请教has_and_belongs_to_many保存

class ProductsCategory < ActiveRecord::Base
  has_and_belongs_to_many :products

class Product < ActiveRecord::Base
  has_and_belongs_to_many :products_categories
end

 def create
    @product = Product.new(params[:product])
    @product.products_categories = ProductsCategory.find(params[:category]["category_id"])
    if @product.save
      flash[:notice] = 'Product was successfully created.'
      redirect_to :action => 'list'
    else
      render :action => 'new'
    end
  end

 NoMethodError in A productController#create

undefined method `each' for #<ProductsCategory:0xb74bd464>

RAILS_ROOT: script/../config/..
Application Trace | Framework Trace | Full Trace

/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/base.rb:1860:in `method_missing'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/associations/association_collection.rb:137:in `replace'
/usr/local/lib/ruby/gems/1.8/gems/activerecord-1.15.3/lib/active_record/associations.rb:950:in `products_categories='
app/controllers/a_product_controller.rb:28:in `create'
/usr/local/bin/rdebug-ide:16:in `load'
/usr/local/bin/rdebug-ide:16

谢谢了， @product.products_categories = ProductsCategory.find(params[:category]["category_id"])哪里有问题？

不好意思，知道了原来要 <<
能删就删掉把

你好 。向你请教个问题。你的表结构是怎样的，你这两个表之间还有一个维护这两个表id的表吗

最好把表结构公开看一下。

按照"圣经"的说法,多对多的表需要第三张表来记录之间的关系.

habtm 肯定是需要一张中间表来维护id的。