Question

我现在宣读:。

我发现,根据你如何安排协会,你选择自己或归属。

但是,如果在以下几个方面存在差异,我并不完全清楚。

Declare X has_one Y or Y belong_to X
Declare X has_one Y AND Y belong_to X

So is there any case where you have to explicitly say X has_one Y and Y belong_to X ? Or is it always sufficient to say either X has_one Y or Y belong_to X.

Answer 1

具有: 添加相关物体检索和收集方法。

属于: 添加该物体所持有的单一相关物体的检索和查询方法

so, if you dont require to use methods on both the associated objects you may choose not the set the association accordingly.But its mandatory to put the foreign key in the model where the one instance is associated to one and only one instance of the other object that is: belongs_to model.

解释:

让我们考虑像样:

create_table "cars", :force => true do |t|
t.integer  "user_id"
t.datetime "created_at"
t.datetime "updated_at"
end

create_table "users", :force => true do |t|
t.datetime "created_at"
t.datetime "updated_at"
end

模式如下:

class User < ActiveRecord::Base
end

class Car < ActiveRecord::Base
belongs_to :user
end

结果是:

D:	emp>rails c
Loading development environment (Rails 3.0.10)
irb(main):001:0> U = User.first
=> #<User id: 1, created_at: "2011-11-22 06:43:04", updated_at: "2011-11-22 06:43:04">

irb(main):002:0> C = Car.first
=> #<Car id: 1, user_id: 1, created_at: "2011-11-22 06:43:34", updated_at: "2011-11-22 06:43:34">
irb(main):003:0> C.user
=> #<User id: 1, created_at: "2011-11-22 06:43:04", updated_at: "2011-11-22 06:43:04">
irb(main):004:0> U.cars
NoMethodError: undefined method `cars  for #<User:0x3d19970>
from C:/Ruby/lib/ruby/gems/1.9.1/gems/activemodel-3.0.10/lib/active_model/attribute_methods.rb:392:in `method_missing 
    from C:/Ruby/lib/ruby/gems/1.9.1/gems/activerecord-3.0.10/lib/active_record/attribute_methods.rb:46:in `method_missing 
    from (irb):4
    from C:/Ruby/lib/ruby/gems/1.9.1/gems/railties-3.0.10/lib/rails/commands/console.rb:44:in `start 
    from C:/Ruby/lib/ruby/gems/1.9.1/gems/railties-3.0.10/lib/rails/commands/console.rb:8:in `start 
    from C:/Ruby/lib/ruby/gems/1.9.1/gems/railties-3.0.10/lib/rails/commands.rb:23:in `<top (required)> 
    from script/rails:6:in `require 
    from script/rails:6:in `<main> 
irb(main):005:0> exit

如果模式如下:

模式如下:

class User < ActiveRecord::Base
has_many :cars
end

class Car < ActiveRecord::Base
end

结果:

D:	emp>rails c
Loading development environment (Rails 3.0.10)
irb(main):001:0> U = User.first
=> #<User id: 1, created_at: "2011-11-22 06:43:04", updated_at: "2011-11-22 06:43:04">
irb(main):002:0> C = Car.first
=> #<Car id: 1, user_id: 1, created_at: "2011-11-22 06:43:34", updated_at: "2011-11-22 06:43:34">
irb(main):003:0> U.cars
=> [#<Car id: 1, user_id: 1, created_at: "2011-11-22 06:43:34", updated_at: "2011-11-22 06:43:34">]
irb(main):004:0> C.user
NoMethodError: undefined method `user  for #<Car:0x41524c8>
    from C:/Ruby/lib/ruby/gems/1.9.1/gems/activemodel-3.0.10/lib/active_model/attribute_methods.rb:392:in `method_missing 
    from C:/Ruby/lib/ruby/gems/1.9.1/gems/activerecord-3.0.10/lib/active_record/attribute_methods.rb:46:in `method_missing 
    from (irb):4
    from C:/Ruby/lib/ruby/gems/1.9.1/gems/railties-3.0.10/lib/rails/commands/console.rb:44:in `start 
    from C:/Ruby/lib/ruby/gems/1.9.1/gems/railties-3.0.10/lib/rails/commands/console.rb:8:in `start 
    from C:/Ruby/lib/ruby/gems/1.9.1/gems/railties-3.0.10/lib/rails/commands.rb:23:in `<top (required)> 
    from script/rails:6:in `require 
    from script/rails:6:in `<main> 
irb(main):005:0>

Answer 2

你们不要再说什么?

所有方法都是在它们重新使用的类别中增加额外的方法/元数据:如果你不想要/利用这些方法,就不需要添加这些方法。

添加的方法见:http://guides.rubyonrails.org/association_basics.html#detailed-association-vis”rel=“nofollow” 。

友情链接