Re: Problem with CircularDependency Model

Thank you very much for the great answer!
You are correct, I didn't had a clear understanding of the RelatedObject Principle. I think I added this when I was fiddling with the rest framework.
Of course, I also had thought about making MasterUser a boolean, but I need to ensure that there is only one MasterUser. I thought about doing it in the Code, but I thought it might be better to enforce it at Database Level. However, I think your solution is much better.
I also thought having a separate Table for the MasterUser Relationship, like you suggested. I tried to some find some suggestions on how to model a relationship like that. I think, I will go for the boolean field but my intuitive assumption would be to overwrite the pre_save method. post_save kinda sounds like it is too late at that point.

Anyway, thanks a lot for you recommendations!

On Friday, May 19, 2017 at 5:50:42 PM UTC+2, Melvyn Sopacua wrote:

 

Yep, let me see if I got it right:

- The User model is defined as AUTH_USER_MODEL in settings.py

- User points to institute

- Institute points to User

 

So it is in fact a circular dependency on the model level as well. And one you don't need.

 

From the way you defined the related_name it is also clear you don't get the RelatedObject principle of Django.

 

A ForeignKey creates a bridge between two models: you can travel in both directions. Using your models:

 

class User(AbstractBaseUser, PermissionsMixin):

username = ...

 

class Institute(models.Model):

master_user = models.ForeignKey(settings.AUTH_USER_MODEL, related_name='institute')

members = models.ManyToManyField(settings.AUTH_USER_MODEL)

 

Because of the ForeignKey on Institute, Django creates an attribute on User, called 'institute'. It uses institute, because I specified that as related_name. You could use a different name there, but it has to be a name that can be used on the model you point to.

 

However, this isn't a good representation of realitity, given your own description.

So this is a better way to do it:

 

class User(AbstractBaseUser, PermissionsMixin):

institute = models.ForeignKey('port.Institute', related_name='members')

is_master_user = models.BooleanField(default=False)

 

class Institute(models.Model)

name = models.CharField(max_length=255)

# members is now created by the foreign key

@property

def master_user(self):

return self.members.get(is_master_user=True)

 

This model is much simpler. All you need to do is to verify that when someone is made master user, that all other members of the institute are *not* master user.

 

You can do this in a post_save signal or in the clean method of User , both with its own caveats.

 

Another way would be to define a MasterUser model, which is easier to maintain in the admin:

 

class MasterUser(models.Model):

# Assume one person can be master user of many institutes

# if not, this also has to be a OneToOneFIeld

user = models.ForeignKey(settings.AUTH_USER_MODEL)

institute = models.OneToOneField(Institute, related_name='master_user')

--

Melvyn Sopacua

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