[Django]-ValueError – Cannot assign: must be an instance

by

75👍

✅

You don’t need to pass the department id, the instance itself is enough.

The following should work just fine:

new_team = Team(
    nickname = team_name,
    employee_id = employee_id,
    department_id = Department.objects.get(password = password,
                                           department_name = department_name))

Just a note: don’t ever name your foreign fields something_id.

That something is enough. Django is meant to make things easy from the user’s perspective and the _id suffix means you’re thinking of the database layer. In fact, if you named your column department, django will automatically create department_id column in the database for you.

The way things are, you’re making Django create department_id_id which is rather silly.

👤Anonymous

13👍

This came up first on a Google search so offering an alternative for newcomers. You can also do it this way in case you have handy access to the id and don’t want to do another query:

new_team = Team(
    nickname = team_name,
    employee_id = employee_id,
    department_id_id = Department.objects.get(password = password, department_name = department_name).department_id
)

In short, {foreign_key_name}_id if you want to assign the id directly.

👤munsu

0👍

A different variant for @munsu ‘s answer. If you already have the id for the foreign field.

department_id = 2; #the department id for the new team

new_team = Team(
    nickname = team_name,
    employee_id = employee_id,
    department_id = Department(id=department_id)
)

new_team.save()

# but
new_team.department_id.id # 2 
new_team.department_id.department_name # None you cannot access any other fields

I don’t know if this would be useful for any case, but here it is. 🙂

👤Sagar Devkota

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