Pattern matching on model objects

[Johan Dahlin]

It would be nice if I could use pattern matching on Django model fields, this is especially important in context where I don't know what the model is, for example in a global post_save() handler where I want to do some specific logic based on a subclass.

class Person(Model):
    name = TextField(...)
    age = IntegerField(...)

class Company(Model):
    address = TextField(...)

I would then be able to do

@receiver(pre_save)
def pre_save(sender, instance, ....):
   # model comes in via signals or some other way, we don't know which subclass it is
   match model:
      # equivalent to isinstance(model, Person) and model.age > 10:
       case Person(age) if age> 10:
            ....
      # equivalent to isinstance(model, Company) and model.name.endswith('Street')
       case Company(address) if name.endswith('Street'):
            ....
       # or just extract and return a value
       case Person(name):
           return name

Happy to create a PR if this is interesting.

[Johan Dahlin]

I removed an earlier comment about a simple/straight-forward implementation using a @property but it won't work as, match_args needs to be a tuple and cannot be a property, so my suggested implementation above is too simplistic. I real one would have to be a bit more involved and generate the values and create a tuple inside the models metaclass.

[Simon Charette]

I think we'd have to see a PR and how invasive it is to implement before taking a decision here. I personally only see marginal readability gains in the example you provided so I'm skeptical that's worth the complexity.

[Natalia Bidart]

Hello Johan, welcome to the Django Community! Nice to see you again.

I personally like your proposal, but since Django is a community driven project, there is a established procedure to request new features which requires first gathering community consensus so then a ticket can be accepted. To do that, please consider starting a new conversation on the ​Django Forum, where you'll reach a wider audience and likely get extra feedback.

I'll close the ticket for now, but if there is a community agreement for the feature request, you are welcome to come back to the ticket and point to the forum topic, so we can then re-open it. For more details, please see ​the documented guidelines for requesting features.

Thanks!