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Diffstat (limited to 'docs/api-guide/serializers.md')
| -rw-r--r-- | docs/api-guide/serializers.md | 128 |
1 files changed, 88 insertions, 40 deletions
diff --git a/docs/api-guide/serializers.md b/docs/api-guide/serializers.md index 47958fe3..0cdae1ce 100644 --- a/docs/api-guide/serializers.md +++ b/docs/api-guide/serializers.md @@ -47,7 +47,7 @@ The first part of serializer class defines the fields that get serialized/deseri We can now use `CommentSerializer` to serialize a comment, or list of comments. Again, using the `Serializer` class looks a lot like using a `Form` class. - serializer = CommentSerializer(instance=comment) + serializer = CommentSerializer(comment) serializer.data # {'email': u'leila@example.com', 'content': u'foo bar', 'created': datetime.datetime(2012, 8, 22, 16, 20, 9, 822774)} @@ -65,18 +65,54 @@ Deserialization is similar. First we parse a stream into python native datatype ...then we restore those native datatypes into a fully populated object instance. - serializer = CommentSerializer(data) + serializer = CommentSerializer(data=data) serializer.is_valid() # True serializer.object # <Comment object at 0x10633b2d0> >>> serializer.deserialize('json', stream) +When deserializing data, we can either create a new instance, or update an existing instance. + + serializer = CommentSerializer(data=data) # Create new instance + serializer = CommentSerializer(comment, data=data) # Update `instance` + ## Validation When deserializing data, you always need to call `is_valid()` before attempting to access the deserialized object. If any validation errors occur, the `.errors` and `.non_field_errors` properties will contain the resulting error messages. -**TODO: Describe validation in more depth** +### Field-level validation + +You can specify custom field-level validation by adding `.validate_<fieldname>` methods to your `Serializer` subclass. These are analagous to `.clean_<fieldname>` methods on Django forms, but accept slightly different arguments. + +They take a dictionary of deserialized attributes as a first argument, and the field name in that dictionary as a second argument (which will be either the name of the field or the value of the `source` argument to the field, if one was provided). + +Your `validate_<fieldname>` methods should either just return the `attrs` dictionary or raise a `ValidationError`. For example: + + from rest_framework import serializers + + class BlogPostSerializer(serializers.Serializer): + title = serializers.CharField(max_length=100) + content = serializers.CharField() + + def validate_title(self, attrs, source): + """ + Check that the blog post is about Django. + """ + value = attrs[source] + if "django" not in value.lower(): + raise serializers.ValidationError("Blog post is not about Django") + return attrs + +### Object-level validation + +To do any other validation that requires access to multiple fields, add a method called `.validate()` to your `Serializer` subclass. This method takes a single argument, which is the `attrs` dictionary. It should raise a `ValidationError` if necessary, or just return `attrs`. + +## Saving object state + +Serializers also include a `.save()` method that you can override if you want to provide a method of persisting the state of a deserialized object. The default behavior of the method is to simply call `.save()` on the deserialized object instance. + +The generic views provided by REST framework call the `.save()` method when updating or creating entities. ## Dealing with nested objects @@ -86,21 +122,21 @@ where some of the attributes of an object might not be simple datatypes such as The `Serializer` class is itself a type of `Field`, and can be used to represent relationships where one object type is nested inside another. class UserSerializer(serializers.Serializer): - email = serializers.EmailField() - username = serializers.CharField() - - def restore_object(self, attrs, instance=None): - return User(**attrs) - + email = serializers.Field() + username = serializers.Field() class CommentSerializer(serializers.Serializer): user = UserSerializer() - title = serializers.CharField() - content = serializers.CharField(max_length=200) - created = serializers.DateTimeField() - - def restore_object(self, attrs, instance=None): - return Comment(**attrs) + title = serializers.Field() + content = serializers.Field() + created = serializers.Field() + +--- + +**Note**: Nested serializers are only suitable for read-only representations, as there are cases where they would have ambiguous or non-obvious behavior if used when updating instances. For read-write representations you should always use a flat representation, by using one of the `RelatedField` subclasses. + +--- + ## Creating custom fields @@ -114,7 +150,6 @@ Let's look at an example of serializing a class that represents an RGB color val """ A color represented in the RGB colorspace. """ - def __init__(self, red, green, blue): assert(red >= 0 and green >= 0 and blue >= 0) assert(red < 256 and green < 256 and blue < 256) @@ -124,7 +159,6 @@ Let's look at an example of serializing a class that represents