这个 has_many through: 关联在哪里出错了？

Question

期望的结果：

Item.first.ratings 给了我该项目的评级。

所需的表和列：

item
  id,name,created_at,updated_at
ratings
  id,name,created_at,updated_at
item_ratings
  id,item_id,rating_id,value,created_at,updated_at

评分迁移：

class CreateRatings < ActiveRecord::Migration[5.0]
  def change
    create_table :ratings do |t|
      t.string :name
      t.references :user, foreign_key: true

      t.timestamps
    end
  end
end

加入表迁移：

class CreateJoinTableItemsRatings < ActiveRecord::Migration[5.0]
  def change
    create_join_table :items, :ratings do |t|
      t.index [:item_id, :rating_id]
      t.index [:rating_id, :item_id]
      t.string :value
    end
  end
end

商品型号：

class Item < ApplicationRecord
   belongs_to :user
   has_many :item_ratings
   has_many :ratings, through: :item_ratings
end

评级模型：

class Rating < ApplicationRecord
  belongs_to :user
  has_many :item_ratings
  has_many :items, through: :item_ratings
end

item_rating 模型：

class ItemRating < ApplicationRecord
  belongs_to :item
  belongs_to :rating
end

1. rails console
2. Item.first.ratings

结果：

Item Load (0.7ms)  SELECT  "items".* FROM "items" ORDER BY "items"."created_at" DESC LIMIT $1  [["LIMIT", 1]]   
ActiveRecord::StatementInvalid: PG::UndefinedTable: ERROR:  relation "item_ratings" does not exist
    LINE 8:                WHERE a.attrelid = '"item_ratings"'::regclass
                                              ^
    :               SELECT a.attname, format_type(a.atttypid, a.atttypmod),
                         pg_get_expr(d.adbin, d.adrelid), a.attnotnull, a.atttypid, a.atttypmod,
                 (SELECT c.collname FROM pg_collation c, pg_type t
                   WHERE c.oid = a.attcollation AND t.oid = a.atttypid AND a.attcollation <> t.typcollation),
                         col_description(a.attrelid, a.attnum) AS comment
                    FROM pg_attribute a LEFT JOIN pg_attrdef d
                      ON a.attrelid = d.adrelid AND a.attnum = d.adnum
                   WHERE a.attrelid = '"item_ratings"'::regclass
                     AND a.attnum > 0 AND NOT a.attisdropped
                   ORDER BY a.attnum

问题： 这个 has_many through: 关联在哪里出错了？这是正确的问题吗？

Answer 1

表item_ratings 不存在，但items_ratings 存在，尝试将所有出现的item_ratings 重命名为items_ratings。