Fixed #36062 -- Handled serialization of CompositePrimaryKeys.

django/core/serializers/xml_serializer.py

@@ -56,7 +56,7 @@ class Serializer(base.Serializer):
         if not self.use_natural_primary_keys or not hasattr(obj, "natural_key"):
             obj_pk = obj.pk
             if obj_pk is not None:
-                attrs["pk"] = str(obj_pk)
+                attrs["pk"] = obj._meta.pk.value_to_string(obj)
 
         self.xml.startElement("object", attrs)
 

django/db/models/fields/composite.py

@@ -1,3 +1,5 @@
+import json
+
 from django.core import checks
 from django.db.models import NOT_PROVIDED, Field
 from django.db.models.expressions import ColPairs
@@ -13,6 +15,11 @@ from django.db.models.fields.tuple_lookups import (
 from django.utils.functional import cached_property
 
 
+class AttributeSetter:
+    def __init__(self, name, value):
+        setattr(self, name, value)
+
+
 class CompositeAttribute:
     def __init__(self, field):
         self.field = field
@@ -130,6 +137,24 @@ class CompositePrimaryKey(Field):
             )
         ]
 
+    def value_to_string(self, obj):
+        values = []
+        vals = self.value_from_object(obj)
+        for field, value in zip(self.fields, vals):
+            obj = AttributeSetter(field.attname, value)
+            values.append(field.value_to_string(obj))
+        return json.dumps(values, ensure_ascii=False)
+
+    def to_python(self, value):
+        if isinstance(value, str):
+            # Assume we're deserializing.
+            vals = json.loads(value)
+            value = [
+                field.to_python(val)
+                for field, val in zip(self.fields, vals, strict=True)
+            ]
+        return value
+
 
 CompositePrimaryKey.register_lookup(TupleExact)
 CompositePrimaryKey.register_lookup(TupleGreaterThan)

tests/composite_pk/fixtures/tenant.json

@@ -71,5 +71,13 @@
             "tenant_id": 2,
             "id": "ffffffff-ffff-ffff-ffff-ffffffffffff"
         }
+    },
+    {
+        "pk": [1, "2022-01-12T05:55:14.956"],
+        "model": "composite_pk.timestamped",
+        "fields": {
+            "id": 1,
+            "created": "2022-01-12T05:55:14.956"
+        }
     }
 ]

tests/composite_pk/models/__init__.py

@@ -1,9 +1,10 @@
-from .tenant import Comment, Post, Tenant, Token, User
+from .tenant import Comment, Post, Tenant, TimeStamped, Token, User
 
 __all__ = [
     "Comment",
     "Post",
     "Tenant",
+    "TimeStamped",
     "Token",
     "User",
 ]

tests/composite_pk/models/tenant.py

@@ -48,3 +48,9 @@ class Post(models.Model):
     pk = models.CompositePrimaryKey("tenant_id", "id")
     tenant = models.ForeignKey(Tenant, on_delete=models.CASCADE)
     id = models.UUIDField()
+
+
+class TimeStamped(models.Model):
+    pk = models.CompositePrimaryKey("id", "created")
+    id = models.SmallIntegerField(unique=True)
+    created = models.DateTimeField(auto_now_add=True)

tests/composite_pk/tests.py

@@ -17,7 +17,7 @@ from django.db.models import CompositePrimaryKey
 from django.forms import modelform_factory
 from django.test import TestCase
 
-from .models import Comment, Post, Tenant, User
+from .models import Comment, Post, Tenant, TimeStamped, User
 
 
 class CommentForm(forms.ModelForm):
@@ -224,6 +224,13 @@ class CompositePKFixturesTests(TestCase):
         self.assertEqual(post_2.tenant_id, 2)
         self.assertEqual(post_2.pk, (post_2.tenant_id, post_2.id))
 
+    def assert_deserializer(self, format, users, serialized_users):
+        deserialized_user = list(serializers.deserialize(format, serialized_users))[0]
+        self.assertEqual(deserialized_user.object.email, users[0].email)
+        self.assertEqual(deserialized_user.object.id, users[0].id)
+        self.assertEqual(deserialized_user.object.tenant, users[0].tenant)
+        self.assertEqual(deserialized_user.object.pk, users[0].pk)
+
     def test_serialize_user_json(self):
         users = User.objects.filter(pk=(1, 1))
         result = serializers.serialize("json", users)
@@ -241,6 +248,7 @@ class CompositePKFixturesTests(TestCase):
                 }
             ],
         )
+        self.assert_deserializer(format="json", users=users, serialized_users=result)
 
     def test_serialize_user_jsonl(self):
         users = User.objects.filter(pk=(1, 2))
@@ -257,6 +265,7 @@ class CompositePKFixturesTests(TestCase):
                 },
             },
         )
+        self.assert_deserializer(format="jsonl", users=users, serialized_users=result)
 
     @unittest.skipUnless(HAS_YAML, "No yaml library detected")
     def test_serialize_user_yaml(self):
@@ -276,6 +285,7 @@ class CompositePKFixturesTests(TestCase):
                 },
             ],
         )
+        self.assert_deserializer(format="yaml", users=users, serialized_users=result)
 
     def test_serialize_user_python(self):
         users = User.objects.filter(pk=(2, 4))
@@ -294,6 +304,13 @@ class CompositePKFixturesTests(TestCase):
                 },
             ],
         )
+        self.assert_deserializer(format="python", users=users, serialized_users=result)
+
+    def test_serialize_user_xml(self):
+        users = User.objects.filter(pk=(1, 1))
+        result = serializers.serialize("xml", users)
+        self.assertIn('<object model="composite_pk.user" pk=\'["1", "1"]\'>', result)
+        self.assert_deserializer(format="xml", users=users, serialized_users=result)
 
     def test_serialize_post_uuid(self):
         posts = Post.objects.filter(pk=(2, "11111111-1111-1111-1111-111111111111"))
@@ -311,3 +328,27 @@ class CompositePKFixturesTests(TestCase):
                 },
             ],
         )
+
+    def test_serialize_datetime(self):
+        result = serializers.serialize("json", TimeStamped.objects.all())
+        self.assertEqual(
+            json.loads(result),
+            [
+                {
+                    "model": "composite_pk.timestamped",
+                    "pk": [1, "2022-01-12T05:55:14.956"],
+                    "fields": {
+                        "id": 1,
+                        "created": "2022-01-12T05:55:14.956",
+                    },
+                },
+            ],
+        )
+
+    def test_invalid_pk_extra_field(self):
+        json = (
+            '[{"fields": {"email": "user0001@example.com", "id": 1, "tenant": 1}, '
+            '"pk": [1, 1, "extra"], "model": "composite_pk.user"}]'
+        )
+        with self.assertRaises(serializers.base.DeserializationError):
+            next(serializers.deserialize("json", json))