How to determine if a field has changed in a Django modelform

Question

I was surprised that this was difficult to do. However I came up with this, which seems to work at least for my simple case. Can anyone recommend a better approach?

Answer 1

It seems that you have reinvented .has_changed() method.

Answer 2

Form contains a property changed_data which holds a list of all the fields whose values have changed.

Try:

'fieldname' in myforminstance.changed_data

Answer 3

Extending on Airs's answer, for multiple fields:

In a scenario where you'd like to track changes for a list of fields ['field_a', 'field_b', 'field_c']

---

If you'd like to check if any of those fields has changed:

any(x in myforminstance.changed_data for x in ['field_a', 'field_b', 'field_c'])

---

If you'd like to check if all of those fields have changed:

all(x in myforminstance.changed_data for x in ['field_a', 'field_b', 'field_c'])

Answer 4

You must override the method post_save. Overriding methods is a good practice in Django: https://docs.djangoproject.com/en/dev/ref/signals/#post-save

I suggest you adding something like this into your model class:

    def post_save(self, sender, instance, created, raw, using, update_fields):
        if 'the_field' in update_fields:
           # Do whatever...