Single Table Inheritance - Additional Class Name

Question

I have a situation in my Rails 4 app, where I have STI and want to customize the default queries by additional type.

Classes:

class Candidate < ApplicationRecord
end

class Candidate::Site < Candidate
end

Now, if I make query, I get results as follow:

> Candidate::Site.count
# SELECT COUNT(*) FROM "candidates" WHERE "candidates"."type" IN ('Candidate::Site')
=> 0

Now, in my situation, I want to add an additional type which query should look for every time. By leveraging the IN clause, my expected query to be fired is:

SELECT COUNT(*) FROM "candidates" WHERE "candidates"."type" IN ('Candidate::Site', 'Site')

Can someone help me out to control this IN clause here? Thanks in advance.

Answer 1

After detailed research and diving deep into the Rails STI source code, I found that my scenario will need to override the Rails' default STI. Following is what I needed to achieve the goal:

class Candidate::Site

  # To enable renaming of Site to Candidate::Site
  # per ENG-9551, we need to:
  # 1. disable the 'type' column from using Rails' built-in STI
  self.inheritance_column = :_nonexistant_column_to_bypass_sti

  # 2. manually set the type column to Candidate::Site when we save,
  # so that new and edited records are saved as Candidate::Site
  before_save { self.type = 'Candidate::Site' }

  # 3. always report the type as a Candidate::Site
  def type
    'Candidate::Site'
  end

  # 4. and set a default scope which only reads type columns that are
  # 'Candidate::Site' or 'Site' so that STI
  # still appears to be the same as always
  default_scope { where(type: 'Candidate::Site').or(where(type: 'Site')) }

  ...
  ...
  ...
end

So, now any new record created with Candidate::Site.create will store type Candidate::Site while queries will use default scope and consider both the type, Candidate::Site as well as Site.