Question

I’m banging my head against a Problem with AR Associations for 2 days now. I know there is a easy solution to this but I can’t figure out.

I have two models Products and Users, that should be linked together. A Product should belong to a user and a user should have many products. I didn’t manage to set the user variable in my controller, so I went for a habtm association. Here are the models:

User.rb

class User < ActiveRecord::Base
# Include default devise modules. Others available are:
#...

has_and_belongs_to_many :products

Product.rb

class Product < ActiveRecord::Base
has_many :product_images, :dependent => :destroy
accepts_nested_attributes_for :product_images, :allow_destroy => :true
has_and_belongs_to_many :users

products_controller.rb

class ProductsController < ApplicationController

def index
@products = Product.search(params[:search]).order(sort_column + ' ' + sort_direction).paginate(:per_page => 10, :page => params[:page])

respond_to do |format|
  format.html # index.html.erb
  format.json { render json: @products }
end
end

def new
@user = current_user
@product = Product.new#@user.products.build(params[:product])
@product.product_images.build
respond_to do |format|
  format.html # new.html.erb
  format.json { render json: @product }
end
end

def create
@user = current_user
@product =  @user.products.build(params[:product])#Product.new(params[:product])
    @product.product_images.build
    @user.products << @product

respond_to do |format|
  if @product.save
    format.html { redirect_to @product, notice: 'Product was successfully created.' }
    format.json { render json: @product, status: :created, location: @product }
  else
    format.html { render action: "new" }
    format.json { render json: @product.errors, status: :unprocessable_entity }
  end
end
end

_form.html.erb

<%= form_for @product, :html => {:multipart => true, :class => 'form-horizontal'} do |f| %>

schema.rb

....
create_table "products_users", :id => false, :force => true do |t|
t.integer "product_id"
t.integer "user_id"
end
....

So, even I know, there should be a one-to-many association between user and product, this works out for me.
In IRB, I can do this:

u = User.first
u.products

with the habtm association I can even do it viseversa:

p = Product.first
p.users

But I can’t access the user attributes:

p.users.username:

NoMethodError:   User Load (2.0ms)  SELECT "users".* FROM "users" INNER JOIN "products_users" ON "users"."id" = "products_users"."user_id" WHERE "products_users"."product_id" = 12

Could anybody be so nice to help me out of this? What am I doing wrong?

Thanks a lot! Your help would save my weekend!

EDIT: Here’s my controller action for the one-to-many relation:

class ProductsController < ApplicationController

helper_method :sort_column, :sort_direction
def index
@products = Product.search(params[:search]).order(sort_column + ' ' + sort_direction).paginate(:per_page => 10, :page => params[:page])

respond_to do |format|
  format.html # index.html.erb
  format.json { render json: @products }
end

end

def show
@product = Product.find(params[:id])
@images = @product.product_images
respond_to do |format|
format.html # show.html.erb
format.json { render json: @product }
end
end

def new
@user = current_user
@product = Product.new#@user.products.build(params[:product])
@product.product_images.build
#3.times { @product.product_images.build }
respond_to do |format|
  format.html # new.html.erb
  format.json { render json: @product }
end
end


def edit
@product = Product.find(params[:id])
    @product.product_images.build
end


def create
@user = current_user
@product =  @user.products.build(params[:product])#Product.new(params[:product])
    @product.product_images.build


respond_to do |format|
  if @product.save
    format.html { redirect_to @product, notice: 'Product was successfully created.' }
    format.json { render json: @product, status: :created, location: @product }
  else
    format.html { render action: "new" }
    format.json { render json: @product.errors, status: :unprocessable_entity }
  end
end
end


def update
@product = Product.find(params[:id])

respond_to do |format|
  if @product.update_attributes(params[:product])
    format.html { redirect_to @product, notice: 'Product was successfully updated.' }
    format.json { head :no_content }
  else
    format.html { render action: "edit" }
    format.json { render json: @product.errors, status: :unprocessable_entity }
  end
end
end


def destroy
 @product = Product.find(params[:id])
 @product.destroy

respond_to do |format|
  format.html { redirect_to products_url }
  format.json { head :no_content }
end
end

private
def sort_column
Product.column_names.include?(params[:sort]) ? params[:sort] : "created_at"
# params[:sort] || "created_at"
end

def sort_direction
%w[asc desc].include?(params[:direction]) ? params[:direction] : "asc"
# params[:direction] || "asc"
end
end

EDIT2: Schema.rb

create_table "products", :force => true do |t|
t.string   "title"
t.string   "description"
t.string   "testimonial"
t.decimal  "credits",       :precision => 3, :scale => 0
t.datetime "created_at",                                  :null => false
t.datetime "updated_at",                                  :null => false
t.decimal  "age"
t.string   "condition"
t.string   "product_image"
t.string   "image"
t.integer  "user_id"
end

create_table "users", :force => true 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
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.string   "username"
t.integer  "product_id"
end

Answer 1

Don’t use a has_and_belongs_to_many if you have a one-to-many relation. Creating and maintaining another table is adding too much complexity. My advice would be to figure out why you can’t make the one-to-many relation working.

You should be able to make this work :

class User < ActiveRecord::Base
  has_many :products #Plural
end


class Product < ActiveRecord::Base
  belongs_to :user #Singular
end

If it doesn’t work, copy/paste your controller code that you use for one-to-many relation!

Good luck