crossing borders of tables: language role - ruby-on-rails

Question

I'm new to development, and have spent the last 12 hours (literally) trying to figure out this error message - I'm giving up for the night, but not before a quick cry for help to stackoverflow.
I have this form:
<h2>Select from the language options below (or, <%= button_to "Login", 'users/login', method: :get %></h2>
<%= form_for #language_role do |f| %>
<div id="input">
<h3>I want to learn:</h3><%= select_tag(:language_id, options_from_collection_for_select(Language.all, :id, :lang_name)) %>
</div>
<div>
<p><%= f.submit "Start learning" %></p>
</div>
<% end %>
which is giving me this error message, highlighting the line #language_role = current_user.language_roles.build : "undefined method `language_roles' for nil:NilClass"
I have three tables:
create_table "language_roles", force: :cascade do |t|
t.integer "language_id"
t.boolean "is_active"
t.boolean "is_teacher"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.integer "user_id"
t.index ["user_id"], name: "index_language_roles_on_user_id"
end
create_table "languages", force: :cascade do |t|
t.string "lang_name"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
create_table "users", force: :cascade do |t|
t.string "email", default: "", null: false
t.string "encrypted_password", default: "", null: false
t.string "reset_password_token"
t.datetime "reset_password_sent_at"
t.datetime "remember_created_at"
t.integer "sign_in_count", default: 0, null: false
t.datetime "current_sign_in_at"
t.datetime "last_sign_in_at"
t.string "current_sign_in_ip"
t.string "last_sign_in_ip"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.index ["email"], name: "index_users_on_email", unique: true
t.index ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true
end
The language_roles table is meant to allow a user to have many languages, as well as many roles within that language. Here are my class definitions:
class LanguageRole < ApplicationRecord
belongs_to :languages
belongs_to :users
end
class Language < ApplicationRecord
has_many :language_roles
has_many :users, :through => :language_roles
end
class User < ApplicationRecord
has_many :language_roles
has_many :languages, :through => :language_roles
# Include default devise modules. Others available are:
# :confirmable, :lockable, :timeoutable and :omniauthable
devise :database_authenticatable, :registerable,
:recoverable, :rememberable, :trackable, :validatable
end
My root path goes to 'home#index', where the user is supposed to pick a language if current_user.language_roles is empty. As such, I put this code in my home controller and language_roles controller:
class HomeController < ApplicationController
def index
#language_role = current_user.language_roles.build
end
end
class LanguageRolesController < ApplicationController
def create
#language_role = current_user.language_roles.build(language_role_params)
if #language_role.save
redirect_to root_path
else
redirect_to :back
end
end
private
def language_role_params
params.permit(:language_id)
end
end
What in the hell is the problem?? I assume I need to instantiate the variable somehow, but I'm not sure how.
Thanks,
Michael

Answer 1

There is a typo in your LanguageRole Model:
LanguageRole < ApplicationRecord
belongs_to :languages
belongs_to :users
end
should be
LanguageRole < ApplicationRecord
belongs_to :language
belongs_to :user
end
belongs_to associations must use the singular term.
The name of the other model is pluralized when declaring a has_many association.
Ref: http://guides.rubyonrails.org/association_basics.html

Answer 2

Your current_user is not defines it seems. You can install a gem called 'pry-rails' and debug your way out of this situation and any other in future. Here's a tutorial how to use it Railscasts #280

Answer 3

In your LanguageRole model you defined like belongs_to :users. But it should be belongs_to :user.
Your model look like ...
LanguageRole < ApplicationRecord
belongs_to :languages
belongs_to :users
end
Which should be something like
LanguageRole < ApplicationRecord
belongs_to :language
belongs_to :user
end