Deserializing CompositePrimaryKey from a string raises raises ValueError

[Jacob Walls]

Adjusting this test (for a roundtrip from a serialized string and back) to use CompositePrimaryKey produces a failure:

tests/serializers/models/base.py

@@ -99 +99 @@
 
 
 class Movie(models.Model):
+    pk = models.CompositePrimaryKey("actor", "title", "price")
     actor = models.ForeignKey(Actor, models.CASCADE)
     title = models.CharField(max_length=50)
     price = models.DecimalField(max_digits=6, decimal_places=2, default=Decimal("0.00"))

ERROR: test_serialize_unicode_roundtrip (serializers.test_xml.XmlSerializerTestCase.test_serialize_unicode_roundtrip)
Unicode makes the roundtrip intact
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/.../django/tests/serializers/tests.py", line 241, in test_serialize_unicode_roundtrip
    obj_list = list(serializers.deserialize(self.serializer_name, serial_str))
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/.../django/django/core/serializers/xml_serializer.py", line 214, in __next__
    return self._handle_object(node)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/.../django/django/core/serializers/xml_serializer.py", line 289, in _handle_object
    obj = base.build_instance(Model, data, self.db)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/.../django/django/core/serializers/base.py", line 325, in build_instance
    return Model(**data)
           ^^^^^^^^^^^^^
  File "/Users/.../django/django/db/models/base.py", line 566, in __init__
    _setattr(self, prop, value)
  File "/Users/.../django/django/db/models/fields/composite.py", line 36, in __set__
    raise ValueError(f"{self.field.name!r} must be a list or a tuple.")
ValueError: 'pk' must be a list or a tuple.

----------------------------------------------------------------------
Ran 212 tests in 7.973s

FAILED (errors=1)

Other unit tests using other test models fail if adjusted in the same way, so this is not isolated to the xml serializer.

[Sarah Boyce]

Thank you!

[Jacob Walls]

Thanks for jumping on this, Sarah. This was buried at the bottom of the ticket, but there is a similar issue with the JSON and YAML serializers. For example, adjusting this test model fails produces more failures. Would you prefer a new ticket?

tests/serializers/models/base.py

@@ -150 +150 @@
 
 
 class Player(models.Model):
+    pk = models.CompositePrimaryKey("name", "rank", "team")
     name = models.CharField(max_length=50)
     rank = models.IntegerField()
     team = TeamField()

[Sarah Boyce]

Ah sorry I missed that, let's keep it as one ticket

[Simon Charette]

As pointed out on the PR we likely need to implement the proper value_to_string, value_from_object, and to_python methods for CompositePrimaryKey (​docs) and ensure the serialization framework calls value_to_string instead of making direct str calls.

See how it's done for JSONField, postgres.ArrayField, and HStoreField for example.

[Sarah Boyce <42296566+sarahboyce@…>]

In 6a1a9c0:

Fixed #36062 -- Handled serialization of CompositePrimaryKeys.