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Ruby on Rails:has_many self-join

has-many has-many-through ruby-on-rails-5 rails-activerecord ruby

ThriceGood · 技术社区 · 7 年前

轨道5。

https://medium.com/@jbmilgrom/active-record-many-to-many-self-join-table-e0992c27c1e (最后一块:Has|manySelf连接表)

我试图在用户之间建立“代表性”关系。

基于上面链接中的教程,我编写了如下用户模型:

class User < ApplicationRecord
  has_many :representatives, through: :representive_link, source: :representative
  has_many :representive_link, foreign_key: :represented_user_id, class_name: 'representatives'

  has_many :represented, through: :represented_link, source: :represented
  has_many :represented_link, foreign_key: :representative_user_id, class_name: 'representatives'
end

class Representatives < ActiveRecord::Base
  belongs_to :representative, foreign_key: 'representative_user_id', class_name: 'User'
  belongs_to :represented, foreign_key: 'represented_user_id', class_name: 'User'
end

我还在数据库中创建了一个代表表,如下所示:

+----------------------+------------+------+-----+---------+----------------+
| Field                | Type       | Null | Key | Default | Extra          |
+----------------------+------------+------+-----+---------+----------------+
| id                   | bigint(20) | NO   | PRI | NULL    | auto_increment |
| representive_user_id | bigint(20) | YES  | MUL | NULL    |                |
| represented_user_id  | bigint(20) | YES  | MUL | NULL    |                |
| created_at           | datetime   | NO   |     | NULL    |                |
| updated_at           | datetime   | NO   |     | NULL    |                |
+----------------------+------------+------+-----+---------+----------------+

因此,在Rails控制台中,我创建了两个用户:

u1 = User.create('id' => 1, 'username' => 'john')
u2 = User.create('id' => 2, 'username' => 'mike')

我希望u2代表u1:

u1.representatives = [u2]

NameError: uninitialized constant User::representatives

我发现这个概念很混乱,这里的其他帖子并没有为我澄清。有人能就我的问题打破这个概念吗?

2 回复 | 直到 7 年前

ThriceGood 7 年前

好的,最后我对它进行了一些轻微的修改。首先,我重命名了一些东西,使其更有意义(如果只是在我的脑海中)。

用户模型:

class User < ApplicationRecord
  has_many :represented_link, foreign_key: :representative_id, class_name: 'RepresentativeGrouping'
  has_many :represented, through: :represented_link, source: :represented

  has_many :representive_link, foreign_key: :represented_id, class_name: 'RepresentativeGrouping'
  has_many :representatives, through: :representive_link, source: :representative
end

代表性组合模型:

class RepresentativeGrouping < ApplicationRecord
  belongs_to :representative, foreign_key: 'representative_id', class_name: 'User'
  belongs_to :represented, foreign_key: 'represented_id', class_name: 'User'
end

mysql> describe representative_groupings;
+-------------------+------------+------+-----+---------+----------------+
| Field             | Type       | Null | Key | Default | Extra          |
+-------------------+------------+------+-----+---------+----------------+
| id                | bigint(20) | NO   | PRI | NULL    | auto_increment |
| representative_id | bigint(20) | YES  | MUL | NULL    |                |
| represented_id    | bigint(20) | YES  | MUL | NULL    |                |
| created_at        | datetime   | NO   |     | NULL    |                |
| updated_at        | datetime   | NO   |     | NULL    |                |
+-------------------+------------+------+-----+---------+----------------+

这里至关重要的一点是用户模型中有许多定义的排列。在关于的问题中,您会看到其中包含through:和source:的has\u many定义位于下面,has\u many定义具有class\u name:和foreign\u key:。在我更改了周围的名称后,我通过了我的第一个错误:

NameError: uninitialized constant User::representatives

但接着又出现了另一个错误:

ActiveRecord::HasManyThroughOrderError: Cannot have a has_many :through association 'User#representatives' which goes through 'User#representive_link' before the through association is defined.

Google引导我来到这里: https://github.com/rails/rails/issues/29123

在这些更改之后,我能够运行以下代码:

u1 = User.create(:id => 1, :username => 'john')
u2 = User.create(:id => 2, :username => 'mike')

u1.representatives = [u2]
puts u1.representatives

### displays u2's data

puts u2.represented

### displays u1's data

Gaudam Thiyagarajan 7 年前

得到 - has_and_belongs_to_many :representatives, class_name: "User", join_table: : representative_groupings, foreign_key: :represented_id, association_foreign_key: : representative_id

得到 - has_and_belongs_to_many : represented, class_name: "User", join_table: : representative_groupings, foreign_key: :representative_id, association_foreign_key: : represented_id

这也消除了对显式模型的需要 -