an RGB color val """ Color objects are serialized into "rgb(#, #, #)" notation. """ - def to_native(self, obj): return "rgb(%d, %d, %d)" % (obj.red, obj.green, obj.blue) @@ -156,7 +190,7 @@ As an example, let's create a field that can be used represent the class name of # ModelSerializers Often you'll want serializer classes that map closely to model definitions. -The `ModelSerializer` class lets you automatically create a Serializer class with fields that corrospond to the Model fields. +The `ModelSerializer` class lets you automatically create a Serializer class with fields that correspond to the Model fields. class AccountSerializer(serializers.ModelSerializer): class Meta: @@ -169,13 +203,13 @@ The `ModelSerializer` class lets you automatically create a Serializer class wit You can add extra fields to a `ModelSerializer` or override the default fields by declaring fields on the class, just as you would for a `Serializer` class. class AccountSerializer(serializers.ModelSerializer): - url = CharField(source='get_absolute_url', readonly=True) + url = CharField(source='get_absolute_url', read_only=True) group = NaturalKeyField() class Meta: model = Account -Extra fields can corrospond to any property or callable on the model. +Extra fields can correspond to any property or callable on the model. ## Relational fields @@ -187,7 +221,7 @@ The `PrimaryKeyRelatedField` and `HyperlinkedRelatedField` fields provide altern The `ModelSerializer` class can itself be used as a field, in order to serialize relationships using nested representations. -The `RelatedField` class may be subclassed to create a custom represenation of a relationship. The subclass should override `.to_native()`, and optionally `.from_native()` if deserialization is supported. +The `RelatedField` class may be subclassed to create a custom representation of a relationship. The subclass should override `.to_native()`, and optionally `.from_native()` if deserialization is supported. All the relational fields may be used for any relationship or reverse relationship on a model. @@ -204,40 +238,54 @@ For example: ## Specifiying nested serialization -The default `ModelSerializer` uses primary keys for relationships, but you can also easily generate nested representations using the `nested` option: +The default `ModelSerializer` uses primary keys for relationships, but you can also easily generate nested representations using the `depth` option: class AccountSerializer(serializers.ModelSerializer): class Meta: model = Account exclude = ('id',) - nested = True + depth = 1 -The `nested` option may be set to either `True`, `False`, or an integer value. If given an integer value it indicates the depth of relationships that should be traversed before reverting to a flat representation. +The `depth` option should be set to an integer value that indicates the depth of relationships that should be traversed before reverting to a flat representation. -When serializing objects using a nested representation any occurances of recursion will be recognised, and will fall back to using a flat representation. +## Customising the default fields -## Customising the default fields used by a ModelSerializer +You can create customized subclasses of `ModelSerializer` that use a different set of default fields for the representation, by overriding various `get_<field_type>_field` methods. +Each of these methods may either return a field or serializer instance, or `None`. +### get_pk_field - class AccountSerializer(serializers.ModelSerializer): - class Meta: - model = Account +**Signature**: `.get_pk_field(self, model_field)` - def get_pk_field(self, model_field): - return serializers.Field(readonly=True) +Returns the field instance that should be used to represent the pk field. - def get_nested_field(self, model_field): - return serializers.ModelSerializer() +### get_nested_field - def get_related_field(self, model_field, to_many=False): - queryset = model_field.rel.to._default_manager - if to_many: - return return serializers.ManyRelatedField(queryset=queryset) - return serializers.RelatedField(queryset=queryset) +**Signature**: `.get_nested_field(self, model_field)` + +Returns the field instance that should be used to represent a related field when `depth` is specified as being non-zero. + +### get_related_field + +**Signature**: `.get_related_field(self, model_field, to_many=False)` + +Returns the field instance that should be used to represent a related field when `depth` is not specified, or when nested representations are being used and the depth reaches zero. + +### get_field + +**Signature**: `.get_field(self, model_field)` + +Returns the field instance that should be used for non-relational, non-pk fields. + +### Example: + +The following custom model serializer could be used as a base class for model serializers that should always exclude the pk by default. + + class NoPKModelSerializer(serializers.ModelSerializer): + def get_pk_field(self, model_field): + return None - def get_field(self, model_field): - return serializers.ModelField(model_field=model_field) [cite]: https://groups.google.com/d/topic/django-users/sVFaOfQi4wY/discussion |