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

Serializer fields

Flat is better than nested.

— The Zen of Python

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.

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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>.

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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.

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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>)

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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)

URLField

Corresponds to django.db.models.fields.URLField. Uses Django's django.core.validators.URLValidator for validation.

Signature: CharField(max_length=200, min_length=None)

SlugField

Corresponds to django.db.models.fields.SlugField.

Signature: CharField(max_length=50, 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.

FileField

A file representation. Performs Django's standard FileField validation.

Corresponds to django.forms.fields.FileField.

Signature: FileField(max_length=None, allow_empty_file=False)

• max_length designates the maximum length for the file name.

• allow_empty_file designates if empty files are allowed.

ImageField

An image representation.

Corresponds to django.forms.fields.ImageField.

Requires the PIL package.

Signature and validation is the same as with FileField.

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Note: FileFields and ImageFields are only suitable for use with MultiPartParser, since eg json doesn't support file uploads. Django's regular FILE_UPLOAD_HANDLERS are used for handling uploaded files.

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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 are read-write, although you can change this behaviour 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.

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 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.

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 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.

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.

Other Fields

SerializerMethodField

This is a read-only field. It gets its value by calling a method on the serializer class it is attached to. It can be used to add any sort of data to the serialized representation of your object. The field's constructor accepts a single argument, which is the name of the method on the serializer to be called. The method should accept a single argument (in addition to self), which is the object being serialized. It should return whatever you want to be included in the serialized representation of the object. For example:

from rest_framework import serializers
from django.contrib.auth.models import User
from django.utils.timezone import now

class UserSerializer(serializers.ModelSerializer):

    days_since_joined = serializers.SerializerMethodField('get_days_since_joined')

    class Meta:
        model = User

    def get_days_since_joined(self, obj):
        return (now() - obj.date_joined).days