Rails的多态的has_many

问题描述

使用Ruby on Rails，我怎么能实现多态的has_many 关系，其中的主人始终是一个已知的，但在协会的项目会出现一些多态的（但同质的）类型，由车主一栏规定？例如，假设在监制类的has_many 产品，但生产情况实际上可能有许多自行车，或冰棍，或鞋带。我可以很容易地让每个产品类别（自行车，冰棒等）有一个监制一个 belongs_to的关系，但由于制片比如我怎样才能得到，如果他们的产品集合有不同的类型（每生产实例）的？

Using Ruby on Rails, how can I achieve a polymorphic has_many relationship where the owner is always of a known but the items in the association will be of some polymorphic (but homogenous) type, specified by a column in the owner? For example, suppose the Producer class has_many products but producer instances might actually have many Bicycles, or Popsicles, or Shoelaces. I can easily have each product class (Bicycle, Popsicle, etc.) have a belongs_to relationship to a Producer but given a producer instance how can I get the collection of products if they are of varying types (per producer instance)?

Rails的多态关联允许生产者属于许多产品，但我需要的关系是周围的其他方式。例如：

Rails polymorphic associations allow producers to belong to many products, but I need the relationship to be the other way around. For example:

class Bicycle < ActiveRecord::Base
  belongs_to :producer
end

class Popsicle < ActiveRecord::Base
  belongs_to :producer
end

class Producer < ActiveRecord::Base
  has_many :products, :polymorphic_column => :type # last part is made-up...
end

所以，我的制片人表已有对应于某些产品类别（如自行车，冰棒等），但我怎么能得到的Rails让我像做一个类型列：

So my Producer table already has a "type" column which corresponds to some product class (e.g. Bicycle, Popsicle, etc.) but how can I get Rails to let me do something like:

>> bike_producer.products
#=> [Bicycle@123, Bicycle@456, ...]
>> popsicle_producer.products
#=> [Popsicle@321, Popsicle@654, ...]

如果这是显而易见的，或一个共同的重复对不起;我有令人惊讶的困难很容易实现的。

Sorry if this is obvious or a common repeat; I'm having surprising difficulty achieving it easily.

推荐答案

下面是我目前使用的解决方法。它不提供任何你从真正的ActiveRecord ::协会得到方便的方法（收集操作），但它确实提供了一种方式来获得产品列表给定生成：

Here is the workaround I'm currently using. It doesn't provide any of the convenience methods (collection operations) that you get from real ActiveRecord::Associations, but it does provide a way to get the list of products for a given producer:

class Bicycle < ActiveRecord::Base
  belongs_to :producer
end

class Popsicle < ActiveRecord::Base
  belongs_to :producer
end

class Producer < ActiveRecord::Base
  PRODUCT_TYPE_MAPPING = {
    'bicycle' => Bicycle,
    'popsicle' => Popsicle
  }.freeze
  def products
    klass = PRODUCT_TYPE_MAPPING[self.type]
    klass ? klass.find_all_by_producer_id(self.id) : []
  end
end

另一个缺点是，我必须保持字符串类型的映射键入类，但是，可以实现自动化。然而，这种解决方案就足够了，我的目的

Another downside is that I must maintain the mapping of type strings to type classes but that could be automated. However, this solution will suffice for my purposes.

这篇关于Rails的多态的has_many的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！