ruby-on-rails - Rails 3 - has_and_belongs_to_many

Question

我有 2 个模型 - Teacher 和 Subject。 A 想通过名称为 Qualification 的 Join 表将它们连接起来。

看来我做错了什么:

class Teacher < ActiveRecord::Base
  has_and_belongs_to_many :subjects, :join_table => "Qualification"
end

class Subject < ActiveRecord::Base 
  has_and_belongs_to_many :teachers, :join_table => "Qualification"
end

我的迁移:

class CreateQualificationJoinTable < ActiveRecord::Migration
  def change
    create_table :qualification, :id => false do |t|
      t.integer :subject_id
      t.integer :teacher_id
    end
    add_index :qualification, :subject_id
    add_index :qualification, :teacher_id
  end
end

例如，当我打开 Rails 控制台并打印时

ruby-1.9.3-head :013 > Qualification

我明白了:

NameError: uninitialized constant Qualification
    from (irb):13
    from /Users/serg/.rvm/gems/ruby-1.9.3-head/gems/railties-3.2.0/lib/rails/commands/console.rb:47:in `start'
    from /Users/serg/.rvm/gems/ruby-1.9.3-head/gems/railties-3.2.0/lib/rails/commands/console.rb:8:in `start'
    from /Users/serg/.rvm/gems/ruby-1.9.3-head/gems/railties-3.2.0/lib/rails/commands.rb:41:in `<top (required)>'
    from script/rails:6:in `require'
    from script/rails:6:in `<main>'

怎么了？

Answer 1

首先，在迁移中创建表并没有定义您的模型。您必须在 app/models/qualification.rb 中创建一个 Qualification 模型:

class Qualification < ActiveRecord::Base
  belongs_to :subjects
  belongs_to :teachers
end

其次，如果您使用的是 Rails 3，请放弃 has_and_belongs_to_many 并使用 has_many :through:

class Teacher < ActiveRecord::Base
  has_many :qualifications
  has_many :subjects, :through => :qualifications
end

class Subject < ActiveRecord::Base 
  has_many :qualifications
  has_many :teachers, :through => :qualifications
end