Change model-object at PUT and update before GET in django-rest-framework

Question

Sorry about the confusing title, but I don't know how to describe it better.

I need to run a model-function on the object I am editing using PUT in Django-Rest-Framework, which uses some of the new data from the PUT to calculate some new values it should save in the same model.

Example:

• An item with {'amount': 2, 'price': 0, 'total': 0} is already stored in the database.
• I am then updating price to 1 using a normal PUT request using django-rest-framework.
• The model have a helperfunction called update_total() which I need to call to update the total field in the database (to, in this case 2 (2*1)).
• The item is updated in the database, but the response returned from django-rest-framework is still showing total=0. After getting the object on new, total will be 2 as expected.

I need the response to be 2 in the response from the PUT, not after a regrab of the object. But how?

I have tried several things (which all doesn’t work):

• Updating attrs in a validator to the new value.
• Using post_save() in ListCreateAPIView to update the data.
• Using pre_save() in ListCreateAPIView
• Updating instance in restore_object() (even though it isn't for this purpose)

Does this look like a bug? Or is there another trick?

Answer 1

I kinda found a solution, but it feels somewhat dirty..

In my serializers restore_object I put code like this:

new_values = instance.update_counters()
for k, v in new_values.items():
    self.data[k] = v

and in my models update_counters() function, I am returning a dict of what I changed..