如何从关联访问联接表属性（has_many：through）

Question

I'm trying to create records list with the attributes of the associated records. Get Task goal Attribute inherit \\ replace Power - goal Attribute

if we have:

@tasks = user.tasks

when we render the view

<%= render @tasks %>

Everything is fine, we can just use <%= task.goal %> in the partial and all working, but if we have user.super_tasks how to override goal in the partial?

The first thing that comes to mind is to make in the _task.htm.erbl

<%= goal = if @super_tasks then task.powers.find_by(user_id: current_user).goal else task.goal end %>

It's kind of make it, but this ok if you have 3 records, with 15 it will make 15 request to db to find the join table each time.

Just added the tables to make it more clear:

class User < ActiveRecord::Base
   has_many :tasks
   has_many :powers
   has_many :super_tasks , through: :powers, source: :task
end

class Task < ActiveRecord::Base
   belongs_to :user
   has_many :powers
end

class Power < ActiveRecord::Base
   belongs_to :user
   belongs_to :tasks 
end

But if user have power they have more responsibilities, its not the first time that I stuck on that problem, for sure there is other way to make this work without calling the db each time, as it sadly common problem.

Answer 1

Ok maybe it not the best solution, but it works and answers the question:

tasks = user.tasks.order(:id)
power_tasks = user.powers.order(:task_id)

tasks.each_with_index do |task,i|
    task.goal = power_tasks[i].goal 
end

The weak point if this code is, if we say there is no task_id to order \\ adjust the power or if the number power_tasks does not match the tasks. But for my case it worked perfectly.

If you want to added other param, that not exist on normal Task , but exist on Power table and you want to added it to tasks also, then in the model we can:

class Task < ActiveRecord::Base
   attr_accessor :cookies

task.cookies = power_tasks[i].cookies