Mathesar Unable to Retrieve Records from Database

[MrChadMWood]

Description

Mathesar is unable to retrieve records, winds up saying no records found.

Expected behavior

Records should be retrieved without error and displayed. If an error does occur, maybe it is better to indicate this from the frontend instead of just showing "No Records Found".

To Reproduce

I am unsure what caused the issue. Please see the additional context.

Environment

• OS: Linux
• Browser: Firefox
• Other info: This appears to be a serverside error.

Additional context

Log statement of the error:

ERROR:django.request:Internal Server Error: /api/db/v0/tables/393/records/
Traceback (most recent call last):
  File "/usr/local/lib/python3.9/site-packages/django/core/handlers/exception.py", line 47, in inner
    response = get_response(request)
  File "/usr/local/lib/python3.9/site-packages/django/core/handlers/base.py", line 181, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/usr/local/lib/python3.9/site-packages/django/views/decorators/csrf.py", line 54, in wrapped_view
    return view_func(*args, **kwargs)
  File "/usr/local/lib/python3.9/site-packages/rest_framework/viewsets.py", line 125, in view
    return self.dispatch(request, *args, **kwargs)
  File "/usr/local/lib/python3.9/site-packages/rest_framework/views.py", line 509, in dispatch
    response = self.handle_exception(exc)
  File "/usr/local/lib/python3.9/site-packages/rest_framework/views.py", line 466, in handle_exception
    response = exception_handler(exc, context)
  File "/code/mathesar/exception_handlers.py", line 59, in mathesar_exception_handler
    raise exc
  File "/usr/local/lib/python3.9/site-packages/rest_framework/views.py", line 506, in dispatch
    response = handler(request, *args, **kwargs)
  File "/code/mathesar/api/db/viewsets/records.py", line 73, in list
    records = paginator.paginate_queryset(
  File "/code/mathesar/api/pagination.py", line 88, in paginate_queryset
    preview_metadata, preview_columns = get_preview_info(table.id)
  File "/code/mathesar/utils/preview.py", line 93, in get_preview_info
    preview_info, columns = _preview_info_by_column_id(
  File "/code/mathesar/utils/preview.py", line 14, in _preview_info_by_column_id
    for fk_constraint in fk_constraints:
  File "/code/mathesar/utils/preview.py", line 113, in _filter_out_circular_dependency_columns
    referent_column = fk_constraint.referent_columns[0]
  File "/usr/local/lib/python3.9/site-packages/django/db/models/query.py", line 325, in __getitem__
    return qs._result_cache[0]
IndexError: list index out of range

Without better knowledge of Mathesar's internal operations, it looks to me like qs._result_cache is an empty list- causing this error to be thrown. I'm not sure how or why the list would be empty.

Image of error from frontend:

[MrChadMWood]

Not sure if it matters, but those blocked requests appear to be blocked due to lack of encryption.

[seancolsen]

Thanks for reporting this, @MrChadMWood. Just a brief heads up that all maintainers will be on holiday break until January 2nd. We'll help troubleshoot this with you when we return!

[seancolsen]

@Anish9901 I've assigned this to you because I think we need a maintainer to look into this and try to reproduce it or better understand it. Can you spend some time with it and report back with your findings and recommendations for next steps?

[Anish9901]

@MrChadMWood Does the issue persist after clicking 'Sync External Changes' button on the database page?

Regardless of whether this fixes the issue, it would be great if you could provide a mock data model of the schema within which the error occurs, as it is difficult to pinpoint the cause of the error by looking at the error logs.

[mathemancer]

It looks like a Constraint model instance representing a foreign key has ended up in an inconsistent state w.r.t. its linked (referent) Column model instances.

[seancolsen]

@MrChadMWood are you still encountering this?

I'm trying to move this issue along. We're not able to reproduce this, and it looks like we need some more info from you before we're able to help.

Was this bug just a fluke that you never saw again?

• I so, how would you feel about closing this issue? It's worth noting that we are currently overhauling our backend architecture and moving towards a system that should make bugs like this far less likely.

• If you are still able to reproduce it, then:

  • We'd like to know if "Sync External Changes" has any effect.
  • We'd like to know more about your schema. It would be helpful if you could give us a pg_dump --schema-only SQL file so we can see the entire structure.

[seancolsen]

@MrChadMWood since we haven't heard from you in a while about this, I'm going to close it. We'll be happy to re-open it if we can get some more info to help our troubleshooting efforts. It's also worth mentioning that we're in the process of a substantial backend overhaul that will bring many stability improvements for Mathesar's beta release later this year. Hopefully bugs like this will go away on their own!