Uniqueness validation

rest_framework/fields.py

@@ -150,6 +150,10 @@ class Field(object):
         messages.update(error_messages or {})
         self.error_messages = messages
 
+        for validator in validators:
+            if getattr(validator, 'requires_context', False):
+                validator.serializer_field = self
+
     def bind(self, field_name, parent):
         """
         Initializes the field name and parent for the field instance.

rest_framework/utils/field_mapping.py

@@ -6,6 +6,7 @@ from django.core import validators
 from django.db import models
 from django.utils.text import capfirst
 from rest_framework.compat import clean_manytomany_helptext
+from rest_framework.validators import UniqueValidator
 import inspect
 
 
@@ -156,6 +157,10 @@ def get_field_kwargs(field_name, model_field):
             if validator is not validators.validate_slug
         ]
 
+    if getattr(model_field, 'unique', False):
+        validator = UniqueValidator(queryset=model_field.model._default_manager)
+        validator_kwarg.append(validator)
+
     max_digits = getattr(model_field, 'max_digits', None)
     if max_digits is not None:
         kwargs['max_digits'] = max_digits

rest_framework/validators.py

@@ -0,0 +1,57 @@
+from django.core.exceptions import ValidationError
+
+
+class UniqueValidator:
+    # Validators with `requires_context` will have the field instance
+    # passed to them when the field is instantiated.
+    requires_context = True
+
+    def __init__(self, queryset):
+        self.queryset = queryset
+        self.serializer_field = None
+
+    def get_queryset(self):
+        return self.queryset.all()
+
+    def __call__(self, value):
+        field = self.serializer_field
+
+        # Determine the model field name that the serializer field corresponds to.
+        field_name = field.source_attrs[0] if field.source_attrs else field.field_name
+
+        # Determine the existing instance, if this is an update operation.
+        instance = getattr(field.parent, 'instance', None)
+
+        # Ensure uniqueness.
+        filter_kwargs = {field_name: value}
+        queryset = self.get_queryset().filter(**filter_kwargs)
+        if instance:
+            queryset = queryset.exclude(pk=instance.pk)
+        if queryset.exists():
+            raise ValidationError('This field must be unique.')
+
+
+class UniqueTogetherValidator:
+    requires_context = True
+
+    def __init__(self, queryset, fields):
+        self.queryset = queryset
+        self.fields = fields
+        self.serializer_field = None
+
+    def __call__(self, value):
+        serializer = self.serializer_field
+
+        # Determine the existing instance, if this is an update operation.
+        instance = getattr(serializer, 'instance', None)
+
+        # Ensure uniqueness.
+        filter_kwargs = dict([
+            (field_name, value[field_name]) for field_name in self.fields
+        ])
+        queryset = self.get_queryset().filter(**filter_kwargs)
+        if instance:
+            queryset = queryset.exclude(pk=instance.pk)
+        if queryset.exists():
+            field_names = ' and '.join(self.fields)
+            raise ValidationError('The fields %s must make a unique set.' % field_names)

tests/test_validators.py

@@ -0,0 +1,35 @@
+from django.db import models
+from django.test import TestCase
+from rest_framework import serializers
+
+
+class ExampleModel(models.Model):
+    username = models.CharField(unique=True, max_length=100)
+
+
+class ExampleSerializer(serializers.ModelSerializer):
+    class Meta:
+        model = ExampleModel
+
+
+class TestUniquenessValidation(TestCase):
+    def setUp(self):
+        self.instance = ExampleModel.objects.create(username='existing')
+
+    def test_is_not_unique(self):
+        data = {'username': 'existing'}
+        serializer = ExampleSerializer(data=data)
+        assert not serializer.is_valid()
+        assert serializer.errors == {'username': ['This field must be unique.']}
+
+    def test_is_unique(self):
+        data = {'username': 'other'}
+        serializer = ExampleSerializer(data=data)
+        assert serializer.is_valid()
+        assert serializer.validated_data == {'username': 'other'}
+
+    def test_updated_instance_excluded(self):
+        data = {'username': 'existing'}
+        serializer = ExampleSerializer(self.instance, data=data)
+        assert serializer.is_valid()
+        assert serializer.validated_data == {'username': 'existing'}