Create join model record with accepts_nested_attributes_for

Question

I have following models

class User < ActiveRecord::Base
   has_many :project_users, dependent: :destroy
   has_many :projects, through: :project_users
end

class ProjectUser < ActiveRecord::Base
   belongs_to :user
   belongs_to :project
   has_many :participants
   has_many :tasks, through: :participants
end

class Task < ActiveRecord::Base
   belongs_to :project
   has_many :participants
   has_many :project_users, through: :participants
   accepts_nested_attributes_for :participants
end

class Participant < ActiveRecord::Base
   belongs_to :project_user
   belongs_to :task
 end

So the flow should go like this: 1. User creates the project 2. User adds users to project via the join model ProjectUser 3. User creates a task for the project and selects those users from ProjectUsers, who will participate in the task. So I put an accepts_nested_attributes_for method and tried to build the nested form.

In my controller:

 def new
    @task = Task.new
    @task.participants.build
 end

 def task_params
    params.require(:task).permit(:project_id, :project_phase_id, :priority_id, :title,     :due_date, :estimation, :responsible_id, :description, :participant_ids => [])#, :participants_attributes => [:project_user_id, :task_id])
 end

participants_attributes is commented

In my view:

= f.association :participants, as: :select

Actual HTML generated:

 <input name="task[participant_ids][]" type="hidden" value="">
 <select class="select optional form-control" id="task_participant_ids" multiple="multiple" name="task[participant_ids][]">
   <option value="57">AlexandeR MazeiN</option>
   <option value="59">Firenze</option>
   <option value="58">Vasily Strekotkin</option>
 </select>

I add options via ajax, value = ProjectUser.id I Have to do it like so, because I dont know which ProjectUsers there will be unless a concrete project for a task is selected.

Error I am getting:

Started POST "/tasks" for 127.0.0.1 at 2014-04-11 13:18:24 +0300
  User Load (0.7ms)  SELECT "users".* FROM "users" WHERE "users"."id" = 6 ORDER BY "users"."id" ASC LIMIT 1
Processing by TasksController#create as HTML
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"aXuk9ZuDvFZce+sbIQLRhWZlVjitMvySaJ7CwWfdmaQ=", "task"=>{"project_id"=>"20", "priority_id"=>"4", "project_phase_id"=>"40", "title"=>"Skepta", "due_date"=>"", "estimation"=>"8", "responsible_id"=>"6", "participant_ids"=>["", "57", "58"], "description"=>""}, "commit"=>"Create Task"}
  Team Load (0.4ms)  SELECT "teams".* FROM "teams" WHERE "teams"."id" = $1 LIMIT 1  [["id", 3]]
  Participant Load (0.5ms)  SELECT "participants".* FROM "participants" WHERE "participants"."id" IN (57, 58)
Completed 404 Not Found in 7ms

ActiveRecord::RecordNotFound - Couldn't find all Participants with IDs (57, 58) (found 0 results, but was looking for 2): 

Answer 1

Your param hash has the IDs from ProjectUser as participant_ids, so when it queries the database it is looking for Participant models with these IDs. You need to set these as project_user_id inside of a list of participants, something like this:

participants: [ { project_user_id: 57 }, { project_user_id: 58 } ]

I'm not super familiar with build, but something along these lines should allow AR to properly construct the associations.