How to hide model field in Django Admin? - django

Question

I generate field automaticly, so I want to hide it from user. I've tried editable = False and hide it from exclude = ('field',). All this things hide this field from me, but made it empty so I've got error: null value in column "date" violates not-null constraint.
models.py:
class Message(models.Model):
title = models.CharField(max_length = 100)
text = models.TextField()
date = models.DateTimeField(editable=False)
user = models.ForeignKey(User, null = True, blank = True)
main_category = models.ForeignKey(MainCategory)
sub_category = models.ForeignKey(SubCategory)
groups = models.ManyToManyField(Group)`
admin.py:
class MessageAdminForm(forms.ModelForm):
def __init__(self, *arg, **kwargs):
super(MessageAdminForm, self).__init__(*arg, **kwargs)
self.initial['date'] = datetime.now()
class MessageAdmin(admin.ModelAdmin):
form = MessageAdminForm
list_display = ('title','user',)
list_filter = ('date',)

Answer 1

Based on your model setup, I think the easiest thing to do would change your date field to:
date = models.DateTimeField(auto_now=True)
that should accomplish what you're after and you don't even need to exclude it from the admin, it's excluded by default. If you have auto_now=True it will act as a 'last update time'. If you have auto_now_add=True it will act as a creation time stamp.
There are several other ways you could accomplish your goal if your use case is more complex than a simple auto date field.
Override the model's save method to put the value in.
class Message(models.Model):
title=models.CharField(max_length=100)
date = models.DateTimeField(editable=False)
def save(*args, **kwargs):
self.date = datetime.datetime.now()
super(Message, self).save(*args, **kwargs)
What you are trying to do with the Model Admin isn't quite working because by default django only transfers the form fields back to a model instance if the fields are included. I think this might be so the model form doesn't try to assign arbitrary attributes to the model. The correct way to accomplish this would be to set the value on the instance in your form's save method.
class MessageAdminForm(forms.ModelForm):
def save(*args, **kwargs):
self.instance.date = datetime.now()
return super(MessageAdminForm, self).save(*args, **kwargs)