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Django: structuring a complex relationship intended for use with built-in admin site

Posted on 2009-12-23
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Last Modified: 2012-06-27


Hi,

I have a fairly complex relationship that I am trying to make work with the Django admin site. I have spent quite some time trying to get this right and it just seems like I am not getting the philosophy behind the Django models.

There is a list of Groups. Each Group has multiple departments. There are also Employees. Each Employee belongs to a single group, but some employees also belong to a single Department within a Group. (Some employees might belong to only a Group but no Department, but no Employee will belong only to a Department).

Here is a simplified version of what I currently have:

class Group:
  name = models.CharField(max_length=128)

class Department
  group = models.ForeignKey(Group)

class Employee
  department = models.ForeignKey(Department)
  group = models.ForeignKey(Group)

The problem with this is that the Department select box on the Employees page must display all Departments, because a group has not yet been set. I tried to rectify this by making an EmployeeInline for the GroupAdmin page, but it is not good to have 500+ employees on a non-paginated inline. I must be able to use the models.ModelAdmin page for Employees (unless there is a way to search, sort, collapse and perform actions on inlines).

If I make EmployeeInline an inline of DepartmentAdmin (instead of having a DepartmentInline in GroupAdmin), then things are even worse, because it is not possible to have an Employee that does not belong to a Group.

Given my description of the relationships, am I missing out on some part of the Django ORM that will allow me to structure this relationship the way it 'should be' instead of hacking around and trying to make things come together?

Thanks a lot.
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Question by:RockyMountains
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Kevin Cross earned 2000 total points
ID: 26120264
RockyMountains,

(I am not good with Python or Django ORM to be clear)

Nothing too glaringly wrong the database relationship, IMHO, as you may someday change the business rule that an Employee can belong to a department and not a group.

With that said, though, since your current business logic is 1 group and 0-1 department (but only if a group membership exists), then I would handle this on the presentation (user interface) side of things.  Instead of presenting a list of departments since group is not yet selected, select group first.  In other words make the group selection first, then on change show your department selection.  This would ensure that the department chosen is only in the group selected.  Also since you may have a group only, you eliminate the user confusion of having to look at departments that ultimately won't get selected at all.

I may be way off, but thought I would share the thought I had.

Otherwise, you can set a trigger / constraint on database to ensure that department is NULL unless group is NOT NULL.

--isa
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