integer representation.
Corresponds to django.db.models.fields.IntegerField
, django.db.models.fields.SmallIntegerField
, django.db.models.fields.PositiveIntegerField
and django.db.models.fields.PositiveSmallIntegerField
FloatField
A floating point representation.
Corresponds to django.db.models.fields.FloatField
.
Relational Fields
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
.
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 customise this behaviour 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 read-write, although you can change this behaviour using the read_only
flag.
Arguments:
queryset
- All relational fields must either set a queryset, or setread_only=True
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 behaviour using the read_only
flag.
Arguments:
slug_field
- The field on the target that should be used for representation. This should be a field that uniquely identifies any given instance. For example,username
.queryset
- All relational fields must either set a queryset, or setread_only=True
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 behaviour 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 theformat
argument.queryset
- All relational fields must either set a queryset, or setread_only=True
slug_url_kwarg
- The named url parameter for the slug field lookup. Default isslug
slug_field
- The field on the target that should be used for the lookup. Default isslug
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 theformat
argument.