Passing an instance variable from one controller to another in rails

Question

I have a rails application that has an admins model which has many users and users has_and_belongs_to_many materials. The problem is that for a specific user (for example user/show/2) I have a form on that page that posts to materials create action. In the create action here is what I am trying to do

def create
@material = @user.materials.create(material_params)
end

However, it won't work because @user is nil. This needs to associate a material with a user via the users_materials table (because of the has_and_belongs_to_many association). So, how would I define a material from a users page (user/show/:id) and be able to define a material for that user? What is a good way to do this in rails?

Can you show what your view code looks like for the post to materials? — lurker
– lurker, Commented Sep 9, 2013 at 16:26

MrTheWalrus · Accepted Answer · 2013-09-09 16:31:34Z

1

It sounds as though what you have is Nested Resources.

There's a RailsCast about them here, and they're discussed in this guide.

The quick version is that you're going to define your routes approximately like so:

resources :users do
  resources :materials
end

And that the form will POST to /users/:user_id/materials, which I believe you'd call as users_materials_path(@user).

The controller action (MaterialsController#create) will be able to refer to params[:user_id], and can either simply assign that as the user_id of the Material, or actually load that user (User.find(params[:user_id]) and then call .materials.create on it.

edited Sep 9, 2013 at 16:31

answered Sep 9, 2013 at 16:25

MrTheWalrus

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3 Comments

Brock90 Over a year ago

Thank you for the answer it worked.However something confuses me.Why params[:user_id] and not params [:id] ?

MrTheWalrus Over a year ago

It's how the nested resource pattern works. The reasoning behind it is consistency. For instance, to see a particular Material of a particular user, the path is /users/:user_id/materials/:id. In that case, params[:id] is the material id, so the user id needs a different name - hence user_id. It would be weird, though, if your show action referred to the user id as params[:user_id] but create called it params[:id], so it's just always user_id.

Brock90 Over a year ago

Ah I see now why I was confused I was thinking that maybe it had some kind of connection with the materials_users table(for the has_and_belongs_to_many relationship) which has a user_id.Thanks for clearing that up!

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