Use the str representation of a queryset instead of the __repr__

This way, if the serializer is inadvertently converted to a string, the
queryset won't be executed.

rest_framework/utils/representation.py

@@ -23,10 +23,17 @@ def manager_repr(value):
     return repr(value)
 
 
+def queryset_repr(queryset):
+    return "{}".format(queryset.query)
+
+
 def smart_repr(value):
     if isinstance(value, models.Manager):
         return manager_repr(value)
 
+    if isinstance(value, models.QuerySet):
+        value = queryset_repr(value)
+
     if isinstance(value, Promise) and value._delegate_text:
         value = force_str(value)
 

tests/test_model_serializer.py

@@ -23,7 +23,7 @@ from django.db.models.signals import m2m_changed
 from django.dispatch import receiver
 from django.test import TestCase
 
-from rest_framework import serializers
+from rest_framework import serializers, fields
 from rest_framework.compat import postgres_fields
 
 from .models import NestedForeignKeySource
@@ -559,6 +559,18 @@ class TestRelationalFieldMappings(TestCase):
         """)
         self.assertEqual(repr(TestSerializer()), expected)
 
+    def test_manual_pk_relation_will_customize_queryset_repr_to_avoid_execute_it(self):
+        queryset = ForeignKeyTargetModel.objects.all()
+
+        class TestSerializer(serializers.Serializer):
+            field = serializers.PrimaryKeyRelatedField(queryset=queryset)
+
+        expected = dedent("""
+            TestSerializer():
+                field = PrimaryKeyRelatedField(queryset='{}')
+        """)
+        self.assertEqual(repr(TestSerializer()), expected.format(queryset.query))
+
     def test_nested_relations(self):
         class TestSerializer(serializers.ModelSerializer):
             class Meta: