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Add disabling of declared fields on serializer subclasses (#4764)
* Add test for disabling declared fields on child * Check that declared base field is not in attrs * Update meta inheritance docs to include serializer * Test that meta fields cannot be declared as None * Add docs example for declarative field disabling
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@ -578,16 +578,6 @@ Alternative representations include serializing using hyperlinks, serializing co
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For full details see the [serializer relations][relations] documentation.
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## Inheritance of the 'Meta' class
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The inner `Meta` class on serializers is not inherited from parent classes by default. This is the same behavior as with Django's `Model` and `ModelForm` classes. If you want the `Meta` class to inherit from a parent class you must do so explicitly. For example:
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class AccountSerializer(MyBaseSerializer):
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class Meta(MyBaseSerializer.Meta):
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model = Account
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Typically we would recommend *not* using inheritance on inner Meta classes, but instead declaring all options explicitly.
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## Customizing field mappings
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The ModelSerializer class also exposes an API that you can override in order to alter how serializer fields are automatically determined when instantiating the serializer.
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@ -1025,6 +1015,40 @@ If any of the validation fails, then the method should raise a `serializers.Vali
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The `data` argument passed to this method will normally be the value of `request.data`, so the datatype it provides will depend on the parser classes you have configured for your API.
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## Serializer Inheritance
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Similar to Django forms, you can extend and reuse serializers through inheritance. This allows you to declare a common set of fields or methods on a parent class that can then be used in a number of serializers. For example,
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class MyBaseSerializer(Serializer):
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my_field = serializers.CharField()
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def validate_my_field(self):
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...
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class MySerializer(MyBaseSerializer):
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...
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Like Django's `Model` and `ModelForm` classes, the inner `Meta` class on serializers does not implicitly inherit from it's parents' inner `Meta` classes. If you want the `Meta` class to inherit from a parent class you must do so explicitly. For example:
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class AccountSerializer(MyBaseSerializer):
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class Meta(MyBaseSerializer.Meta):
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model = Account
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Typically we would recommend *not* using inheritance on inner Meta classes, but instead declaring all options explicitly.
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Additionally, the following caveats apply to serializer inheritance:
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* Normal Python name resolution rules apply. If you have multiple base classes that declare a `Meta` inner class, only the first one will be used. This means the child’s `Meta`, if it exists, otherwise the `Meta` of the first parent, etc.
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* It’s possible to declaratively remove a `Field` inherited from a parent class by setting the name to be `None` on the subclass.
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class MyBaseSerializer(ModelSerializer):
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my_field = serializers.CharField()
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class MySerializer(MyBaseSerializer):
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my_field = None
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However, you can only use this technique to opt out from a field defined declaratively by a parent class; it won’t prevent the `ModelSerializer` from generating a default field. To opt-out from default fields, see [Specifying which fields to include](#specifying-which-fields-to-include).
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## Dynamically modifying fields
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Once a serializer has been initialized, the dictionary of fields that are set on the serializer may be accessed using the `.fields` attribute. Accessing and modifying this attribute allows you to dynamically modify the serializer.
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@ -305,7 +305,11 @@ class SerializerMetaclass(type):
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# in order to maintain the correct order of fields.
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for base in reversed(bases):
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if hasattr(base, '_declared_fields'):
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fields = list(base._declared_fields.items()) + fields
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fields = [
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(field_name, obj) for field_name, obj
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in base._declared_fields.items()
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if field_name not in attrs
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] + fields
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return OrderedDict(fields)
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@ -7,6 +7,8 @@ import re
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import pytest
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from django.db import models
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from rest_framework import fields, relations, serializers
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from rest_framework.compat import unicode_repr
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from rest_framework.fields import Field
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@ -413,3 +415,42 @@ class Test4606Regression:
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serializer = self.Serializer(data=[{"name": "liz"}], many=True)
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with pytest.raises(serializers.ValidationError):
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serializer.is_valid(raise_exception=True)
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class TestDeclaredFieldInheritance:
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def test_declared_field_disabling(self):
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class Parent(serializers.Serializer):
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f1 = serializers.CharField()
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f2 = serializers.CharField()
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class Child(Parent):
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f1 = None
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class Grandchild(Child):
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pass
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assert len(Parent._declared_fields) == 2
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assert len(Child._declared_fields) == 1
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assert len(Grandchild._declared_fields) == 1
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def test_meta_field_disabling(self):
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# Declaratively setting a field on a child class will *not* prevent
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# the ModelSerializer from generating a default field.
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class MyModel(models.Model):
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f1 = models.CharField(max_length=10)
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f2 = models.CharField(max_length=10)
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class Parent(serializers.ModelSerializer):
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class Meta:
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model = MyModel
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fields = ['f1', 'f2']
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class Child(Parent):
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f1 = None
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class Grandchild(Child):
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pass
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assert len(Parent().get_fields()) == 2
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assert len(Child().get_fields()) == 2
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assert len(Grandchild().get_fields()) == 2
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