Display an empty label into related fields if it isn't required

rest_framework/relations.py

@@ -8,6 +8,7 @@ from __future__ import unicode_literals
 from django.core.exceptions import ObjectDoesNotExist, ValidationError
 from django.core.urlresolvers import resolve, get_script_prefix, NoReverseMatch
 from django import forms
+from django.db.models.fields import BLANK_CHOICE_DASH
 from django.forms import widgets
 from django.forms.models import ModelChoiceIterator
 from django.utils.translation import ugettext_lazy as _
@@ -47,7 +48,7 @@ class RelatedField(WritableField):
                           DeprecationWarning, stacklevel=2)
             kwargs['required'] = not kwargs.pop('null')
 
-        self.queryset = kwargs.pop('queryset', None)
+        queryset = kwargs.pop('queryset', None)
         self.many = kwargs.pop('many', self.many)
         if self.many:
             self.widget = self.many_widget
@@ -56,6 +57,11 @@ class RelatedField(WritableField):
         kwargs['read_only'] = kwargs.pop('read_only', self.read_only)
         super(RelatedField, self).__init__(*args, **kwargs)
 
+        if not self.required:
+            self.empty_label = BLANK_CHOICE_DASH[0][1]
+
+        self.queryset = queryset
+
     def initialize(self, parent, field_name):
         super(RelatedField, self).initialize(parent, field_name)
         if self.queryset is None and not self.read_only:

rest_framework/tests/serializer.py

@@ -1117,6 +1117,63 @@ class SerializerChoiceFields(TestCase):
         )
 
 
+# Regression tests for #675
+class Ticket(models.Model):
+    assigned = models.ForeignKey(
+        Person, related_name='assigned_tickets')
+    reviewer = models.ForeignKey(
+        Person, blank=True, null=True, related_name='reviewed_tickets')
+
+
+class SerializerRelatedChoicesTest(TestCase):
+
+    def setUp(self):
+        super(SerializerRelatedChoicesTest, self).setUp()
+
+        class RelatedChoicesSerializer(serializers.ModelSerializer):
+            class Meta:
+                model = Ticket
+                fields = ('assigned', 'reviewer')
+
+        self.related_fields_serializer = RelatedChoicesSerializer
+
+    def test_empty_queryset_required(self):
+        serializer = self.related_fields_serializer()
+        self.assertEqual(serializer.fields['assigned'].queryset.count(), 0)
+        self.assertEqual(
+            [x for x in serializer.fields['assigned'].widget.choices],
+            []
+        )
+
+    def test_empty_queryset_not_required(self):
+        serializer = self.related_fields_serializer()
+        self.assertEqual(serializer.fields['reviewer'].queryset.count(), 0)
+        self.assertEqual(
+            [x for x in serializer.fields['reviewer'].widget.choices],
+            [(u'', u'---------')]
+        )
+
+    def test_with_some_persons_required(self):
+        Person.objects.create(name="Lionel Messi")
+        Person.objects.create(name="Xavi Hernandez")
+        serializer = self.related_fields_serializer()
+        self.assertEqual(serializer.fields['assigned'].queryset.count(), 2)
+        self.assertEqual(
+            [x for x in serializer.fields['assigned'].widget.choices],
+            [(1, u'Person object - 1'), (2, u'Person object - 2')]
+        )
+
+    def test_with_some_persons_not_required(self):
+        Person.objects.create(name="Lionel Messi")
+        Person.objects.create(name="Xavi Hernandez")
+        serializer = self.related_fields_serializer()
+        self.assertEqual(serializer.fields['reviewer'].queryset.count(), 2)
+        self.assertEqual(
+            [x for x in serializer.fields['reviewer'].widget.choices],
+            [(u'', u'---------'), (1, u'Person object - 1'), (2, u'Person object - 2')]
+        )
+
+
 class DepthTest(TestCase):
     def test_implicit_nesting(self):