RE: How to add an element of derived data to a Django model?

I apologize for adding noise to the thread. I didn't read this thread
before replying. Nkryptic is correct.

Sent from my Windows Phone

-----Original Message-----
From: nkryptic
Sent: 1/5/2013 11:59 PM
To: django-users@googlegroups.com
Cc: Saqib Ali
Subject: Re: How to add an element of derived data to a Django model?

Don't add it to the fields for the ModelAdmin, add it to the 'list_display':




class myModelAdmin(admin.ModelAdmin):

list_display = ('a', 'b', 'c')




On Saturday, January 5, 2013 4:25:11 PM UTC-5, Saqib Ali wrote:




I tried Aaron's method. Django validated the model.

However, when I added property "c" to the administration interface's
list of fields, It threw an error:




'myModelAdmin.fields' refers to field 'status' that is missing from the form.


Request Method:

GET



Request URL:

http://VVV/admin/



Django Version:

1.4.3



Exception Type:

ImproperlyConfigured



Exception Value:

'myModelAdmin.fields' refers to field 'status' that is missing from the form.


Exception Location:

/usr/lib/python2.6/site-packages/django/contrib/admin/validation.py in
check_formfield, line 396



Python Executable:

/usr/bin/python



Python Version:

2.6.8



Python Path:

['/WWW/XXX/YYY/ZZZ',
'/usr/lib/python26.zip',
'/usr/lib/python2.6',
'/usr/lib/python2.6/plat-linux2',
'/usr/lib/python2.6/lib-tk',
'/usr/lib/python2.6/lib-old',
'/usr/lib/python2.6/lib-dynload',
'/usr/lib/python2.6/site-packages',
'/usr/lib/python2.6/site-packages/setuptools-0.6c11-py2.6.egg-info']


Server time:

Sat, 5 Jan 2013 16:17:42 -0500






On Saturday, January 5, 2013 12:16:30 PM UTC-5, Tundebabzy wrote:
I think you can write a function that returns a > b and then make it a
getter method with python's property.

i would have given an example but typing code from my phone isn't very
appealing.

Sent from my Windows Phone

-----Original Message-----
From: Saqib Ali
Sent: 1/5/2013 5:50 PM
To: django...@googlegroups.com
Subject: How to add an element of derived data to a Django model?




I have a Django Model as follows:





class myModel(models.Model):


a = models.IntegerField()


b = models.IntegerField()




I want to add a models.BooleanField() named c to the myModel class.
However the value of c is simply derived from a and b so I don't want
it to be stored in the Database.

I want to c to be True if a > b, otherwise False. I want c to reflect
the correct/current value even when a and b get modifed. And I want to
be able to access c using myModel.c just like I can access a and b.




Is there any way to do this?

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