Ruby on rails 在属于ActiveRecord关联的文件上使用through选项

有没有办法在归属关系中通过使用

选项？没有提到通过

作为选项，为什么不呢？我想做如下事情：

class Lesson < ActiveRecord::Base
  attr_accessible :name, :lesson_group_id
  belongs_to :lesson_group
  belongs_to :level, through: :lesson_group
end

class LessonGroup < ActiveRecord::Base
  attr_accessible :name, :level_id
  belongs_to :level
  has_many :lessons
end

class Level < ActiveRecord::Base
  attr_accessible :number
  has_many :lesson_groups
end

class Lesson < ActiveRecord::Base
  attr_accessible :name, :lesson_group_id
  belongs_to :lesson_group
  has_one :level, through: :lesson_group
end

class LessonGroup < ActiveRecord::Base
  attr_accessible :name, :level_id
  belongs_to :level
  has_many :lessons
end

class Level < ActiveRecord::Base
  attr_accessible :number
  has_many :lesson_groups
end

课程

然后我可以做一些类似于

Lesson.first.level

的事情。使用最新的稳定轨道（目前为3.2.9）。

中给出了：

指定与另一个类的一对一关联。仅当此类包含外键时才应使用此方法

我认为您应该使用

has\u one:level，through:：lesson\u group

，如下所示：

class Lesson < ActiveRecord::Base
  attr_accessible :name, :lesson_group_id
  belongs_to :lesson_group
  belongs_to :level, through: :lesson_group
end

class LessonGroup < ActiveRecord::Base
  attr_accessible :name, :level_id
  belongs_to :level
  has_many :lessons
end

class Level < ActiveRecord::Base
  attr_accessible :number
  has_many :lesson_groups
end

class Lesson < ActiveRecord::Base
  attr_accessible :name, :lesson_group_id
  belongs_to :lesson_group
  has_one :level, through: :lesson_group
end

class LessonGroup < ActiveRecord::Base
  attr_accessible :name, :level_id
  belongs_to :level
  has_many :lessons
end

class Level < ActiveRecord::Base
  attr_accessible :number
  has_many :lesson_groups
end

课程

有关

选项的文档中有一部分包含以下内容：

：通过

指定要通过其执行查询的联接模型。选项为：类名称、：主键和：外键
忽略，因为关联使用源反射。你只能
使用：通过在上具有关联或属于关联的
连接模型

他们在这里谈到了这一点：
在
Rails 6
，
Ruby 2.6
中，我遇到了一个类似的问题，我有一个
用户
，可能属于许多
组织
，但总是有一个
主要组织
，这是他们被分配到的第一个
组织
。最初，我使用以下方法设置此选项：

def primary_organization
  organizations.first
end

然而，这最终打破了我的范围链。上述
primary\u-organization
方法可以重构为可链接的条件，而无需更改
用户。primary\u-organization
语法：

user.rb

# has_many: OrganizationUsers > Organizations
# ==================================================================================
has_many    :organization_users,
              class_name:     'OrganizationUser',
              inverse_of:     :user,
              dependent:      :destroy,
              autosave:       true,

has_many    :organizations,
              class_name:     'Organization',
              through:        :organization_users,
              inverse_of:     :organization_users,
              source:         :organization

# *** ADDED IN REFACTOR ***
# has_one: Organization
# shortcut for:
#   • `user.organization_users.first.organization`
#   • `user.organizations.first`
# ==================================================================================
has_one     :primary_organization_user,
              -> {
                order(
                  created_at: :desc
                ).limit(1)
              },
              class_name:     'OrganizationUser',
              inverse_of:     :user

has_one     :primary_organization,
              class_name:     'Organization',
              through:        :primary_organization_user,
              inverse_of:     :organization_users,
              source:         :organization

# belongs_to: Organization
# ==================================================================================
belongs_to  :organization,
              class_name:     'Organization',
              inverse_of:     :organization_users

# belongs_to: User
# ==================================================================================
belongs_to  :user,
              class_name:     'User',
              inverse_of:     :organization_users

