django TransactionManagementError when using signals

Question

I have a one to one field with django's users and UserInfo. I want to subscribe to the post_save callback function on the user model so that I can then save the UserInfo as well. ``` @receiver(post_save, sender=User) def saveUserAndInfo(sender, instance, **kwargs): user = instance try: user.user_info.save() except: info = UserInfo() info.user = user info.save() ``` However, I am getting a `TransactionManagementError` when I try to do this. I am assuming because the user model hasn't finished saving and I am trying to read the id to save it to the user_info. Anyone know how to do this properly? A second problem. I wanted to attach a UserInfo instance to a user as soon as the user was created. So on post_init I tried to create a UserInfo instance and assign it to the user instance but it doesn't work because the user hasn't been assigned a pk yet. I am assuming I just have to wait until post_save (or later) to create this instance. Is this the only way to do it? Traceback: ``` File "/Us…

Accepted Answer

The error is caused by the `user.user_info.save()` line throwing an exception, and the transaction was flagged as broken (PostgreSQL enforces rolling back either the whole transaction, or to any savepoint stored before doing any more queries inside that transaction).

You can rollback the transaction when an error occurs:

```
from django.db import IntegrityError, transaction

@receiver(post_save, sender=User) 
def saveUserAndInfo(sender, instance, **kwargs):
    user = instance
    try:
        with transaction.atomic():
            user.user_info.save()
    except IntegrityError:
        info = UserInfo()
        info.user = user
        info.save()
```

This is greatly described in the documentation.

Also, note that catching all exception types is not generally the best idea as you might silence exceptions you weren't expecting.

django TransactionManagementError when using signals

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