MongoEngine / MongoEngine/mongoengine
Trying to access field value raises object has no attribute '_get_db' when using MapField and LazyReferenceField
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Description
Given a Document with:
some_field = MapField(field=LazyReferenceField(SomeOtherDocument, dbref=True))
Setting and saving some_field works correctly. But accessing the field after fetching the document yields:
File "/usr/local/lib/python3.8/dist-packages/mongoengine/base/fields.py", line 329, in __get__
value = _dereference(value, max_depth=1, instance=instance, name=self.name)
File "/usr/local/lib/python3.8/dist-packages/mongoengine/dereference.py", line 97, in __call__
self.object_map = self._fetch_objects(doc_type=doc_type)
File "/usr/local/lib/python3.8/dist-packages/mongoengine/dereference.py", line 189, in _fetch_objects
references = doc_type._get_db()[collection].find(
AttributeError: 'LazyReferenceField' object has no attribute '_get_db'
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Research direction
Reproduce the MapField with a LazyReferenceField configured with dbref=True, then trace the failure from mongoengine/base/fields.py into mongoengine/dereference.py as shown in the traceback. Confirm that fetching the document and accessing the mapped field no longer raises the _get_db AttributeError, and add or run focused regression coverage if the repository provides it.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- mongodb, python
- Domain
- database
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 30/100