pre_save is not called before the overridden save() method on a model

[siddhi]

If I have a model where I override the save() method, then the pre_save signal is not sent before the save method is called.

Example:

class MyModel(models.Model):
    name = models.CharField(max_length=20)

    def save(self, force_insert=False, force_update=False):
        if self.name == "dont_save":
            return
        super(Project, self).save(force_insert, force_delete)

def presave_handler(sender, instance, **kwargs):
    instance.name = "dont_save"

signals.pre_save.connect(presave_handler, sender=MyModel, dispatch_uid="abc")

In the above case, the flow goes like this

1. call overridden save method
2. check the condition in save method (condition is false)
3. call super
4. call pre_save
5. set name to "dont_save"
6. object saved to database with name = "dont_save"

This is rather unintuitive that the pre_save gets called in the middle of the save method. Also, any processing done in the pre_save cannot be handled in the save method as the flow has gone to the super class by then.

The expected flow should be like this

1. call overridden save method
2. call pre_save
3. set name to "dont_save"
4. execution enters save method
5. check condition in overridden save method (condition is true)
6. return without saving

[Karen Tracey]

(Fixed formatting. Note you've got to put a space before the 1. in your lists to get them to format properly.)

The signals doc: ​http://docs.djangoproject.com/en/dev/ref/signals/#module-django.db.models.signals

notes that if you override save() you must call the parent class method in order for the signals to be sent. That makes it pretty clear the parent class code is what is going to send the signals. It isn't clear to me how you expect a signal to get sent at step 2 here:

1. call overridden save method
2. call pre_save
3. set name to "dont_save".

At that point execution is in your own code, how is Django supposed to cause a signal to be sent?