Question

I have a simple userprofile class in django such that

class Profile(models.Model):
    user = models.OneToOneField(User,unique=True)
    gender = models.IntegerField(blank=True, default=0, choices=UserGender.USER_GENDER,db_column='usr_gender')
    education = models.IntegerField(blank=True, default=0, choices=UserEducation.USER_EDU,db_column='usr_education')
    mail_preference = models.IntegerField(blank=True, default=1, choices=UserMailPreference.USER_MAIL_PREF,db_column='usr_mail_preference')
    birthyear = models.IntegerField(blank=True, default=0,db_column='usr_birthyear')
    createdate = models.DateTimeField(default=datetime.datetime.now)
    updatedate = models.DateTimeField(default=datetime.datetime.now)
    deletedate = models.DateTimeField(blank=True,null=True)
    updatedBy = models.ForeignKey(User,unique=False,null=True, related_name='%(class)s_user_update')
    deleteBy = models.ForeignKey(User,unique=False,null=True, related_name='%(class)s_user_delete')
    activation_key = models.CharField(max_length=40)
    key_expires = models.DateTimeField()

You can see that deletedBy and updatedBy are foreign key fields to user class. If I don’t write related_name='%(class)s_user_update' it gives me error (I don’t know why).
Although this works without any error, it doesn’t push the user id’s of deletedBy and updatedBy fields although I assign proper user to them.

Could give me any idea and explain the related_name='%(class)s_user_update' part ?

Thanks

Answer 1

'%(class)s_user_update' implies that it is a string awaiting formatting. You would normally see it in the context:

'%(foo)s other' % {'foo': 'BARGH'} 

Which would become:

'BARGH other'

You can read more about python string formatting in the python docs. String Formatting Operations

I can’t see how the code you have would ever work: perhaps you want:

class Profile(models.Model):
    # other attributes here
    updated_by = models.ForeignKey('auth.User', null=True, related_name='profile_user_update')
    deleted_by = models.ForeignKey('auth.User', null=True, related_name='profile_user_deleted')
    # other attributes here

If it does work, it is because django is doing some fancy magic behind the scenes, and replacing '%(class)s' by the class name of the current class.

Notes on the above:

• The consistent use of *snake_case* for attributes. If you must use camelCase, then be consistent for all variables. Especially don’t mix *snake_case*, camelCase and runwordstogethersoyoucanttellwhereonestartsandtheotherends.
• Where you have two attributes that reference the same Foreign Key, you must tell the ORM which one is which for the reverse relation. It will default to ‘profile_set’ in this case for both, which will give you the validation error.
• Use ‘auth.User’ instead of importing User into the models.py file. It is one less import you’ll need to worry about, especially if you don’t use the User class anywhere in your models.py file.