Question

I am developing a Rails application which uses a many-to-many relationship, which needs extra attributes on the join table (apart from the ids of the two related entities).

In the model, a Product can belong to many Orders, and an Order can have many Products.
So I created an action for assigning Products to a given Order, called add_product_order, and the controller method that handles the form when it’s sent is finish_add_product_order:

def finish_add_product_order
  @order = Order.find(params[:id])
  @product = Product.find(params[:order][:products])

  if @op = OrdersProduct.find_by_order_id_and_product_id(@order.id, @product.id)
    @op.quantity = params['quantity'][0]
  else
    @op = OrdersProduct.new(:order => @order, :product => @product, :quantity => params['quantity'][0])
  end

  respond_to do |format|
    if @op.save
      format.html { redirect_to @order, notice: 'Order was successfully updated.' }
      format.json { head :no_content }
    else
      format.html { render action: "add_product_order", notice: 'No se ha podido grabar.' }
      format.json { render json: @order.errors, status: :unprocessable_entity }
    end
  end
end

The orders_products table (which is used for storing the related ids and quantities) has the following index:

add_index :orders_products, [:order_id, :product_id], :unique => true

The action above (finish_add_product_order) works fine if the Product isn’t already in the Order (i.e. OrdersProduct.new is being called). But this is the error I get when it already exists and I try to save it:

SQLite3::SQLException: no such column: orders_products.: UPDATE "orders_products" SET "quantity" = 4 WHERE "orders_products"."" IS NULL

The request parameters are the following, just in case:

{"utf8"=>"✓",
 "_method"=>"put",
 "authenticity_token"=>"TwPMk73MhCM2IeMfmf2g/fdm3+ahpyaxs1InULC/8ig=",
 "order"=>{"products"=>"4"},
 "quantity"=>["4"],
 "commit"=>"Update Order",
 "id"=>"2"}

I believe the WHERE clause should include both the order and the product id so as to identify the row affected, but I don’t know why the column names are not being included, neither why it ends with “IS NULL”.

Any suggestions? Thanks

EDIT

This is the code for the three classes involved:

class Order < ActiveRecord::Base
  belongs_to :user

  has_many :gardens, :dependent => :destroy

  has_many :products, :through => :orders_products
  has_many :orders_products

  attr_accessible :address, :delivery_date, :paid, :user, :orders_products_attributes

  # hid some irrelevant methods
end



class Product < ActiveRecord::Base
  has_many :gardens, :through => :gardens_products
  has_many :gardens_products

  has_many :orders, :through => :orders_products
  has_many :orders_products

  attr_accessible :cost, :description, :stock, :title, :x_size, :y_size, :pivot_x_position, :pivot_y_position, :is_gallery_product

  validates_presence_of :cost, :stock, :title, :x_size, :y_size, :pivot_x_position, :pivot_y_position
  validates_numericality_of :cost, :stock, :x_size, :y_size, :pivot_x_position, :pivot_y_position, :only_integer => true, :message => "Solo puede ser un numero entero"
  validates_inclusion_of :cost, :in => 0..1000000, :message => "Solo puede estar entre 0 y 1 000 000"
  validates_inclusion_of :stock, :in => 0..10000000, :message => "Solo puede estar entre 0 y 10 000 000"
  validates_inclusion_of :x_size, :y_size, :in => 1..200, :message => "Solo puede estar entre 0 y 200"
  # Poner el rango variable en los pivotes (dentro del rango del tamano)
  validates_inclusion_of :pivot_x_position, :in => 1..200, :message => "El pivote debe estar dentro de las dimensiones del producto"
  validates_inclusion_of :pivot_y_position, :in => 1..200, :message => "El pivote debe estar dentro de las dimensiones del producto"
  validates :title, :length => { :minimum => 5},
                            :presence => { :message => "Debe tener un titulo de largo mayor que 5 caracteres" }
end


class OrdersProduct < ActiveRecord::Base
  belongs_to :order, :dependent => :destroy
  belongs_to :product

  attr_accessible :order, :product, :quantity

  validates_numericality_of :quantity,
                            :only_integer => true,
                            :message => "solo puede ser un numero entero"
  validates_inclusion_of :quantity,
                            :in => 1..1000,
                            :message => "solo puede estar entre 1 y 1 000"
end

Thanks again

Answer 1

Since the orders_products table had been created without an id (with create_table :orders_products, :id => :false do |t|...), all I had to do was to add an id to it, with this migration:

class AddIdToOrdersProduct < ActiveRecord::Migration
  def change
    add_column :orders_products, :id, :primary_key
  end
end

that way, it worked after doing rake db:migrate.