Question

I’m struggling to model a particular relationship with ActiveRecord. I currently have the following setup and working

class Schedule < ActiveRecord::Base
    has_many :tasks
end

class Task < ActiveRecord:Base
    belongs_to :schedule
end

with a database structure that looks like this:

schedules
  - integer:id

tasks
  - integer:id
  - integer:schedule_id

What I’d like to be able to do is set one of the tasks to be the active task for a schedule by adding an “active_task_id” column to the Schedules table:

schedules
  - integer:id
  - integer:active_task_id

tasks
  - integer:id
  - integer:schedule_id

What I’m struggling with is how I should describe this within my ActiveRecord classes

Answer 1

should look like this

class Schedule < ActiveRecord::Base 
    has_many :tasks 
    belongs_to :active_task, 
               :class_name => 'Task', 
               :foreign_key => 'active_task_id'
end 

class Task < ActiveRecord:Base 
    belongs_to :schedule 
    has_one :relevant_schedule,
            :class_name => 'Schedule',
            :foreign_key => 'active_task_id'
end 

the conceptually tricky part is defining the ‘relevant_schedule’ relation. this isn’t really needed in most cases (i.e. will not be used by code you write), is needed for compelteness of the ORM.

it’s unlikely you’ll ever want to use task.relevant_schedule (in many cases it would be nil), you’ll probably mostly want to use schedule.active_task in your code.

‘relevant_schedule’ is just an arbitrary name, you may choose any other name you like.
:class_name and :foreign_key must exactly match database and model names. perhaps the ‘relevant_schedule’ definition may be omitted altogether. i’m not sure.