has_many：通过，自引用协会

Question

我有麻烦的自我引用协会、模型应该给妈一系列模式的left_chunks和right_chunks方法，但是每次我得到一个空阵列

源

class Chunk < ActiveRecord::Base
  has_many :left_bindings, :foreign_key => "left_chunk_id",
   :class_name => "ChunkChunk",
   :dependent => :destroy
  has_many :right_chunks, :through => :left_bindings
  has_many :right_bindings, :foreign_key => "right_chunk_id",
   :class_name => "ChunkChunk",
   :dependent => :destroy
  has_many :left_chunks, :through => :right_bindings
end

class ChunkChunk < ActiveRecord::Base
 belongs_to :left_chunk, :class_name => "Chunk", :foreign_key => "left_chunk_id"
 belongs_to :right_chunk, :class_name => "Chunk", :foreign_key => "right_chunk_id"
end

输出。/脚本/控制台

>> #first case
?> 
?> left = Chunk.new({:content => "chunk_one"}); left.save
=> true
>> right = Chunk.new({:content => "chunk_two"}); right.save
=> true
>> left.right_chunks << right
=> []
>> left.right_chunks
=> []
>> left.left_chunks
=> []
>> 
?> #second case
?> 
?> left = Chunk.new({:content => "chunk_three"}); left.save
=> true
>> right = Chunk.new({:content => "chunk_four"}); right.save
=> true
>> right.left_chunks << left
=> []
>> right.left_chunks
=> []
>> right.right_chunks
=> []

为什么大块不结在一起吗？

数据库之后，执行代码

mysql> select * from chunks;
+----+-------------+---------------------+---------------------+
| id | content     | created_at          | updated_at          |
+----+-------------+---------------------+---------------------+
|  1 | chunk_one   | 2010-02-14 12:11:22 | 2010-02-14 12:11:22 | 
|  2 | chunk_two   | 2010-02-14 12:11:22 | 2010-02-14 12:11:22 | 
|  3 | chunk_three | 2010-02-14 12:11:22 | 2010-02-14 12:11:22 | 
|  4 | chunk_four  | 2010-02-14 12:11:22 | 2010-02-14 12:11:22 | 
+----+-------------+---------------------+---------------------+

mysql> select * from chunk_chunks;
+----+---------------+----------------+---------------------+---------------------+
| id | left_chunk_id | right_chunk_id | created_at          | updated_at          |
+----+---------------+----------------+---------------------+---------------------+
|  1 |          NULL |              2 | 2010-02-14 12:11:22 | 2010-02-14 12:11:22 | 
|  2 |             3 |           NULL | 2010-02-14 12:11:22 | 2010-02-14 12:11:22 | 
+----+---------------+----------------+---------------------+---------------------+

任何想法？

Answer 1

你不说哪个版本的MySQL，红宝石或轨道。我只是想这有一个小测试的应用程序，它工作正常。我使用的PostgreSQL8.4.1在OS X10.6.我刚创建了一个空应用在轨道上2.3.5/红宝石1.8.7(2009-06-12补174)与"轨testapp"，然后增加了两个模型在块。rb：

class Chunk < ActiveRecord::Base
  has_many :left_bindings,  :foreign_key => "left_chunk_id",
                            :class_name => "ChunkChunk",
                            :dependent => :destroy
  has_many :right_chunks,   :through => :left_bindings
  has_many :right_bindings, :foreign_key => "right_chunk_id",
                            :class_name => "ChunkChunk",
                            :dependent => :destroy
  has_many :left_chunks,    :through => :right_bindings
end

...和chunk_chunks.rb：

class ChunkChunk < ActiveRecord::Base
 belongs_to :left_chunk,  :class_name => "Chunk", :foreign_key => "left_chunk_id"
 belongs_to :right_chunk, :class_name => "Chunk", :foreign_key => "right_chunk_id"
end

...加上两个迁移到加的表格，而没有时间戳，为了简洁起见:

class AddChunks < ActiveRecord::Migration
  def self.up
    create_table 'chunks' do | t |
      t.string :content
    end
  end

  def self.down
    drop_table 'chunk'
  end
end

...并且：

class AddChunkChunks < ActiveRecord::Migration
  def self.up
    create_table 'chunk_chunks' do | t |
      t.belongs_to :left_chunk
      t.belongs_to :right_chunk
    end
  end

  def self.down
  end
end

然后我跑"耙db：创建"、"瑞克db:迁移"和你的控制台的命令为我工作如下：

PondPro:testapp adh1003$ script/console
Loading development environment (Rails 2.3.5)
>> left = Chunk.new({:content => "chunk_one"}); left.save
=> true
>> right = Chunk.new({:content => "chunk_two"}); right.save
=> true
>> left.right_chunks << right
=> [#<Chunk id: 2, content: "chunk_two">]
>> left.right_chunks
=> [#<Chunk id: 2, content: "chunk_two">]
>> left.left_chunks
=> []
>> left = Chunk.new({:content => "chunk_three"}); left.save
=> true
>> right = Chunk.new({:content => "chunk_four"}); right.save
=> true
>> right.left_chunks << left
=> [#<Chunk id: 3, content: "chunk_three">]
>> right.left_chunks
=> [#<Chunk id: 3, content: "chunk_three">]
>> right.right_chunks
=> []

数据库内容之后，上述：

chunk-devel=# SELECT * FROM chunks;
 id |   content   
----+-------------
  1 | chunk_one
  2 | chunk_two
  3 | chunk_three
  4 | chunk_four
(4 rows)

chunk-devel=# SELECT * FROM chunk_chunks;
 id | left_chunk_id | right_chunk_id 
----+---------------+----------------
  1 |             1 |              2
  2 |             3 |              4
(2 rows)

鉴于这样的：

• http://blog.hasmanythrough.com/2006/4/21/self-referential-through

...和这样的：

• http://blog.hasmanythrough.com/2007/10/30/self-referential-has-many-through

...我什么都看不到真的错了你的原始代码。也许迁移不是你所期望的，也许还有其它的部份你代码你还没有公布这是干扰(例如过滤器，其他宝石)，或者也许Email数据库的适配器MySQL不是在做正确的事情，在这种情况下和/或MySQL不执行不适当的。这是一个有点啰嗦安装PostgreSQL和使用，而不是MySQL为进一步的试验，但我认为这将是值得的。

只要的情况下，它被证明在所有有用的我已经上传测试的应用程序的数据：

• http://pond.org.uk/misc/for_messages/chunks_testapp.tar.gz

如果你找到了什么差错和管理，以纠正，请后续在这里。这将是有用的，如果任何人遭遇的类似麻烦，在未来和读取这一线的同时，寻找一个解决方案。

Answer 2

这是一个.reload问题？当您在控制台中做到这一点：

right.left_chunks << left

DO

right.reload

然后尝试

right.left_chunks。