migration: Add argument or flag which indicates the current db

[Kadir]

State:
Two DB's which should have all the same models.

Problem:
Running a RunPython migration on the second database fails since it still operates on the default database.

python manage.py migrate --database=seconddb

Except the hacky way, reading the sys.argv, there is no way to determine the current db to act upon that db.

Solution:
Add a parameter (or extend an existing) to include a variable "database" which contains the current db.
apps.get_model should be able to get the schema for a specific db.

[Tim Graham]

Use schema_editor.connection.alias to find the specified database as documented in the ​RunPython reference.

[Kadir]

My humblest apology for asking prematurely!