django-computedfields 0.0.21

autoupdated database fields for model methods

django-computedfields

django-computedfields provides autoupdated database fields for model methods.

Tested with Django 2.2 and 3.0 (Python 3.6 to 3.8).

Example

Just derive your model from ComputedFieldsModel and place the @computed decorator at a method:

from django.db import models
from computedfields.models import ComputedFieldsModel, computed

class MyModel(ComputedFieldsModel):
    name = models.CharField(max_length=32)

    @computed(models.CharField(max_length=32), depends=[['self', ['name']]])
    def computed_field(self):
        return self.name.upper()

computed_field will be turned into a real database field and can be accessed and searched like any other database field. During saving the associated method gets called and it’s result written to the database. With the method compute('fieldname') you can inspect the value that will be written, which is useful if you have pending changes:

>>> person = MyModel(forename='berty')
>>> person.computed_field             # empty since not saved yet
>>> person.compute('computed_field')  # outputs 'BERTY'
>>> person.save()
>>> person.computed_field             # outputs 'BERTY'

The depends keyword argument can be used with any relation to indicate dependencies to fields on other models as well:

from django.db import models
from computedfields.models import ComputedFieldsModel, computed

class MyModel(ComputedFieldsModel):
    name = models.CharField(max_length=32)
    fk = models.ForeignKey(SomeModel)

    @computed(models.CharField(max_length=32), depends=[['self', ['name']], ['fk', ['fieldname']]])
    def computed_field(self):
        return self.name.upper() + self.fk.fieldname

Now changes to self.name or fk.fieldname will update computed_field.

NOTE: The old depends syntax is deprecated and should be replaced with the new syntax. It also should contain a self entry with local fields to get reliable updates from local field changes. This is especially true for advanced usage with save(update_fields=[...]) or bulk actions. The old syntax will be removed with a future version.

Documentation

The documentation can be found here.