导轨 - 添加自定义字段在运行时的ActiveRecord [英] Rails - Adding Custom Fields at runtime in ActiveRecord

问题描述

您知道一些bug跟踪系统（以及其他软件）如何让你添加自定义字段？

You know how some bug trackers (and other software) allow you to add custom fields?

通常这是一个数据结构，看起来像这样完成的：

Typically this is done with a data structure that looks something like this:

  Items
----------
 ID | NAME | ITEM_TYPE_ID


 FieldDefinitions
---------------------------------------
 ID | ITEM_TYPE_ID | FIELD_NAME | FIELD_TYPE

 FieldValues
---------------------------------------
ID | FIELD_ID | ITEM_ID | VALUE

我试图找出处理这个设计的Rails的最佳途径。将有很多车型，我想允许扩展简单的属性。

I'm trying to figure out the best way to approach this design in Rails. There will be many models which I want to allow extending simple properties.

当我retreive一个项目我想它包括已被定义为模型添加字段值的哈希值。

When I retreive an Item I'd like it to include a hash of the addition field values that have been defined for that model.

推荐答案

喜欢的东西...？

class Item < ActiveRecord::Base
  has_many :field_values
  has_many :field_definitions, :through => :field_values

  def custom_fields_hash
    cfh = {}
    self.field_values.each |fv|
      cfh[fv.field_definition] = fv
    end
    cfh
  end
end

class FieldValue < ActiveRecord::Base
  belongs_to :item
  belongs_to :field_definition
end

class FieldDefinition < ActiveRecord::Base
  has_many :field_values
  has_many :items, :through => field_values
end

或者，你可以改变

Or, you could change

cfh[fv.field_definition] = fv

...到...

...to...

cfh[fv.field_definition.field_name] = fv.value

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