Allow mass-update of fields in unpersisted model instances

[Yoong Kang Lim]

Sometimes we have an unpersisted model instance generated from, say, a factory. Before saving this to the database, we might want to do some additional processing to update the fields.

I think it's a good idea to provide a helper method in the Model class to mass update the fields, particularly if it's a model with many fields.

[Tim Graham]

Could you give an example of the API you have in mind?

[Yoong Kang Lim]

Yep. I have a pull request on GitHub, but basically the method should take a dictionary where the keys are the names of the field, and the values are the updated field values.

This code snippet should do the trick:

def assign_attributes(self, values_dict):
    keys = values_dict.keys()
    fields = [f.name for f in self._meta.get_fields()]
    for k in keys:
        if k in fields:
            setattr(self, k, values_dict[k])

There is a similar method in Rails which I'm used to using:
​http://api.rubyonrails.org/classes/ActiveRecord/AttributeAssignment.html

[Tim Graham]

I don't like the idea of silently ignoring values from values_dict if they don't existing in fields. It seems this would make typos more difficult to debug.

Overall, I don't have a strong opinion on whether or not this should be part of Django, so I'd suggest to write to the DevelopersMailingList to get some opinions. However, if we get rid of the fields logic, it seems this boils down to two lines:

for k, v in values_dict.items():
    setattr(instance, k, v)

so the value of adding a method for that doesn't seem significant. Of course, you can create a model mixin if you really want it in your own project.