为什么我会在轨道4连接表一个未知的主键异常？ [英] Why do I get an Unknown Primary Key exception for a join table in Rails 4?

问题描述

这些都是我的模型：

class Product
  has_many :line_items
  has_many :orders, :through => :line_items
end

class LineItem 
  belongs_to :order
  belongs_to :product
end

class Order
    has_many :line_items
    has_many :products, :through => :line_items
end

从schema.rb：

From schema.rb:

  create_table "line_items", id: false, force: true do |t|
    t.integer  "order_id"
    t.integer  "product_id"
    t.integer  "quantity"
    t.datetime "created_at"
    t.datetime "updated_at"
  end

我刚刚升级到Rails的4，我的连接表停止工作。如果我做 @ order.line_items ，它会抛出异常未知主键模型LINEITEM表line_items。 <$ C C $> @ order.products 按预期工作。

I just upgraded to Rails 4, and my join table stopped working. If I do @order.line_items, it throws the exception "Unknown primary key for table line_items in model LineItem." @order.products works as expected.

我试图删除和重建line_items表，我试图安装protected_attributes宝石，但什么都没有改变。

I have tried dropping and recreating the line_items table, and I have tried installing the protected_attributes gem, but nothing changed.

下面是跟踪。

推荐答案

在模型中加入

self.primary_key = [:order_id, :product_id]

，我认为这将是明智的，以确保有对这些列的索引。您可以创建具有以下迁移一个

and I think it would be wise to ensure that there's an index on those columns. You may create one with following migration

add_index :line_items, [:order_id, :product_id]

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