如何在rails中使用4个表的连接查询

我有以下表4模型

class ItemCode < ActiveRecord::Base belongs_to :item_point end class ItemPoint < ActiveRecord::Base belongs_to :item has_many :item_codes end class Item < ActiveRecord::Base belongs_to :prodcut_category has_many :item_points end class ProductCategory < ActiveRecord::Base has_many :items end 

现在我必须使用product_category找到item_codes详细信息，因为我使用了内连接。 这是mysql查询

 SELECT * FROM `item_codes` utc INNER JOIN item_points rtp ON rtp.id = utc.item_point_id INNER JOIN items ri ON ri.id = rtp.item_id INNER JOIN product_catagories rpc ON rpc.id = ri.product_catagory_id WHERE rpc.id =1 LIMIT 0 , 30 

现在我必须以Acitve记录格式编写相同的查询。

 ItemCode.joins(:item_point).joins(:item).joins(:product_catagory).where("product_catagories.id = 1") 

得到以下错误

 ActiveRecord::ConfigurationError: Association named 'item_points' was not found; perhaps you misspelled it? 

那么如何以Active记录格式编写给定查询。

编辑

product_catagories

 +----------------------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +----------------------+--------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | client_id | int(11) | YES | | NULL | | | category_name | varchar(255) | YES | | NULL | | | category_description | varchar(255) | YES | | NULL | | | created_at | datetime | NO | | NULL | | | updated_at | datetime | NO | | NULL | | | scheme_id | int(11) | YES | MUL | NULL | | +----------------------+--------------+------+-----+---------+----------------+ 

item_points

 +----------------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +----------------+--------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | item_id | int(11) | YES | MUL | NULL | | | created_at | datetime | NO | | NULL | | | updated_at | datetime | NO | | NULL | | +----------------+--------------+------+-----+---------+----------------+ 

项目

+ —————————- + ————– + —– – + —– + ——— + ————

 ----+ | Field | Type | Null | Key | Default | Extra | +----------------------------+--------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | created_at | datetime | NO | | NULL | | | updated_at | datetime | NO | | NULL | | | product_catagory_id | int(11) | YES | MUL | NULL | | +----------------------------+--------------+------+-----+---------+----------------+ 

item_codes

 +----------------------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +----------------------+--------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | item_point_id | int(11) | YES | MUL | NULL | | +----------------------+--------------+------+-----+---------+----------------+ 

Answer 1

试试这个：

 ItemCode.joins(item_point: {item: :product_category}).where(product_category: {id: 1}) 

让我简化连接表 ：

当你有直接关系时 ：

 # item_code belongs_to item_point ItemCode.joins(:item_point) # ItemPoint has_many item_codes & belongs_to item ItemPoint.joins(:item_codes, :item) 

当您有间接/嵌套关系时 ：

 # ItemCode belongs_to item_point, item_point belongs_to item ItemCode.joins(item_point: :item) # ItemCode belongs_to item_point, item_point belongs_to item, item belongs_to product_category ItemCode.joins(item_point: {item: :product_category}) 

Answer 2

试试这个

 UniqueItemCode.joins(item_points: [{ items: :product_catagories }]).where(product_catagory: {id: 1})