Question

I’m in the process of trying to develop my first rails application and before I jump off into actually implementing my ideas, I was hoping I could get some help with my association planning.

My application is going to be an educational tool and I have some basic functionality that I need to implement. I want to have students that can register for and create courses. Within these courses, there will be one user who is the teacher and the rest are students. Within the course will be assignments that the teacher creates and that users are required to make a submission for. These are the basics. Eventually I want to add more functionality but as of now I just need the foundations set.

Here are my ideas so far on what the associations should look like:

class User < ActiveRecord::Base
    has_many :enrollments
    has_many :courses, :through => :enrollments
end

class Course < ActiveRecord::Base
    has_many :enrollments
    has_many :users, :through => :enrollments
end

class Enrollment < ActiveRecord::Base
    belongs_to :user     # foreign key - user_id
    belongs_to :course   # foreign key - course_id
end

However, I’m running into my wall of inexperience at the moment with how to appropriately handle the rest of the associations at this point. I could probably hack out something, but I’d prefer to do it as best as I can the first time.

How do I handle the associations related to assignments and submissions? Presumably a student’s submission should belong_to them, but it is also specifically related to an assignment within the class. Assignments originate within a course, but are also closely tied to the user.

Finally, what’s the best way to handle the relationships between a user and the class they create? A user creates a course. Does that course belong_to them? Should I just add a column to the course’s table for storing the creator’s id? Etc.

Thanks for the help.

Answer 1

Suggestion:
You might want to separate out your Teacher and Student models, since you’re very likely to have different actions associated with each (and while they share some attributes, they really are different entities in your model, for example, you likely want just one teacher teaching in a course.)
You could derive both the Teacher model and the Student model from a User model that has the shared attributes and authentication.

Now to your questions:

If you’d like to keep the student that created the course associated, creator_id is the way I’d go. (If a teacher can create a course too, deriving Student and Teacher from a shared User model would help)

Assignments and Submissions:
You’ve pretty much defined it in words. Here is the code.
[If different students within a course could get different assignments, only then do you want to build a direct association between Student and Assignment, otherwise, use a through association]

class User < ActiveRecord::Base
    has_many :enrollments
    has_many :courses, :through => :enrollments
    has_many :assignments, :through => :courses
    has_many :submissions
end

class Course < ActiveRecord::Base
    has_many :enrollments
    has_many :users, :through => :enrollments
    has_many :assignments
end

class Enrollment < ActiveRecord::Base
    belongs_to :user     # foreign key - user_id
    belongs_to :course   # foreign key - course_id
end

class Assignment < ActiveRecord::Base
    belongs_to :course
    has_many :submissions
end

class Submission < ActiveRecord::Base
    belongs_to :assignment
    belongs_to :user
end