自指has_many故障

Question

我在一个自我引用的桌子上遇到麻烦。

我有一个能容纳行星、恒星和卫星的球体模型。我想告诉你一件“轨道”另一件事

我看了导轨，但我不能让它工作。

我的模特：

class Orb < ActiveRecord::Base
  belongs_to :orb_type
  has_and_belongs_to_many :books

  belongs_to :orbit, :class_name => "Orb"
  has_many :orbs, :class_name => "Orb", :foreign_key => "orb_id"

  attr_accessible :descr, :nome, :orb_type_id, :book_ids, :orb_id

  validates :nome, uniqueness: true, presence: true
end

我想我用的是关系不好的名字(可能是错误的)。

1.9.3-p448 :002 > earth = Orb.find(1)
  Orb Load (0.2ms)  SELECT "orbs".* FROM "orbs" WHERE "orbs"."id" = ? LIMIT 1  [["id", 1]]
 => #<Orb id: 1, nome: "Terra", descr: "123123", orb_type_id: 1, created_at: "2013-09-25 14:53:35", updated_at: "2013-09-25 14:57:40", orb_id: nil> 
1.9.3-p448 :003 > moon = Orb.find(2)
  Orb Load (0.2ms)  SELECT "orbs".* FROM "orbs" WHERE "orbs"."id" = ? LIMIT 1  [["id", 2]]
 => #<Orb id: 2, nome: "Lua", descr: "asd", orb_type_id: 2, created_at: "2013-09-25 14:53:46", updated_at: "2013-09-25 14:55:31", orb_id: nil> 
1.9.3-p448 :004 > sun = Orb.find(3)
  Orb Load (0.2ms)  SELECT "orbs".* FROM "orbs" WHERE "orbs"."id" = ? LIMIT 1  [["id", 3]]
 => #<Orb id: 3, nome: "Sol", descr: "asd", orb_type_id: 3, created_at: "2013-09-25 14:53:55", updated_at: "2013-09-25 14:53:55", orb_id: nil> 
1.9.3-p448 :006 > moon.orbit=earth
 => #<Orb id: 1, nome: "Terra", descr: "123123", orb_type_id: 1, created_at: "2013-09-25 14:53:35", updated_at: "2013-09-25 14:57:40", orb_id: nil> 
1.9.3-p448 :007 > earth.orbit=sun
 => #<Orb id: 3, nome: "Sol", descr: "asd", orb_type_id: 3, created_at: "2013-09-25 14:53:55", updated_at: "2013-09-25 14:53:55", orb_id: nil> 
1.9.3-p448 :008 > earth
 => #<Orb id: 1, nome: "Terra", descr: "123123", orb_type_id: 1, created_at: "2013-09-25 14:53:35", updated_at: "2013-09-25 14:57:40", orb_id: nil> 
1.9.3-p448 :009 > sun
 => #<Orb id: 3, nome: "Sol", descr: "asd", orb_type_id: 3, created_at: "2013-09-25 14:53:55", updated_at: "2013-09-25 14:53:55", orb_id: nil> 
1.9.3-p448 :010 > moon
 => #<Orb id: 2, nome: "Lua", descr: "asd", orb_type_id: 2, created_at: "2013-09-25 14:53:46", updated_at: "2013-09-25 14:55:31", orb_id: nil> 

最终什么都没有联系到，FK仍然没有联系。

在模型中加入了orb_id。我设置了一个迁移并将其添加到模型中。我不认为这和我的问题有关.

编辑：

现在每件事都很奇怪。我把我的模型改为：

class Orb < ActiveRecord::Base
  belongs_to :orb_type
  has_and_belongs_to_many :books

  belongs_to :orbit, :class_name => "Orb"
  has_many :orbits, :class_name => "Orb", :foreign_key => "orb_id"

  attr_accessible :descr, :nome, :orb_type_id, :book_ids, :orb_id

  validates :nome, uniqueness: true, presence: true
end

在rails控制台(rails c)中，我尝试：

1.9.3-p448 :008 > earth = Orb.find(1)
  Orb Load (0.2ms)  SELECT "orbs".* FROM "orbs" WHERE "orbs"."id" = ? LIMIT 1  [["id", 1]]
 => #<Orb id: 1, nome: "Terra", descr: "", orb_type_id: 1, created_at: "2013-09-25 17:51:26", updated_at: "2013-09-25 18:16:58", orb_id: 3> 
1.9.3-p448 :009 > earth.orbit
 => nil 
1.9.3-p448 :010 > earth.orbits
  Orb Load (0.3ms)  SELECT "orbs".* FROM "orbs" WHERE "orbs"."orb_id" = 1
 => [#<Orb id: 2, nome: "Lua", descr: "", orb_type_id: 2, created_at: "2013-09-25 17:51:40", updated_at: "2013-09-25 18:17:31", orb_id: 1>] 
1.9.3-p448 :011 > 

什么鬼东西？轨道可以返回我想要的东西，但我试着用它：

1.9.3-p448 :004 > earth.orbits.nome
NoMethodError:   Orb Load (0.4ms)  SELECT "orbs".* FROM "orbs" WHERE "orbs"."orb_id" = 1
undefined method `nome' for #<ActiveRecord::Relation:0x00000003d593c0>
        from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/activerecord-3.2.12/lib/active_record/relation/delegation.rb:45:in `method_missing'
        from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/activerecord-3.2.12/lib/active_record/associations/collection_proxy.rb:100:in `method_missing'
        from (irb):4
        from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/railties-3.2.12/lib/rails/commands/console.rb:47:in `start'
        from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/railties-3.2.12/lib/rails/commands/console.rb:8:in `start'
        from /usr/local/rvm/gems/ruby-1.9.3-p448/gems/railties-3.2.12/lib/rails/commands.rb:41:in `<top (required)>'
        from script/rails:6:in `require'
        from script/rails:6:in `<main>'

Answer 1

我想明白了。我应该使表中的rom使用关系名称(orbit_id)，而不是表名(orb_id)。

)修复一切开始很好地工作:)

has_many :orbters, class_name: "Orb", foreign_key: "orbit_id"
belongs_to :orbit, class_name: "Orb"

Answer 2

从技术上讲，行星、恒星和卫星都在同一个模型中，这并不好。他们的行为都不一样，每个人都应该有自己的模式。例如，一颗恒星永远不会绕着一颗行星转，而一颗行星也永远不会绕着月亮转(根据定义)。通过以现有的方式构造数据库，您正在为损坏的数据设置自己，如果允许的话，这种情况将始终发生。

如果您必须将它们全部包含在Orb模型中，我将推荐两种模型:一种用于Orbs (恒星、行星、卫星)，一种用于Orbits。Orbit类本质上是一个如下所示的表：

Orbit model:

| id | orbited_id | orbiter_id |
--------------------------------
|  0 | planet_id  | moon_id    |
|  1 | star_id    | planet_id  |
|  2 | planet_id  | moon_id    |
| ...| etc        | etc        |

然后可以在orb.rb中设置关联：

has_and_belongs_to_many :orbits,
                        class_name: 'Orb',
                        join_table: :orbits,
                        foreign_key: :orbited_id,
                        association_foreign_key: :orbiter_id,
                        uniq: true

这样你就可以做这样的事情

>> sun = Orb.find(1)
>> sun.orbits
=> [ <Orb mercury>, <Orb venus>, ..., <Orb pluto> ]