如何将两个has_many关联合并为一个？

This seems to be a fairly common problem over here, yet there is no definitive solution. To restate once again, say I have a model:

这似乎是一个相当普遍的问题，但没有确定的解决方案。再次重申，说我有一个模型：

def Model < ActiveRecord::Base
    has_many :somethings, ...
    has_many :otherthings, ...
end

The question is then how to add a third association :combined that combines the two? I know this can be done with :finder_sql and similar result can be achieved with a scope, but neither of these gives me an actual association. The whole point of this is to be able to use it for another association with :through and things like Model.first.combined.some_scope.count

问题是如何添加第三个关联：结合两者？我知道这可以用：finder_sql和类似的结果可以用范围实现，但这些都没有给我一个实际的关联。这一点的重点是能够将它用于另一个关联：通过和类似Model.first.combined.some_scope.count之类的东西

EDIT: the relevant portions of the actual code

编辑：实际代码的相关部分

class Donation < ActiveRecord::Base
    # either Project or Nonprofit       
    belongs_to :donatable, :polymorphic => true
    belongs_to :account
end

class Project < ActiveRecord::Base
    belongs_to :nonprofit
end

class Nonprofit < ActiveRecord::Base
    has_many :projects

    # donations can be either direct or through a project
    # the next two associations work fine on their own

    # has_many :donations, :as => :donatable, :through => :projects
    # has_many :donations, :as => :donatable

    has_many :donations, ....                       # how do I get both here,
    has_many :supporters, :through => :donations    # for this to work?
end

Thanks.

谢谢。

1 个解决方案

#1

If Something and Otherthing are sufficiently similar, use STI:

如果Something和Otherthing足够相似，请使用STI：

def Model < ActiveRecord::Base
  has_many :somethings
  has_many :otherthings
  has_many :genericthings
end

def Genericthing < Activerecord::Base
  # put a string column named "type" in the table
  belongs_to :model
end

def Something < Genericthing
end

def Otherthing < Genericthing
end