improve error when attempting to use a swapped model

[Preston Holmes]

Currently two checks for a swapped model exist when creating a manager:

• ​https://github.com/django/django/blob/3b6f980bedbbf091fe29bececa2b262d2084ce4d/django/db/models/manager.py#L16
• ​https://github.com/django/django/blob/3b6f980bedbbf091fe29bececa2b262d2084ce4d/django/db/models/manager.py#L61

These result in an error:

AttributeError: type object 'User' has no attribute 'objects'

as opposed to DatabaseError: no such table: <...> which is the error when the model is swapped but has the default manager (as syncdb will not create tables for swapped models). Ideally - there should be a manager installed that just raises an error explaining that the model has been swapped and is unavailable and probably offer information about what model it was swapped for - as this is readily available.

[Russell Keith-Magee <russell@…>]

In cc337a74f1808b216fff96f1695d8b066d2636f6:

Fixed #19069 -- Improved the error message when trying to query a swapped model.

Thanks to Preston Holmes for the suggestion.