Recommend note identifying that post_save signals will be fired on loaddata

[brandon@…]

On: ​https://docs.djangoproject.com/en/dev/ref/django-admin/#loaddata-fixture-fixture

It says the following:

• When fixture files are processed, the data is saved to the database as is. Model defined save methods and pre_save signals are not called.

However, it does not make specific mention about other signals. Recommend making the text explicit so that readers understand that other signals not mentioned here will be called (post_save et al).

Example:

Let's say you're testing on a local server and you have use post_save to send emails or other notifications. loaddata will resend all emails on load. This is behaviour that, in a test environment, one may wish to avoid.

Related: https://code.djangoproject.com/ticket/8399

[Tim Graham]

Added a patch which also attempts to address #13299 since it's related.

[brandon@…]

Just looking at the diff, I asked a similar question to 8399 and 13299. The answer suggested creating a decorator to block the signal from loaddata. Seems like it may be a better solution than increasing cyclomatic complexity in signal functions.

Source: ​http://stackoverflow.com/questions/15624817/have-loaddata-ignore-or-disable-post-save-signals/15625121#15625121

from functools import wraps
def disable_for_loaddata(signal_handler):
    """
    Decorator that turns off signal handlers when loading fixture data.
    """

    @wraps(signal_handler)
    def wrapper(*args, **kwargs):
        if kwargs['raw']:
            return
        signal_handler(*args, **kwargs)
    return wrapper
Then:

@disable_for_loaddata
def your_fun(**kwargs):
    ## stuff that won't happen if the signal is initiated by loaddata process

[Anssi Kääriäinen]

If I am not mistaken both pre_save and post_save signals will be sent. There is a raw argument to the signal that can be used to detect when loaddata (or any other method wishing to insert the values as-is to the DB). See ​https://docs.djangoproject.com/en/dev/ref/signals/#django.db.models.signals.pre_save.

It seems the loaddata docs are currently plain wrong.

[Tim Graham]

I wouldn't be opposed to documenting the decorator method as I've used it before as well.

[brandon@…]

That decorator creates some unintended consequences when used in conjunction with django-tastypie (API POST calls skip signals with that decorator). Perhaps not entirely relevant here, but "nice to know".

[Tim Graham]

Anssi is correct, I've fixed that inaccuracy and added the decorator example.

[Tim Graham <timograham@…>]

In 2c62a509deb50e39375b0cd44cfc85a743978fdc:

Fixed #20136 - Fixed and expanded the docs for loaddata and model signals.

Thanks brandon@ and Anssi for the report.

[Tim Graham <timograham@…>]

In 18a2fb19074ce6789639b62710c279a711dabf97:

[1.5.X] Fixed #20136 - Fixed and expanded the docs for loaddata and model signals.

Thanks brandon@ and Anssi for the report.

Backport of 2c62a509de from master