为多对多关系编写范围

Question

我有一个包含 3 个模型的应用程序：Renters、Departments、Criteria。

# app/models/department.rb

class Department < ActiveRecord::Base
  attr_accessible :name, :abbr

  has_many :renter_departments
  has_many :renters, :through => :renter_departments
end

和

# app/models/criterium.rb

class Criterium < ActiveRecord::Base
  attr_accessible :name

  has_many :renter_criteria
  has_many :renters, :through => :renter_criteria
end

我正在尝试在 Renter 模型中创建两个范围，让我可以按部门和标准查找租户。

这是我的代码：

# app/models/renter.rb

class Renter < ActiveRecord::Base

  # Relationships
  has_many :renter_departments
  has_many :renter_criteria
  has_many :departments, :through => :renter_departments
  has_many :criteria, :through => :renter_criteria

  # Scopes
  scope :from_department, lambda { |abbr| joins(:departments).where("abbr = ?", abbr) }
  scope :has_criterium, lambda { |criterium| joins(:criteria).where("name = ?", criterium) }

end

使用

Renter.from_department("SCS")

或

Renter.has_criterium("Economic considerations")

独立工作。但是，当我尝试链接它们时，

Renter.from_department("SCS").has_criterium("Economic considerations")

我收到一条错误消息：

  Renter Load (0.3ms)  SELECT "renters".* FROM "renters" INNER JOIN "renter_departments" ON "renter_departments"."renter_id" = "renters"."id" INNER JOIN "departments" ON "departments"."id" = "renter_departments"."department_id" INNER JOIN "renter_criteria" ON "renter_criteria"."renter_id" = "renters"."id" INNER JOIN "criteria" ON "criteria"."id" = "renter_criteria"."criterium_id" WHERE (abbr = 'SCS') AND (name = 'Economic considerations')
SQLite3::SQLException: ambiguous column name: name: SELECT "renters".* FROM "renters" INNER JOIN "renter_departments" ON "renter_departments"."renter_id" = "renters"."id" INNER JOIN "departments" ON "departments"."id" = "renter_departments"."department_id" INNER JOIN "renter_criteria" ON "renter_criteria"."renter_id" = "renters"."id" INNER JOIN "criteria" ON "criteria"."id" = "renter_criteria"."criterium_id" WHERE (abbr = 'SCS') AND (name = 'Economic considerations')
ActiveRecord::StatementInvalid: SQLite3::SQLException: ambiguous column name: name: SELECT "renters".* FROM "renters" INNER JOIN "renter_departments" ON "renter_departments"."renter_id" = "renters"."id" INNER JOIN "departments" ON "departments"."id" = "renter_departments"."department_id" INNER JOIN "renter_criteria" ON "renter_criteria"."renter_id" = "renters"."id" INNER JOIN "criteria" ON "criteria"."id" = "renter_criteria"."criterium_id" WHERE (abbr = 'SCS') AND (name = 'Economic considerations')

另外，

>> Renter.from_department("SCS").class
=> ActiveRecord::Relation
>> Renter.has_criterium("Economic considerations").class
=> ActiveRecord::Relation

关于我做错了什么有什么想法吗？

Answer 1

您要加入的表中有多个 name 列。使WHERE 子句使用renters.name 或departments.name 或具有适当name 列的任何表。

Answer 2

您需要在您的范围内引用表名：

scope :from_department, lambda { |abbr| joins(:departments).where("departments.abbr = ?", abbr) }
scope :has_criterium, lambda { |criterium| joins(:criteria).where("criteria.name = ?", criterium) }