Rails模型变量属性

Question

I have model Post, which belongs to Category, as usual, Post has several attributes (such as title:string, content:text, …).

The quantity of categories wouldn't be more than five (now there are only 3), so the question is: which is the best way to add some attributes based on Post's category. Eg if Post belongs to category_1, then it would have 2 more attributes (attr_1, attr_2), if Post belongs to category_2 then it would have initial attributes + 3 more (attr_3, attr_4, attr_5).

Should I "hardcode" this or it would be better to add field to Post model (eg JSON-like field additional_attributes)?

Example: 3 categories, 3 posts (one post in each category). Basically, post have 2 fields: title, text. But, if post is in category_1 it should also have rank and history, if post is in category_2 it should not have rank or history, but should have points.

Answer 1

I think this can be handled nice if you just add all the possible attributes to the Post model and create conditional validators (depending on the Category).

class Post < ActiveRecord::Base
  # This is always validated
  validates :title, presence: true

  # Validation for Posts with category type1
  with_options if: Proc.new { |p| a.category.type == 'type1' } do |post|
    post.validates :rank, length: { minimum: 10 }
    post.validates :history, presence: true
  end

  # Validation for Posts with category type2
  with_options if: Proc.new { |p| a.category.type == 'type2' } do |post|
    post.validates :extra_field, length: { maximum: 20 }
    post.validates :points, presence: true
  end
end

You should adapt the way you determine what type of category you are dealing with to your own needs.