# has_many: OrganizationUsers > Users
# ==================================================================================
has_many    :organization_users,
              class_name:     'OrganizationUser',
              inverse_of:     :organization,
              autosave:       true,
              dependent:      :destroy

has_many    :users,
              class_name:     'User',
              through:        :organization_users,
              inverse_of:     :organization_users,
              autosave:       true

组织机构\u用户.rb

# has_many: OrganizationUsers > Organizations
# ==================================================================================
has_many    :organization_users,
              class_name:     'OrganizationUser',
              inverse_of:     :user,
              dependent:      :destroy,
              autosave:       true,

has_many    :organizations,
              class_name:     'Organization',
              through:        :organization_users,
              inverse_of:     :organization_users,
              source:         :organization

# *** ADDED IN REFACTOR ***
# has_one: Organization
# shortcut for:
#   • `user.organization_users.first.organization`
#   • `user.organizations.first`
# ==================================================================================
has_one     :primary_organization_user,
              -> {
                order(
                  created_at: :desc
                ).limit(1)
              },
              class_name:     'OrganizationUser',
              inverse_of:     :user

has_one     :primary_organization,
              class_name:     'Organization',
              through:        :primary_organization_user,
              inverse_of:     :organization_users,
              source:         :organization

# belongs_to: Organization
# ==================================================================================
belongs_to  :organization,
              class_name:     'Organization',
              inverse_of:     :organization_users

# belongs_to: User
# ==================================================================================
belongs_to  :user,
              class_name:     'User',
              inverse_of:     :organization_users

# has_many: OrganizationUsers > Users
# ==================================================================================
has_many    :organization_users,
              class_name:     'OrganizationUser',
              inverse_of:     :organization,
              autosave:       true,
              dependent:      :destroy

has_many    :users,
              class_name:     'User',
              through:        :organization_users,
              inverse_of:     :organization_users,
              autosave:       true

organization.rb

# has_many: OrganizationUsers > Organizations
# ==================================================================================
has_many    :organization_users,
              class_name:     'OrganizationUser',
              inverse_of:     :user,
              dependent:      :destroy,
              autosave:       true,

has_many    :organizations,
              class_name:     'Organization',
              through:        :organization_users,
              inverse_of:     :organization_users,
              source:         :organization

# *** ADDED IN REFACTOR ***
# has_one: Organization
# shortcut for:
#   • `user.organization_users.first.organization`
#   • `user.organizations.first`
# ==================================================================================
has_one     :primary_organization_user,
              -> {
                order(
                  created_at: :desc
                ).limit(1)
              },
              class_name:     'OrganizationUser',
              inverse_of:     :user

has_one     :primary_organization,
              class_name:     'Organization',
              through:        :primary_organization_user,
              inverse_of:     :organization_users,
              source:         :organization

# belongs_to: Organization
# ==================================================================================
belongs_to  :organization,
              class_name:     'Organization',
              inverse_of:     :organization_users

# belongs_to: User
# ==================================================================================
belongs_to  :user,
              class_name:     'User',
              inverse_of:     :organization_users

# has_many: OrganizationUsers > Users
# ==================================================================================
has_many    :organization_users,
              class_name:     'OrganizationUser',
              inverse_of:     :organization,
              autosave:       true,
              dependent:      :destroy

has_many    :users,
              class_name:     'User',
              through:        :organization_users,
              inverse_of:     :organization_users,
              autosave:       true

@MrYoshiji-在
has_one
下，Rails文档说，“只有当其他类包含外键时才应使用此方法。如果当前类包含外键，则应使用belish to.。”
的文档中也有“Options:[…]-：through指定要通过其执行查询的联接模型。由于关联使用源反射，将忽略：class_name、：primary_key和：foreign_key的选项。您只能通过联接模型上的has_one或归属于关联使用：through查询。“这似乎没有意义。”<代码>课程
的
属于：课程组
存在，因为它没有外键。类似地，
LessonGroup
的
属于：level
存在，因为它有外键。我会尝试这种方法，但不愿意依赖这种机制，即使它可以工作，因为文档中根本没有明确说明在这种情况下使用
has_one
。我同意，这种情况不清楚。这可能会让您有点感兴趣：
所属\u to:to C
不存在，因为当前表不包含指向
C
的外键。