Typecasting base class models in Single Table Inheritence(STI) scenario

Question

class User < ActiveRecord::Base   
end  

class Consumer < User 
end  

class Merchant < User 
end   

u = User.find(id)

How do I type cast the variable u to the type Consumer?

Answer 1

You need a column called 'type' and rails will do the rest. For example:

id = Consumer.create!(...).id

# later on

User.find(id).is_a? Consumer  # ==> true

Answer 2

I found the answer to this. The ActiveRecord::Base class has a method for this purpose:

http://api.rubyonrails.org/classes/ActiveRecord/Base.html#M002334

The code will be

u = User.find(id)
u = u.becomes(u.type.constantize)

Answer 3

Due to a bug in STI, the ActiveRecord finder was returning a base class instance(User) instead of subclass instance(Consumer). I thought this is the default behavior and hence wanted to cast the base class instance(User) to the sub class instance(Consumer). My previous solution became redundant after addressing the bug. i.e.

u = User.find(id) # returns an instance of Consumer class

Answer 4

You can always get a Consumer as such:

u = Consumer.find(id)