如何在 Rails 中的连接表中获取相关记录？

Question

在我的 Rails 应用程序中，people 可以有多个 projects，反之亦然：

# app/models/person.rb
class Person < ActiveRecord::Base
  has_many :people_projects
  has_many :projects, :through => :people_projects
end

# app/models/people_project.rb
class PeopleProject < ActiveRecord::Base 
  belongs_to :person
  belongs_to :project 
end

# app/models/project.rb
class Project < ActiveRecord::Base
  has_many :people_projects
  has_many :people, :through => :people_projects

  def self.search(person_id)
    if person_id
      where("person_id = ?", person_id) # not working because no person_id column in projects table
    else
      scoped
    end
  end
end

如何在我的ProjectsController 的index 视图中按person_id 过滤项目，例如通过使用这样的 URL：http://localhost:3000/projects?person_id=164

我无法理解这一点。请帮忙！谢谢...

Answer 1

Person 和 Project 模型的关联定义不完整。您还需要定义has_many :people_projects。

# app/models/person.rb
class Person < ActiveRecord::Base
  has_many :people_projects # <-- This line
  has_many :projects, :through => :people_projects
end

# app/models/project.rb
class Project < ActiveRecord::Base
  has_many :people_projects # <-- This line
  has_many :people, :through => :people_projects
end

# app/models/people_project.rb
# This is defined correctly
class PeopleProject < ActiveRecord::Base
  belongs_to :person
  belongs_to :project
end

详情请参考The has_many :through Association。

使用此定义，您将能够使用current_user.projects 获取当前用户的所有项目，就像您已经在ProjectsController#index 中所做的那样。

更新：

您可以在 search 方法中使用 joins 或 includes 并应用 where 条件。如下所示：

# app/models/project.rb
class Project < ActiveRecord::Base
  has_many :people_projects
  has_many :people, :through => :people_projects

  def self.search(person_id)
    if person_id
      includes([:people_projects, :people]).where("people.id = ?", person_id) 
    else
      scoped
    end
  end
end

Answer 2

projects 表中不会有 person_id，因为它是 has_manyhas_many 关系。

简单地@person.projects 将执行一个join btw person_projects & projects 表并返回适当的项目。

*我假设，current_user 返回一个 Person 对象。*

另外，完成您的模型定义。他们每个人都应该列出他们与 PeopleProjects 的关系

class Person < ActiveRecord::Base
  has_many :people_projects
  has_many :projects, :through => :people_projects
end

class Project < ActiveRecord::Base
  has_many :people_projects
  has_many :people, :through => :people_projects
end