activerecord - Rails 5: STI With Has Many Through Association -

i have searched extensively solution situation, can't find anything.

in application have person model only stores data people:

class person < applicationrecord end 

then have trial model. trials can have many people using has-many-through association. additionally, in context of trial, person can defendant or plaintiff. achieve this, set models this:

class trial < applicationrecord   has_many :trial_people   has_many :plaintiffs, class_name: 'plaintiff', through: :trial_people, source: :person   has_many :defendants, class_name: 'defendant', through: :trial_people, source: :person end  class trialperson < applicationrecord   belongs_to :trial   belongs_to :person end  class plaintiff < person end  class defendant < person end 

i using select2 jquery plugin add in defendants , plaintiffs each trial in view. obtaining ids in strong parameters:

params.require(:trial).permit(:title, :description, :start_date, :plaintiff_ids => [], :defendant_ids => []) 

so can achieve following:

trial.defendants trial.plaintiffs 

the problem not have way of distinguishing between classes inside trial_people table. thinking on adding type column table (sti), not know how automatically add type each defendant or plaintiff when saving trial object.

would appreciate insight on how achieve this, using sti or not.

one way can go without changing associations or schema use before_create callback.

assuming you've added person_type string column trial_people

class trialperson < applicationrecord   belongs_to :trial   belongs_to :person   before_create :set_person_type    private    def set_person_type     self.person_type = person.type   end end 

another way approach remove person association , replace polymorphic triable association. achieves same end result it's built activerecord api , doesn't require callbacks or custom logic.

# migration  class addtriablereferencetotrialpeople < activerecord::migration   def     remove_reference :trial_people, :person, index: true     add_reference :trial_people, :triable, polymorphic: true   end    def down     add_reference :trial_people, :person, index: true     remove_reference :trial_people, :triable, polymorphic: true   end end  # models  class trialperson < applicationrecord   belongs_to :trial   belongs_to :triable, polymorphic: true end  class person < applicationrecord   has_many :trial_people, as: :triable end  class trial < applicationrecord   has_many :trial_people   has_many :defendants, source: :triable, source_type: 'defendant', through: :trial_people   has_many :plaintiffs, source: :triable, source_type: 'plaintiff', through: :trial_people end  class plaintiff < person end  class defendant < person end 

this gives triable_type , triable_id columns on trial_people table set automatically when add collections

trial = trial.create trial.defendants << defendant.first trial.trial_people.first # => #<trialperson id: 1, trial_id: 1, triable_type: "defendant", triable_id: 1, ... >