Django models, custom functions

Question

I am creating a simple application with Django. I realized that I am doing the same kind of operations very often. For example I often need to get all Article objects which have isPublick = True. So I am wondering, is it possible to define a get_published function in the model?

If the model looks like this (simplified)

class Article(models.Model):
    title = models.CharField(...)
    isPublished = models.BooleandField()

    def get_active(self):
       return Article.objects.filter(isPublicshed = 1)

But this doesn't seem to work.

Can you suggest a way of implementing the function?

Umang · Accepted Answer · 2011-07-14 20:04:52Z

87

What you probably want is a custom manager

From the django docs:

        # An example of a custom manager called "objects".

class PersonManager(models.Manager):
    def get_fun_people(self):
        return self.filter(fun=True)

class Person(models.Model):
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=30)
    fun = models.BooleanField()
    objects = PersonManager()

    def __unicode__(self):
        return u"%s %s" % (self.first_name, self.last_name)

which then allows you to do something like:

>>> p1 = Person(first_name='Bugs', last_name='Bunny', fun=True)
>>> p1.save()
>>> p2 = Person(first_name='Droopy', last_name='Dog', fun=False)
>>> p2.save()
>>> Person.objects.get_fun_people()
[<Person: Bugs Bunny>]

edited Jul 14, 2011 at 20:04

Umang

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answered Sep 3, 2009 at 8:07

aciniglio

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2 Comments

chucksmash Over a year ago

Good code example. Succinctly explained a part of django that previously seemed pointless to me (in my noobosity). +1.

muditrustagii Over a year ago

It is also worth mentioning, that in order for this to work and avoid NameErrors, you need to write the manager class above the object class, for it to recognize it.

Yash · Accepted Answer · 2020-04-01 09:21:46Z

24

As is stated in the docs here, if you need to add custom row-level functionality to your objects, you need to define custom methods on your models. However, if what you are after is custom table-wide functionality (such as getting all Article objects that qualify certain conditions), you have to define custom methods on model Managers (much as aciniglio above points out in their answer).

edited Apr 1, 2020 at 9:21

Yash

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answered Sep 3, 2009 at 8:20

ayaz

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Comments

ruohola · Accepted Answer · 2019-09-02 15:26:20Z

20

You can use the staticmethod decorator.

class Article(models.Model):
    title = models.CharField(...)
    isPublished = models.BooleandField()

    @staticmethod
    def get_active():
        return Article.objects.filter(isPublished = 1)

edited Sep 2, 2019 at 15:26

ruohola

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answered Sep 3, 2009 at 8:27

David

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2 Comments

alexsalo Over a year ago

Thanks for bringing this up! Answered my, different, question.

Sven Marnach Over a year ago

This should be a classmethod instead.

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