I am using a custom primary key for a model that has a few ManyToManyFields. When I update the model and add an object to a ManyToManyField (using add(new_object)), I get an error signifying that its looking up the primary key using the id field (which perhaps exists in the intermediary table, but not in the model).
psycopg2.DataError: invalid input syntax for integer: "TL98GK"
LINE 1: ...WHERE ("placedir_place_place_categ"."place_id" = 'TL98GK' A...
I have been searching on SO for a while but havent been able to zero in the exact issue. I guess I may have to use custom through table for ManytoManyFields (as a punishment for using custom primary key) but I honestly dont want to go down that route.
Using Django 1.10 and Python 3
It seems the migration doesn't detect Foreign Key type changes well. It's a known bug. A workaround is mentioned here (i.e to explicitly change the field type to varchar(32)).
However, you may need to do more (like updating the constraints etc. on the table) depending on your use case. (For those interested to go that route, here is one example case with corresponding migration code).
(p.s I just decided to not use a custom primary key on models with manytomany fields)