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Exclude read_only=True fields from unique_together validation & add docs. (#4192)
* Exclude read_only=True fields from unique_together validation * Test to ensure that unique_together validators can be removed * Do not add uniquness_extra_kwargs when validators are explicitly declared. * Add docs on validation in complex cases
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@ -156,7 +156,7 @@ If you want the date field to be entirely hidden from the user, then use `Hidden
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---
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# Advanced 'default' argument usage
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# Advanced field defaults
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Validators that are applied across multiple fields in the serializer can sometimes require a field input that should not be provided by the API client, but that *is* available as input to the validator.
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@ -188,6 +188,71 @@ It takes a single argument, which is the default value or callable that should b
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---
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# Limitations of validators
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There are some ambiguous cases where you'll need to instead handle validation
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explicitly, rather than relying on the default serializer classes that
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`ModelSerializer` generates.
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In these cases you may want to disable the automatically generated validators,
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by specifying an empty list for the serializer `Meta.validators` attribute.
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## Optional fields
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By default "unique together" validation enforces that all fields be
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`required=True`. In some cases, you might want to explicit apply
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`required=False` to one of the fields, in which case the desired behaviour
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of the validation is ambiguous.
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In this case you will typically need to exclude the validator from the
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serializer class, and instead write any validation logic explicitly, either
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in the `.validate()` method, or else in the view.
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For example:
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class BillingRecordSerializer(serializers.ModelSerializer):
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def validate(self, data):
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# Apply custom validation either here, or in the view.
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class Meta:
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fields = ('client', 'date', 'amount')
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extra_kwargs = {'client' {'required': 'False'}}
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validators = [] # Remove a default "unique together" constraint.
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## Updating nested serializers
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When applying an update to an existing instance, uniqueness validators will
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exclude the current instance from the uniqueness check. The current instance
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is available in the context of the uniqueness check, because it exists as
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an attribute on the serializer, having initially been passed using
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`instance=...` when instantiating the serializer.
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In the case of update operations on *nested* serializers there's no way of
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applying this exclusion, because the instance is not available.
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Again, you'll probably want to explicitly remove the validator from the
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serializer class, and write the code the for the validation constraint
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explicitly, in a `.validate()` method, or in the view.
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## Debugging complex cases
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If you're not sure exactly what behavior a `ModelSerializer` class will
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generate it is usually a good idea to run `manage.py shell`, and print
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an instance of the serializer, so that you can inspect the fields and
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validators that it automatically generates for you.
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>>> serializer = MyComplexModelSerializer()
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>>> print(serializer)
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class MyComplexModelSerializer:
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my_fields = ...
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Also keep in mind that with complex cases it can often be better to explicitly
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define your serializer classes, rather than relying on the default
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`ModelSerializer` behavior. This involves a little more code, but ensures
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that the resulting behavior is more transparent.
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---
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# Writing custom validators
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You can use any of Django's existing validators, or write your own custom validators.
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@ -1243,6 +1243,11 @@ class ModelSerializer(Serializer):
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read_only_fields = getattr(self.Meta, 'read_only_fields', None)
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if read_only_fields is not None:
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if not isinstance(read_only_fields, (list, tuple)):
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raise TypeError(
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'The `read_only_fields` option must be a list or tuple. '
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'Got %s.' % type(read_only_fields).__name__
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)
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for field_name in read_only_fields:
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kwargs = extra_kwargs.get(field_name, {})
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kwargs['read_only'] = True
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@ -1258,6 +1263,9 @@ class ModelSerializer(Serializer):
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('dict of updated extra kwargs', 'mapping of hidden fields')
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"""
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if getattr(self.Meta, 'validators', None) is not None:
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return (extra_kwargs, {})
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model = getattr(self.Meta, 'model')
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model_fields = self._get_model_fields(
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field_names, declared_fields, extra_kwargs
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@ -1308,7 +1316,7 @@ class ModelSerializer(Serializer):
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else:
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uniqueness_extra_kwargs[unique_constraint_name] = {'default': default}
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elif default is not empty:
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# The corresponding field is not present in the,
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# The corresponding field is not present in the
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# serializer. We have a default to use for it, so
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# add in a hidden field that populates it.
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hidden_fields[unique_constraint_name] = HiddenField(default=default)
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@ -1390,6 +1398,7 @@ class ModelSerializer(Serializer):
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field_names = {
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field.source for field in self.fields.values()
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if (field.source != '*') and ('.' not in field.source)
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and not field.read_only
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}
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# Note that we make sure to check `unique_together` both on the
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@ -521,8 +521,6 @@ class TestRelationalFieldMappings(TestCase):
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one_to_one = NestedSerializer(read_only=True):
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url = HyperlinkedIdentityField(view_name='onetoonetargetmodel-detail')
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name = CharField(max_length=100)
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class Meta:
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validators = [<UniqueTogetherValidator(queryset=UniqueTogetherModel.objects.all(), fields=('foreign_key', 'one_to_one'))>]
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""")
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if six.PY2:
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# This case is also too awkward to resolve fully across both py2
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@ -239,6 +239,45 @@ class TestUniquenessTogetherValidation(TestCase):
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""")
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assert repr(serializer) == expected
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def test_ignore_read_only_fields(self):
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"""
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When serializer fields are read only, then uniqueness
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validators should not be added for that field.
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"""
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class ReadOnlyFieldSerializer(serializers.ModelSerializer):
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class Meta:
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model = UniquenessTogetherModel
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fields = ('id', 'race_name', 'position')
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read_only_fields = ('race_name',)
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serializer = ReadOnlyFieldSerializer()
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expected = dedent("""
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ReadOnlyFieldSerializer():
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id = IntegerField(label='ID', read_only=True)
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race_name = CharField(read_only=True)
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position = IntegerField(required=True)
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""")
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assert repr(serializer) == expected
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def test_allow_explict_override(self):
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"""
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Ensure validators can be explicitly removed..
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"""
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class NoValidatorsSerializer(serializers.ModelSerializer):
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class Meta:
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model = UniquenessTogetherModel
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fields = ('id', 'race_name', 'position')
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validators = []
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serializer = NoValidatorsSerializer()
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expected = dedent("""
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NoValidatorsSerializer():
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id = IntegerField(label='ID', read_only=True)
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race_name = CharField(max_length=100)
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position = IntegerField()
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""")
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assert repr(serializer) == expected
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def test_ignore_validation_for_null_fields(self):
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# None values that are on fields which are part of the uniqueness
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# constraint cause the instance to ignore uniqueness validation.
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