Automatically assigning model field values in Django

Question

Is there a way to automatically set field values for models in Django when defining the model? This could be used for storing something like a timestamp (for example), but also for creating a field which is constructed as some function of the others.

In other words, I'm looking for something like this:

class Foo(models.Model):

spam = models.CharField(max_length=2000)
my_other_field = ###?

def generate_my_other_field():
    #Some algorithm to determine the value of my_other_field

Do you want to store these generated values in the database? Or just have them available when you're looking at the model instances? — Gareth
– Gareth, Commented Jul 10, 2011 at 21:01
I'd like to generate them when the other fields are defined as well - basically, the way an initializer would work in Python. There might be a cleaner way to do this, but it's the easiest that I can think of. — chimeracoder
– chimeracoder, Commented Jul 10, 2011 at 21:13

Community · Accepted Answer · 2020-06-20 09:12:55Z

6

Yes, there is a way. From Django docs:

Field.default

The default value for the field. This can be a value or a callable object. If callable it will be called every time a new object is created.

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Jul 10, 2011 at 21:13

shanyu

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2 Comments

chimeracoder Over a year ago

Thanks! I didn't realize that default values could be callable functions.

Daniel Roseman Over a year ago

The trick is to make sure you assign the function as the default, not the result - so (eg) default=datetime.datetime.now rather than default=datetime.datetime.now().

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