ruby-on-rails – 渴望加载“有很多通过” – 我需要Arel吗？

我有三个表：用户,成员,项目.中间是一个连接表,表示其他两个表之间的has-many-through;它有一些感兴趣的属性,包括join_code和激活.

更广泛地：

class User < ActiveRecord::Base
  has_many :members
  has_many :projects,:through => :members
end

class Member < ActiveRecord::Base
  belongs_to :user
  belongs_to :project
  # has a column called join_code
  # has a column called activated
  # Note that this class can be thought of as "membership"
end

class Project < ActiveRecord::Base
  has_many :members
  has_many :users,:through => :members
end

目标：给定一个特定的用户,我想要一个能够获得所有项目的查询,并且只需要加载将这些项目链接到用户的成员记录.

到目前为止,我在user.rb中有这个方法来执行查询：

def live_projects
  self.projects.order("projects.name").includes(:members).where(:members => {:join_code => nil,:activated => true})
end

但这还不够.我希望能够在视图代码中执行此操作：

<% current_user.live_projects.each do |project| %>
  <li project_id="<%= project.id %>">
    <% member = project.member %>
      (Do something with that member record here)
      <%= project.name %>
    <% end %>
  </li>
<% end %>

在这里,通常,我有project.members,但在我的上下文中,我只对那个链接回用户的成员记录感兴趣.

这就是我认为原始sql应该是什么样子

select projects.*,members.* 
from projects inner join members on projects.id = members.project_id
where members.user_id = X and members.join_code is null and members.activated = 't';

如何在Arel(或ActiveRecord)中执行此操作？

解决方法

我可能在这里有一些答案,即我写的ActiveRecord代码似乎很合理.再次,这是查询：

def live_projects
  self.projects.order("projects.name").includes(:members).where(:members => {:join_code => nil,:activated => true})
end

在使用示例数据运行UI时,它会从Rails服务器生成此输出：

Project Load (0.6ms)  SELECT "projects".* FROM "projects" INNER JOIN "members" ON "projects".id = "members".project_id WHERE "members"."join_code" IS NULL AND "members"."activated" = 't' AND (("members".user_id = 3)) ORDER BY projects.name
Member Load (2.0ms)  SELECT "members".* FROM "members" WHERE ("members".project_id IN (50,3,6,37,5,1))

然后在视图代码中我可以这样做：

<% current_user.live_projects.each do |project| %>
  <li project_id="<%= project.id %>" class="<%= 'active' if project == @project %>">
    <% member = project.members.detect { |member| member.user_id == current_user.id } %>
    (Do something with that member record here)
  </li>
<% end %>

获取成员记录的表达式在视图中非常难看,但select是一个Array方法,而不是查询,除了上面显示的两个以外,没有额外的DB命中出现在Rails服务器的输出中.因此,我想我的n 1问题已经解决了.