从父类继承类定义 [英] Inheriting class definition from parent class

问题描述

我正在Rails模型中构建葡萄实体，如下所述:

I am building Grape Entities inside my Rails models as described here:

https://github.com/ruby-grape/grape-entity #entity-organization

目前，我正在根据模型本身的列哈希值自动创建默认值.

Currently I am creating default values automatically, based on the column hash of the model itself.

所以我有一个静态的get_entity方法，该方法公开了模型的所有列:

So I have a static get_entity method that exposes all the model's columns:

class ApplicationRecord < ActiveRecord::Base

  def self.get_entity(target)
    self.columns_hash.each do |name, column|
      target.expose name, documentation: { desc: "Col #{name} of #{self.to_s}" }
    end
  end

end

然后在这里有一个示例Book模型，在已声明的Entity子类中使用它(注释也显示了如何覆盖模型列之一的文档):

And then I have here an example Book model using it inside the declared Entity subclass (the comment also shows how I can override the documentation of one of the model's column):

class Book < ActiveRecord::Base

  class Entity < Grape::Entity
    Book::get_entity(self)
    # expose :some_column, documentation: {desc: "this is an override"}
  end

end

这种方法的缺点是，我总是需要在要为其创建实体的每个模型中复制并粘贴类Entity声明.

The downside with this approach is that I always need to copy and paste the class Entity declaration in each model I want the Entity for.

有人可以帮我为ApplicationRecord的所有子代自动生成类Entity吗?然后，如果需要重写，则需要在类中具有Entity声明，否则，如果默认声明足够并且可以保留原样.

Can anybody help me out generating the class Entity for all child of ApplicationRecord automagically? Then if I need overrides I will need to have the Entity declaration in the class, otherwise if the default declaration is enough and can leave it as it is.

注意:

我不能直接在ApplicationRecord内部添加类Entity定义，因为Entity类应调用get_entity，而get_entity取决于Books的column_hash.

I cannot add class Entity definition straight inside ApplicationRecord because, Entity class should call get_entity and get_entity depends on column_hash of Books.

解决方案:

由于脑袋而结束了这项工作:

ended up doing this thanks to brainbag:

def self.inherited(subclass)
  super
  # definition of Entity
  entity = Class.new(Grape::Entity)
  entity.class_eval do
    subclass.get_entity(entity)
  end
  subclass.const_set "Entity", entity

  # definition of EntityList
  entity_list = Class.new(Grape::Entity)
  entity_list.class_eval do
    expose :items, with: subclass::Entity
    expose :meta, with: V1::Entities::Meta
  end
  subclass.const_set "EntityList", entity_list
end

def self.get_entity(entity)
  model = self
  model.columns_hash.each do |name, column|
    entity.expose name, documentation: { type: "#{V1::Base::get_grape_type(column.type)}", desc: "The column #{name} of the #{model.to_s.underscore.humanize.downcase}" }
  end
end

谢谢！

推荐答案

我没有使用Grape，所以这里可能有一些我不知道的额外魔术，但这在Ruby中很容易做到/路轨.根据您的问题自动为ApplicationRecord的所有子类生成类Entity"，您可以执行以下操作:

I haven't used Grape so there may be some extra magic here that you need that I don't know about, but this is easy to do in Ruby/Rails. Based on your question "generating the class Entity for all child of ApplicationRecord automagically" you can do this:

class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true

  class Entity < Grape::Entity
    # whatever shared stuff you want
  end
end

然后图书将可以访问父级Entity:

Book will then have access to the parent Entity:

> Book::Entity
=> ApplicationRecord::Entity

如果只想向Book::Entity添加额外的代码，则可以在Book中将其子类化，如下所示:

If you want to add extra code only to the Book::Entity, you can subclass it in Book, like this:

class Book < ApplicationRecord
  class Entity < Entity # subclasses the parent Entity, don't forget this
    # whatever Book-specific stuff you want
  end
end

然后Book::Entity将是其自己的类.

> Book::Entity
=> Book::Entity

---

要将此与需要在继承的类上调用get_entity的需求相结合，可以使用#inherited方法在ApplicationRecord被子类化的任何时间自动调用get_entity:

---

To combine this with your need for get_entity to be called on an inherited class, you can use the #inherited method to automatically call get_entity any time ApplicationRecord is subclassed:

class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true

  def self.get_entity(target)
    target.columns_hash.each do |name, column|
      target.expose name, documentation: { desc: "Col #{name} of #{self.to_s}" }
    end
  end

  def self.inherited(subclass)
    super
    get_entity(subclass)
  end

  class Entity < Grape::Entity
    # whatever shared stuff you want
  end
end

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