Django's ManyToMany field can be populated using my_field.add(my_instance), but as I understand it only my_instance.id is actually needed to perform the corresponding SQL query.
If I want to add an object by its id, I can use my_field.add(MyModel.objects.get(id=id)), but this will generate two queries instead of one. How can I avoid this extra query?
Although the documentation of the add method does not mention it, you can actually pass directly an id to it, like this:
my_instance.add(id)
Surely, this only works when the primary key is used as the identifier for the relation (the default behaviour).
来源：https://stackoverflow.com/questions/37511421/add-an-object-by-id-in-a-manytomany-relation-in-django