Ruby on rails 如何通过Rails ActiveRecord中的连接正确地为has\u many添加别名？

这里是Rails/ActiveRecord新手。考虑以下模型：教室、用户和教室（两个连接）< /P>

课堂{where（duration:'full-time'）}，班级名称：“ClassroomEnrollments”
有许多：全职人员，：通过=>：全职人员注册，课程名称：“用户”
有很多：兼职登记，->{where（持续时间：'part-time'）}，班级名称：“ClassroomEnrollments”
有很多：兼职者，：通过=>：兼职注册，课程名称：“用户”
结束
类ClassroomEnrollment：教室注册
结束

教室和教室注册的以下模型不起作用。特别是

：fulltimers

和

：parttimers

别名在我试图通过

我的教室.fulltimers

或

我的教室.parttimers

访问它们时，为nil:NilClass抛出

未定义的方法'to_sym'

如果我删除
:parttimers
别名并将
:fulltimers
重命名为
:users
，它可以正常工作（并且只显示全日制学生），因此在我看来，这与找出
:fulltimers
属于
User
类型有关，即使我已经指定了
类名：“User”
中的
具有许多
条件

我做错了什么？
由于无法自动推断源关联，您需要使用
：source
选项指定它：

class Classroom < ActiveRecord::Base
  has_many(
    :fulltime_enrollments, 
    -> { where(duration: 'full-time') }, 
    class_name: "ClassroomEnrollments"
  )
  has_many :fulltimers, :through => :fulltime_enrollments, :source => :user

  has_many(
    :parttime_enrollments, 
    -> { where(duration: 'part-time') }, 
    class_name: "ClassroomEnrollments"
  )
  has_many :parttimers, :through => :parttime_enrollments, :source => :user
end

我在做类似的事情时偶然发现了这个。这将生成相同的sql，并且更易于查看

class Classroom < ActiveRecord::Base
  has_many :classroom_enrollments
  has_many :users, through: :classroom_enrollments

  def fulltimers
    users.merge(ClassroomEnrollment.full_time)
  end

  def parttimers
    users.merge(ClassroomEnrollment.part_time)
  end
end

class ClassroomEnrollment < ActiveRecord::Base
  belongs_to :user
  belongs_to :classroom

  scope :fulltime, ->{ where(duration: 'full-time') }
  scope :parttime, ->{ where(duration: 'part-time') }
end

class User < ActiveRecord::Base
  has_many :classroom_enrollments
  has_many :classrooms, :through => :classroom_enrollments
end

课堂{where（持续时间：'full-time'）}
作用域：兼职，->{where（持续时间：'part-time'）}
结束
类用户：教室注册
结束
这是否仍然提供类似于
我的教室。全日制
class Classroom < ActiveRecord::Base
  has_many :classroom_enrollments
  has_many :users, through: :classroom_enrollments

  def full_timers
    users_by_duration("full-time")
  end

  def part_timers
    users_by_duration("part-time")
  end

  private

  def users_by_duration(duration)
    users.where(classroom_enrollments: { duration: duration })
  end
end

my_classroom = Classroom.find(1)
my_classroom.full_timers

class Classroom < ActiveRecord::Base
  has_many :classroom_enrollments
  has_many :users, through: :classroom_enrollments

  def fulltimers
    users.merge(ClassroomEnrollment.full_time)
  end

  def parttimers
    users.merge(ClassroomEnrollment.part_time)
  end
end

class ClassroomEnrollment < ActiveRecord::Base
  belongs_to :user
  belongs_to :classroom

  scope :fulltime, ->{ where(duration: 'full-time') }
  scope :parttime, ->{ where(duration: 'part-time') }
end

class User < ActiveRecord::Base
  has_many :classroom_enrollments
  has_many :classrooms, :through => :classroom_enrollments
end