#35641: Pattern matching on model objects
-------------------------------------+-------------------------------------
Reporter: jdahlin | Owner: (none)
Type: New feature | Status: new
Component: Database layer | Version: 5.0
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Description changed by jdahlin:
Old description:
> 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.
>
> {{{#!python
> class Person(Model):
> name = TextField(...)
> age = IntegerField(...)
>
> class Company(Model):
> address = TextField(...)
> }}}
>
> I would then be able to do
> {{{#!python
> @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
> }}}
>
> The implementation for this is fairly straight-forward, add this to
> models.Model.
>
> {{{#!python
> @property
> def __match_args__(self) -> tuple[str, ...]:
> return tuple(f.name for f in self._meta.get_fields())
> }}}
>
> Happy to create a PR if this is interesting.
New description:
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.
{{{#!python
class Person(Model):
name = TextField(...)
age = IntegerField(...)
class Company(Model):
address = TextField(...)
}}}
I would then be able to do
{{{#!python
@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
}}}
Since __match_args__ must be a tuple, the attribute must be generated
inside a metaclass.
~~{{{#!python
@property
def __match_args__(self) -> tuple[str, ...]:
return tuple(f.name for f in self._meta.get_fields())
}}}~~
Happy to create a PR if this is interesting.
--
--
Ticket URL: <https://code.djangoproject.com/ticket/35641#comment:2>
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