Opened 6 years ago

Closed 6 years ago

Last modified 6 years ago

#30287 closed Uncategorized (duplicate)

post_remove and post_add behave differently for m2m_changed

Reported by: nirmalraghavan Owned by: nobody
Component: Uncategorized Version: 2.1
Severity: Normal Keywords: signals
Cc: Triage Stage: Unreviewed
Has patch: no Needs documentation: no
Needs tests: no Patch needs improvement: no
Easy pickings: no UI/UX: no

Description

Consider the following Model,

class MyModel(models.Model):
    likes = models.ForeignKey(User)

Now if I add a user to the likes field as below,

myObj.likes.add(user)

my m2m_changed receiver method will be called in signals module with action post_add and pk_set as the User ID. If I try to add likes again with the same user and same above method, now post_add again called with pk_set as empty.

And when I try to remove the user as below,

myObj.likes.remove(user)

m2m_changed receiver method is called with action post_remove and pk_set as User ID. And if I try to remove the same user again, this time also m2m_changed receiver method is called. But this time pk_set contains the User ID.

For post_add, pk_set will be empty after first add. Subsequent calls will always set pk_set as empty. But for post_remove pk_set will always contains pk_set value. Why it is that?

I'm calculating points based on this like events. Now I need to make sure ManyToMany relationship exist before adding/substracting points by making an extra call to database. If somehow we could know if the relation already added/removed from m2m_changed signal, it will be great.

Change History (1)

comment:1 by nirmalraghavan, 6 years ago

Resolution: duplicate
Status: newclosed

Duplicate of #29615.

Last edited 6 years ago by Tim Graham (previous) (diff)
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