Add the database alias to InconsistentMigrationHistory message

[Alexander Holmbäck]

In the file django/core/management/commands/makemigrations.py (line 97-100), an instance of MigrationLoader (loader) checks consistency on every database connection defined in settings.py.

for db in connections:
    connection = connection[db]
    if connection.settings_dict['ENGINE'] != 'django.db.backends.dummy':
        loader.check_consistent_history(connection)

The loader will then raise an InconsistentMigrationHistory exception for a connection whose migrations is not applied consistently, even if it's not to participate in the migration process.

I didn't expect makemigrations would check connections that isn't to be migrated. Also, the error message "Migration xxx is applied before its dependency xxx" (line 285 in db/migrations/loader.py) didn't indicate checked connection.

A more intuitive behavior would be to check only the connection that is to be migrated, or, if that isn't possible, include connection name in the error message.

[Tim Graham]

makemigrations doesn't run "per database" so that's why all connections are checked.

Accepting on the basis that the database alias should appear in the message. Thanks for that suggestion.

​PR