PROSAGA码农传奇-关联管理-在Rails 3中构建与新

您稍微误读了文档。some_firm.client.new正在Client从客户集合中创建一个新对象，因此它可以自动将设置firm_id为some_firm.id，而文档正在调用Client.new而根本不知道任何公司的ID，因此需要将其firm_id传递给它。

some_firm.clients.new和之间的唯一区别some_firm.clients.build似乎是，它build还将新创建的客户端添加到clients集合中：

```
henrym:~/testapp$ rails c
Loading development environment (Rails 3.0.4)
r:001 > (some_firm = Firm.new).save # Create and save a new Firm
#=> true 
r:002 > some_firm.clients           # No clients yet
#=> [] 
r:003 > some_firm.clients.new       # Create a new client
#=> #<Client id: nil, firm_id: 1, created_at: nil, updated_at: nil> 
r:004 > some_firm.clients           # Still no clients
#=> [] 
r:005 > some_firm.clients.build     # Create a new client with build
#=> #<Client id: nil, firm_id: 1, created_at: nil, updated_at: nil> 
r:006 > some_firm.clients           # New client is added to clients 
#=> [#<Client id: nil, firm_id: 1, created_at: nil, updated_at: nil>] 
r:007 > some_firm.save
#=> true 
r:008 > some_firm.clients           # Saving firm also saves the attached client
#=> [#<Client id: 1, firm_id: 1, created_at: "2011-02-11 00:18:47",
updated_at: "2011-02-11 00:18:47">] 
```
如果要通过关联创建对象，build则应优先考虑new构建，因为some_firm即使在将任何对象保存到数据库之前，构建仍将内存中的对象（在这种情况下）保持一致的状态。