change IntegrityError to DatabaseError

[27medkamal]

Sometimes, Django raises a DatabaseError instead of an IntegrityError when duplicates are found.

Reference here

[iceone]

Hi! Thanks for your PR!
But could you give more details of your use case?
When it raises such exception?

[27medkamal]

I did some debugging and that seems to happen when update_fields is used which is used in the save method by django-mptt
In a simple use case, an IntegrityError is raised but in more complex scenarios a DatabaseError seems to be raised instead.

[valignatev]

I guess that it theoretically could pass update_fields while creating new model instance somewhere in the tree: https://github.com/django-mptt/django-mptt/blob/85ff21fb93b61071dcb4cdc4bfc25e886f9ad486/mptt/models.py#L982

[iceone]

The main problem I see -- in your case when DatabaseError is raised there is no additional information passed to it. So we can't determine what field caused unique constraint violation to perform another try to regenerate UID.
And therefore in most cases DatabaseError will mean any error not related with UIDField.

Anyway, we need more detailed use case description to make appropriate fix (how to reproduce this bug).