Unique field - _perform_unique_checks problem

[arannasousa]

Sorry for the bad English (translated via Google).

I have a correction suggest.

Currently working with different database without be 'default'.
One of my classes has a field with the 'unique = True' on.

When trying to make the register for a new item, via django.forms.ModelForm, page back me an error: "Database of not exists" (because is other database)

This was why the django was to perform a query from behind, to see if there is not any registered item that is equal to, but he did not know which database to look.

My suggestion is as follows:

version: 'development'
the file: 'django.db.models.base.py'
lines: 1006 and 1043

change from:

qs = model_class._default_manager.filter(**lookup_kwargs)

to:

qs = model_class._default_manager.using(getattr(self, 'db', None)).filter(**lookup_kwargs)

Thus, problems with UNIQUE fields in different banks 'default' ended

[Tim Graham]

Looks like a duplicate of #15130.