使用JOIN访问现有数据库的表

Question

我在MySQL中有一个现有数据库，其中包含many-to-many关系表：

1. location
2. channel
3. location_channel - JOIN表。

我创建了模型：

class Location < ActiveRecord::Base
    self.table_name = "location"
    has_and_belongs_to_many :channels
end

class Channel < ActiveRecord::Base
    self.table_name = "channel"
    has_and_belongs_to_many :locations
end

在rails控制台中，我能够分别访问每个表的记录，例如：Location.all和Channel.all，

但是当我尝试通过以下方式访问给定channels的所有location时

location = Location.first
location.channels

这是错误的：

Mysql2::Error: Table 'mydb.channel_location' doesn't exist: SHOW FULL FIELDS FROM `channel_location`
ActiveRecord::StatementInvalid: Mysql2::Error: Table 'switchboard_2_api_poc.channel_location' doesn't exist: SHOW FULL FIELDS FROM `channel_location`

或者：

Mysql2::Error: Table 'mydb.channel_location' doesn't exist: SHOW FULL FIELDS FROM `channel_location`
ActiveRecord::StatementInvalid: Mysql2::Error: Table 'switchboard_2_api_poc.channel_location' doesn't exist: SHOW FULL FIELDS FROM `channel_location`

当我在尝试时：

channel = Channel.first
channel.locations

我怀疑，我需要以某种方式描述<{strong> JOIN表location_channel以消除错误并打印正确的值。

Answer 1

你需要告诉rails连接表的名称， 因为它错误地猜到了。

has_and_belongs_to_many :locations, join_table: 'location_channel'

http://apidock.com/rails/ActiveRecord/Associations/ClassMethods/has_and_belongs_to_many