ActiveRecord 中与多个自联接的多对多关联

Question

我正在尝试通过自连接实现同一模型的记录之间的多种关系（基于 @Shtééf 的回答）。我有以下模型

create_table :relations, force: true do |t|
  t.references :employee_a
  t.string     :rel_type
  t.references :employee_b
end

class Relation < ActiveRecord::Base
  belongs_to :employee_a, :class_name => 'Employee'
  belongs_to :employee_b, :class_name => 'Employee'
end

class Employee < ActiveRecord::Base
  has_many :relations, foreign_key: 'employee_a_id'
  has_many :reverse_relations, class_name: 'Relation', foreign_key: 'employee_b_id'

  has_many :subordinates, through: :relations, source: 'employee_b', conditions: {'relations.rel_type' => 'manager of'}
  has_many :managers, through: :reverse_relations, source: 'employee_a', conditions: {'relations.rel_type' => 'manager of'}
end

通过此设置，我可以成功访问每条记录的下属和经理列表。但是，我很难通过以下方式创建关系。

e = Employee.create
e.subordinates.create
e.subordinates #=> []
e.managers.create
e.managers #=> []

问题是它没有设置关系类型，所以我必须写

e = Employee.create
s = Employee.create
e.relations.create employee_b: s, rel_type: 'manager of'
e.subordinates #=> [#<Employee id:...>]

我做错了什么吗？

Answer 1

您可以在 has_many 关联上使用 before_add 和 before_remove 回调：

class Employee < ActiveRecord::Base
  has_many :relations, foreign_key: 'employee_a_id'
  has_many :reverse_relations, class_name: 'Relation', foreign_key: 'employee_b_id'

  has_many :subordinates, 
           through: :relations, 
           source: 'employee_b', 
           conditions: {'relations.rel_type' => 'manager of'}
           :before_add => Proc.new { |employe,subordinate| employe.relations.create(employe_b: subordinate, rel_type: 'manager of') },
           :before_remove => Proc.new { |employe,subordinate| employe.relations.where(employe_b: subordinate, rel_type: 'manager of').first.destroy }

  has_many :managers,  
           through: :reverse_relations, 
           source: 'employee_a', 
           conditions: {'relations.rel_type' => 'manager of'}
           :before_add => Proc.new { |employe,manager| employe.reverse_relations.create(employe_a: manager, rel_type: 'manager of') },
           :before_remove => Proc.new { |employe,manager| employe.reverse_relations.where(employe_b: subordinate, rel_type: 'manager of').first.destroy }

这应该有效，并使您能够使用 employe.managers.create
您可能希望在回调中使用 build 而不是 create
您还可以阅读有关此解决方案的此问题

Answer 2

为了创建多个多对多自联接关联，我建议使用多个表来管理连接可能更有意义。这样，从数据的角度来看，到底发生了什么就非常清楚，从逻辑的角度来看也很清楚。因此，沿着这些思路：

create_table :manage_relation do |t|
  t.references :employee_id
  t.references :manager_id
end
create_table :subordinate_relation do |t|
  t.references :employee_id
  t.references :subordinate_id
end

class Employee < ActiveRecord::Base

  has_many :subordinates, 
           :through => :subordinate_relation, 
           :class_name => "Employee", 
           :foreign_key => "subordinate_id"
  has_many :managers, 
           :through => :manage_relation, 
           :class_name => "Employee", 
           :foreign_key => "manager_id"

  belongs_to :employee, 
             :class_name => "Employee"
end

这样，从编码的角度来看，它不会变得比必要的更加复杂，并且您可以使用标准集合访问它，并且它将适当地为您设置连接，而无需您管理它们。因此，这两个集合都应该有效。

employee.managers
employee.subordinates

并且您不必管理任何其他变量。有道理吗？它添加了一个表格，但提高了清晰度。

Answer 3

我将按如下方式重做您的模型：

class ManagerRelation < ActiveRecord::Base
  belongs_to :manager, :class_name => 'Employee'
  belongs_to :subordinate, :class_name => 'Employee'
end

class Employee < ActiveRecord::Base
  has_many :manager_relations,     :class_name => "ManagerRelation",
               :foreign_key => :subordinate_id
  has_many :subordinate_relations, :class_name => "ManagerRelation", 
               :foreign_key => :manager_id

  has_many :managers,     :source => :manager,     
               :through => :manager_relations

  has_many :subordinates, :source => :subordinate, 
               :through => :subordinate_relations
end

现在您可以执行以下操作：

employee.managers
employee.subordinates    
employee.managers << employee2    
employee.subordinates << employee3

注意：当一个人被迫向两位经理汇报时，这通常是一个人离开公司的标志:-)

Answer 4

鉴于所提出的关系，

create_table :relations, force: true do |t|
  t.references :employee_a
  t.string     :rel_type
  t.references :employee_b
end


class Employee < ActiveRecord::Base

  has_many :subordinate_relations, :class_name => "Relation", :conditions => {:rel_type => 'manager of'}, :foreign_key => :employee_a
  has_many :subordinates, :through => :subordinate_relations, :source => :subordinate, :foreign_key => :employee_b

  has_many :manager_relations, :class_name => "Relation", :conditions => {:rel_type => 'manager of'}, :foreign_key => :employee_b
  has_many :managers, :through => :manager_relations, :source => :manager, :foreign_key => :employee_a

end


class Relation < ActiveRecord::Base

  belongs_to :manager, :class_name => "Employee", :foreign_key => :employee_a
  belongs_to :subordinate, :class_name => "Employee", :foreign_key => :employee_b

end


e = Employee.create
e.subordinates.create #Employee ...
e.subordinates #[<Employee ...]

e2 = Employee.create
e2.managers.create #Employee
e2.managers #[<Employee ...]

尽管解决方案有效 - 我对将关联与“rel_type”联系起来感到有点困惑。在这种情况下 - 我想说 rel_type 是多余的，关系应该映射如下：

create_table :relations do |t|
    t.reference :manager
    t.reference :subordinate
end

在这种情况下，关联映射应该更简单一些。