ManyRelatedField.choices tries to iterate over None

[LilyFoote]

ManyRelatedField.choices is a property which iterates over self.child_relation.queryset. This can be None if self.child_relation is read-only.
I found this when SimpleMetadata.get_field_info tried to check if field.choices exists and raised TypeError.

[LilyFoote]

I'm not sure where the best place to fix this is. A simple fix for my direct issue would be to catch the TypeError in SimpleMetadata.get_field_info, but I'm not sure ManyRelatedField.choices should be raising it in the first place.

[adm271828]

I went into similar issue a few days ago. I got this when making an OPTIONS request and it seems the response tries to iterate over field choices, even if field is read only (which a simple GET resquest doesn't do).

I fixed this by adding (file: relations.py, line:380)

       iterable = queryset.all() if (hasattr(queryset, 'all')) else queryset
+      if not iterable:
+          return { }

This is perhaps a bad behaviour of the OPTION request that could check if field is not read_only before calling choices(). But, on the other hand, the choice method is not robust...

Best regards.

[jannon]

I've just run into this as well. I think the solution is definitely to change the behavior of the metadata so that it checks if the field is read_only. After all, there is no point in iterating over the choices for a read_only field. I'll submit a PR shortly