Clarify dumpdata behavior and docs for custom serializers with internal_use_only flag

[ksauder]

As displayed in the diff, the code was simply broken and always raised an exception for custom serializer formats.

After further investigation, this problem could also be solved by adding 'internal_use_only = False' to the classes in the example here ​https://docs.djangoproject.com/en/5.2/topics/serialization/#custom-serialization-formats. This gets around the "if format in serializers.get_public_serializer_formats()" check, although the old code in the diff still doesn't make sense.

[David Sanders]

Hi there,

The code isn't broken, the exception should always be raised. The loop is there to provide the chance to raise a more appropriate message rather than "Unknown serialization format".

FYI this information was obtained by simply looking at git blame 👍

[ksauder]

Well, the code is a little broken. It doesn't actually raise a more appropriate message, and the docs do not actually point out that internal_use_only flag must be unset for it to work from the command line. I would suggest a change along the lines of this:

diff --git a/django/core/management/commands/dumpdata.py b/django/core/management/commands/dumpdata.py
index 15e615c1d0..9ec9ab76a3 100644
--- a/django/core/management/commands/dumpdata.py
+++ b/django/core/management/commands/dumpdata.py
@@ -177,9 +177,8 @@ class Command(BaseCommand):
             try:
                 serializers.get_serializer(format)
             except serializers.SerializerDoesNotExist:
-                pass
-
-            raise CommandError("Unknown serialization format: %s" % format)
+                raise CommandError("Unknown serialization format: %s" % format)
+            # We found it, but it's not a public serializer. Let the user know
+            raise CommandError("Serialization format %s is flagged for internal_use_only. Set internal_use_only = False in the Serializer to use it here." % format)
 
         def get_objects(count_only=False):
             """

And/or call out the internal_use_only flag near the custom serialization doc and its affect on CLI operation.

[David Sanders]

Doc updates are always welcome 👍 feel free to submit a doc PR for clarification if you like. Also if you feel the error message is lacking you're welcome to submit a PR for that too.

Just FYI you don't necessarily need a ticket for minor docs updates or minor code clarification (for future reference)

[ksauder]

Rog, I'll put one together

[Natalia Bidart]

Reopening to track the docs clarifications. Also downgrading to not release blocker.

[Sarah Boyce]

Please mark "Has patch" once a PR is open to our GitHub repository ​https://github.com/django/django