django 'DateTimeField' has no default value error

Question

i am novice at django development. i am creating a class A which might have multiple class B assigned to it:

class A(models.Model):        
    name = models.CharField(max_length=200)    

    def __unicode__(self):
        self.name


class B(models.Model):
    a = models.ForeignKey(A)
    name = models.CharField(max_length=200)
    mydate = models.DateTimeField('party date')

When i am trying to create a new "A" element at the admin page, and creating a matching element B for it and then save() , i am getting the Warning: Field 'mydate' doesn't have a default value

If i move the "mydate",element to class A, then when hitting save() i am getting a message This field is require from Django, requires me to fill the field!

how can i make this required message appear also when date field is part of B!!!

Thanks

Answer 1

If you have not specified, that your field is optional, you will have to provide a value for it every time you create an object. In your case you can't so you will have to do one of those things:

Here is how to make field optional:

class B(models.Model):
    a = models.ForeignKey(A)
    name = models.CharField(max_length=200)
    mydate = models.DateTimeField('party date', blank=True, null=True)

Here is how you set the default value:

import datetime

class B(models.Model):
    a = models.ForeignKey(A)
    name = models.CharField(max_length=200)
    mydate = models.DateTimeField('party date', default=datetime.datetime.now)

Answer 2

There's an utility function in Django

from django.utils import timezone
class B(models.Model):
  a = models.ForeignKey(A)
  name = models.CharField(max_length=200)
  mydate = models.DateTimeField('party date', default=timezone.now)

This function will return you a datetime object based on USE_TZ in settings.py

def now():
  """
  Returns an aware or naive datetime.datetime, depending on settings.USE_TZ.
  """
  if settings.USE_TZ:
      # timeit shows that datetime.now(tz=utc) is 24% slower
      return datetime.utcnow().replace(tzinfo=utc)
  else:
      return datetime.now()