Ruby-on-rails 可以在 Rails 中给关联关联别名吗？

Possible to alias a belongs_to association in Rails?

提问by at.

I have a model with a belongs_toassociation:

我有一个带有belongs_to关联的模型：

class Car < ActiveRecord::Base
  belongs_to :vendor
end

So I can call car.vendor. But I also want to call car.company! So, I have the following:

所以我可以打电话car.vendor。但我也想打电话car.company！所以，我有以下几点：

class Car < ActiveRecord::Base
  belongs_to :vendor
  def company
    vendor
  end
end

but that doesn't solve the assignment situation car.company = 'ford', so I need to create another method for that. Is there a simple aliasmechanism I can use for associations? Can I just use alias_method :company, :vendorand alias_method :company=, :vendor=?

但这并不能解决分配情况car.company = 'ford'，所以我需要为此创建另一种方法。是否有一种简单的alias机制可以用于关联？我可以只使用alias_method :company, :vendorandalias_method :company=, :vendor=吗？

回答by pramod

No it doesn't look for company_id for instance change your code as follows

不，它不会查找 company_id 例如更改您的代码如下

In Rails3

在 Rails3 中

class Car < ActiveRecord::Base
   belongs_to :vendor
   belongs_to :company, :class_name => :Vendor,:foreign_key => "vendor_id"
end

In Rails4

在 Rails4 中

We can use alias attribute.

我们可以使用别名属性。

alias_attribute :company, :vendor

回答by Fran Worley

In Rails 4, you should simply be able to add alias_attribute :company, :vendorto your model.

在 Rails 4 中，您应该能够简单地添加alias_attribute :company, :vendor到您的模型中。

回答by Vishal S Mujumdar

Short Version:

精简版：

1. Generate model with migration

   $ rails generate model Car vendor:references name:string ...

2. Add following line in Carmodel i.e car.rbfile

   class Car < ActiveRecord::Base
     belongs_to :company, :class_name => 'Vendor', :foreign_key => 'vendor_id'
   end
   

3. Now you have @car.companyinstance method.

1. 使用迁移生成模型

   $ rails generate model Car vendor:references name:string ...

2. 在Car模型 iecar.rb文件中添加以下行

   class Car < ActiveRecord::Base
     belongs_to :company, :class_name => 'Vendor', :foreign_key => 'vendor_id'
   end
   

3. 现在你有了@car.company实例方法。

For a Detailed explanation read ahead [Optional if you understood the above !!]

有关详细说明，请提前阅读[如果您理解上述内容，则可选！！]

Detailed Version:

详细版本：

The model Carwill have an association with the model Vendor(which is obvious). So there should be a vendor_idin the table cars.

模型Car将与模型有关联Vendor（这是显而易见的）。所以vendor_id表中应该有一个cars。

1. In order to make sure that the field vendor_idis present in the carstable run the following on the command line. This will generate the right migration. The vendor:referencesis important. You can have any number of attributes after that.

   $ rails generate model Car vendor:references name:string

2. Or else in the existing migration for create_table :carsjust add the line t.references :vendor

   class CreateCars < ActiveRecord::Migration
     def change
       create_table :cars do |t|
         t.string :name
         ...
         t.references :vendor
         t.timestamps
       end
     end
   end
   

3. The final thing that you need to do is edit the model Car. So add this code to your car.rbfile

   class Car < ActiveRecord::Base
     belongs_to :company, :class_name => 'Vendor', :foreign_key => 'vendor_id'
   end
   

1. 为了确保该字段vendor_id存在于cars表中，请在命令行上运行以下命令。这将生成正确的迁移。该vendor:references是很重要的。之后您可以拥有任意数量的属性。

   $ rails generate model Car vendor:references name:string

2. 或者在现有迁移中create_table :cars添加行t.references :vendor

   class CreateCars < ActiveRecord::Migration
     def change
       create_table :cars do |t|
         t.string :name
         ...
         t.references :vendor
         t.timestamps
       end
     end
   end
   

3. 您需要做的最后一件事是编辑模型Car。所以将此代码添加到您的car.rb文件中

   class Car < ActiveRecord::Base
     belongs_to :company, :class_name => 'Vendor', :foreign_key => 'vendor_id'
   end
   

After you do the third step you will get the following instance methods for the model Carprovided by Rails Associations

做完第三步之后，你会得到以下CarRails Associations提供的模型的实例方法

1. @car.company

   • When you do @car.companyit will return a #<Vendor ...>object. To find that #<Vendor ...>object it will go look for the vendor_idcolumn in the carstable because you have mentioned :foreign_key => 'vendor_id'

   • You can set the company for a car instance by writing

     @car.company = @vendor || Vendor.find(params[:id]) #whichever Vendor object you want
     @car.save
     

     This will save the idof that Vendorobject in the vendor_idfield of the carstable.

1. @car.company

   • 当你这样做时，@car.company它会返回一个#<Vendor ...>对象。要找到该#<Vendor ...>对象，它将查找表中的vendor_id列，cars因为您已经提到:foreign_key => 'vendor_id'

   • 您可以通过编写为汽车实例设置公司

     @car.company = @vendor || Vendor.find(params[:id]) #whichever Vendor object you want
     @car.save
     

     这将节省的id那的Vendor对象在vendor_id该领域cars表。

Thank You.

谢谢你。

回答by nickcen

class Car < ActiveRecord::Base
  belongs_to :vendor
  belongs_to :company, :class_name => :Vendor
end