Question

I am trying to create an association between two tables. A student table and a computer table.
A computer can only ever be assigned to one student (at any one time) but a student can be assigned to multiple computers.

This is what I currently have in mind. Setting up a has-many through relationship and modifying it a bit.

class Student < ActiveRecord::Base
  has_many :assignemnts
  has_many :computers, :through => :assignments
end

class Computer < ActiveRecord::Base
 has_one :assignment
 has_one :student, :through => :assignments
end

class Assignment < ActiveRecord::Base
  belongs_to :student
  belongs_to :computer
end

Does this seem like the best way to handle this problem? Or something better sound out quickly to the experts here. Thanks!

Answer 1

You need first to decide if a simple one-to many relationship is enough for you.

If yes, it gets a lot easier, because you can get rid of the Assignment-class and table.

Your database-table “computers” then needs a student_id column, with a non-unique index

Your models should look like this:

class Computer < ActiveRecord::Base
    belongs_to :student
end

class Student < ActiveRecord::Base
    has_many :computers, :dependent => :nullify
end

“dependent nullify” because you don’t want to delete a computer when a student is deleted, but instead mark it as free.

Each of your computers can only be assigned to a single student, but you can reassign it to a different student, for example in the next year.