id column is created in ManyToMany link (relation) table
|Reported by:||Evgeniy Ivanov||Owned by:||nobody|
|Component:||Database layer (models, ORM)||Version:||master|
|Cc:||Triage Stage:||Design decision needed|
|Has patch:||yes||Needs documentation:||no|
|Needs tests:||no||Patch needs improvement:||yes|
When I use ManyToManyField, extra id field is created for link (relation) table. It's done in sql_for_many_to_many_field() function.
I didn't find any comment in the source code or anything in the docs/google, so it might be a bug rather than intentional behavior.