Ruby on Rails 3中的模型继承

Question

Please help a newbie to choose the best way to implement inheritance in RoR3. I have:

-Person (address fields, birthdate, etc.)
   -Player, inherits from Person (position, shoe_size, etc.)
      -Goalkeeper, inherits from Player (other specific fields related to this role)

I think that Single Table Inheritance is a bad solution, because there will be a lot of null fields in the table created. What is the best way to do this? Use polymorphic associations (with has_one?)? Use belongs_to/has_one (but then how to show in the Player views the fields of Person too?)? Don't implement inheritance? Other solutions?

Answer 1

While I think STI is probably the approach I would use for this, one other possibility, if you want to avoid a lot of NULL attributes, is to add a column other_attributes to your Person model that will store a Hash of attributes. To do this, add a text column to the people table:

def self.up
  add_column :people, :other_attributes, :text
end 

Then make sure the attribute is serialized in the model. And you may want to write a wrapper to make sure it's initialized as an empty Hash when you use it:

class Person < ActiveRecord::Base
  serialize :other_attributes

  ...

  def other_attributes
    write_attribute(:other_attributes, {}) unless read_attribute(:other_attributes)
    read_attribute(:other_attributes)
  end
end

Then you can use the attribute as follows:

p = Person.new(...)
p.other_attributes                          #=> {}
pl = Player.new(...)
pl.other_attributes["position"] = "forward"
pl.other_attributes                         #=> {"position" => "forward"}

One caveat with this approach is that you should use strings as keys when retrieving data from other_attributes , as the keys will always be strings when the Hash is retrieved from the database.

Answer 2

I suggest STI. An alternative solution is to use a document store like mongodb, or use the activerecord store http://api.rubyonrails.org/classes/ActiveRecord/Store.html . If you have a postgress database look at his HStore column http://rubygems.org/gems/activerecord-postgres-hstore .

Another option is PostgreSQL table inheritance. http://www.postgresql.org/docs/8.1/static/ddl-inherit.html