#21763: Misleading Error: 'ManyRelatedManager' object has no attribute 'add'
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Reporter: anonymous | Owner: nobody
Type: | Status: new
Cleanup/optimization | Version: master
Component: Database layer | Resolution:
(models, ORM) | Triage Stage: Accepted
Severity: Normal | Needs documentation: 0
Keywords: | Patch needs improvement: 0
Has patch: 0 | UI/UX: 0
Needs tests: 1 |
Easy pickings: 1 |
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Comment (by oflores):
Hi, it seems to be an expected behavior and very well documented. Here it
is part of the explanation from django doc.
https://docs.djangoproject.com/en/1.6/topics/db/models/#extra-fields-on-
many-to-many-relationships
"Unlike normal many-to-many fields, you can’t use add, create, or
assignment (i.e., beatles.members = [...]) to create relationships:
{{{
# THIS WILL NOT WORK
>>> beatles.members.add(john)
# NEITHER WILL THIS
>>> beatles.members.create(name="George Harrison")
# AND NEITHER WILL THIS
>>> beatles.members = [john, paul, ringo, george]
}}}
Why? You can’t just create a relationship between a Person and a Group -
you need to specify all the detail for the relationship required by the
Membership model. The simple add, create and assignment calls don’t
provide a way to specify this extra detail. As a result, they are disabled
for many-to-many relationships that use an intermediate model. The only
way to create this type of relationship is to create instances of the
intermediate model."
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Ticket URL: <https://code.djangoproject.com/ticket/21763#comment:3>
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