如何通过Ruby on Rails中的多对多关系获取Collection对象

Question

我关注的朋友

class Project < ActiveRecord::Base
  has_many :milestones_projects
  has_many :milestones, :through => :milestones_projects
  validates :projectname, :presence=>true, :length=> {:maximum=>250}, :uniqueness=>true
  validates :location,:presence=>true
end

class Milestone < ActiveRecord::Base
  has_many :milestones_projects
  has_many :projects, :through => :milestones_projects

  validates :name, :presence => true, :length => {:maximum => 250}
  validates :days, :presence => true, :length => {:maximum => 3}
  validates :stage, :presence => true
end


class MilestonesProjects < ActiveRecord::Base
  belongs_to :milestones,:foreign_key => 'milestone_id'
  belongs_to :projects,:foreign_key => 'project_id'
end

所以我在项目和里程碑之间有很多对很多的关系。

在irb中，我想获取集合对象，因此我正在使用以下方法

irb(main):001:0> me=Project.find(1)
=> #<Project id: 1, location_id: 1, projectname: "Sample 2", description: "Sample 2", i
spublished: true, created_at: "2011-09-02 08:26:41", updated_at: "2011-09-07 10:26:48">

这里的“我”是一个包含第一个项目详细信息的数组，现在我正在尝试获取与此项目相关的里程碑详细信息。为此，我尝试如下

irb(main):002:0> me.milestones

但这给了我错误

NameError：来自c：/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/activerecord-3.0.9/lib/ active_record / base.rb：1205：来自c的未初始化常量Project :: MilestonesProject compute_type' from c:/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/activerecord-3.0.9/lib/ active_record/reflection.rb:162:in从c：/RailsInstaller/Ruby1.8.7/lib/ruby/ gems / 1.8 / gems / activerecord-3.0.9 / lib / active_record / reflection.rb：162：in klass' from c:/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/activerecord-3.0.9/lib/ active_record/reflection.rb:346:in source_reflection'from c：/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/activerecord-3.0.9/lib/ active_record / reflection.rb：346：在collect' from c:/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/activerecord-3.0.9/lib/ active_record/reflection.rb:346:in '/ RailsInstaller / Ruby1.8.7 / lib / ruby​​ / gems / 1.8 / gems / activerecord-3.0.9 / lib / active_record / collect' from c:/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/activerecord-3.0.9/lib/ active_record/reflection.rb:346:in source_reflection中从c：/ RailsInstaller / Ruby1收集。 8.7 / lib / ruby​​ / gems / 1.8 / gems / activerecord-3.0.9 / lib / active_record / reflection.rb：377：in check_validity!' from c:/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/activerecord-3.0.9/lib/ active_record/associations/association_proxy.rb:61:in check_validity!' from c:/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/activerecord-3.0.9/lib/ active_record/associations/association_proxy.rb:61:in initialize'from c：/RailsInstaller/Ruby1.8.7 /lib/ruby/gems/1.8/gems/activerecord-3.0.9/lib/ active_record / associations / association_collection.rb：23：in initialize' from c:/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/activerecord-3.0.9/lib/ active_record/associations/has_many_association.rb:11:in initialize'from c：/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/activerecord-3.0.9/lib / active_record / associations.rb：1483：in new' from c:/RailsInstaller/Ruby1.8.7/lib/ruby/gems/1.8/gems/activerecord-3.0.9/lib/ active_record/associations.rb:1483:in里程碑中'from（irb）：2 from：0

朋友们请帮我

我需要执行一些命令，例如

milestone_count=project.milestones.size

Answer 1

谢谢你快速的回复！ 终于我找到了解决方案，这里发布的答案都是正确的。

我这样改变了我的模特

class Project < ActiveRecord::Base
  has_many :project_milestones
  has_many :milestones, :through => :project_milestones
end

class Milestone < ActiveRecord::Base  
  has_many :project_milestones
  has_many :projects, :through => :project_milestones
end

class ProjectMilestone < ActiveRecord::Base
  belongs_to :milestone,:foreign_key => 'milestone_id'
  belongs_to :project,:foreign_key => 'project_id'
end

Answer 2

我怀疑rails的命名约定就是问题所在。 Rails认为您的模型对象是单数，而数据库表是复数。 Rails可能会对名为MilestonesProjects的模型产生问题，应将其命名为MilestoneProject因为就是这样：一个Milestone与一个Project之间的关系。 看一下“ Active Record指南”第2.4节中的示例，其中使用单数和复数形式。

Answer 3

在您的MilestonesProjects模型中尝试此代码

class MilestonesProjects < ActiveRecord::Base
  belongs_to :milestone,:foreign_key => 'milestone_id'
  belongs_to :project,:foreign_key => 'project_id'
end