Get a list/array of child classes from Single Table Inheritance in Rails?

Question

I have a whole bunch of child classes that inherit from a parent class via single-table-inheritance in my Rails app. I\'d like a way to get an array of all the child classes tha

Answer 1

In your config/environments/development.rb

Rails.application.configure do
  config.eager_load = false
end

U can change false to true, and then in your console to do

Class.subclasses

or

Class. descendants

here is the difference between subclasses and descendants

subclasses:

class Foo; end
class Bar < Foo; end
class Baz < Bar; end

Foo.subclasses # => [Bar]

descendants:

class C; end
C.descendants # => []

class B < C; end
C.descendants # => [B]

class A < B; end
C.descendants # => [B, A]

class D < C; end
C.descendants # => [B, A, D]

Answer 2

ParentClass.subclasses.map(&:name)

Answer 3

This will do it in one SQL query:

# SELECT DISTINCT type FROM objects
Object.uniq.pluck(:type)

Answer 4

You need to eager load the classes, as stated in: https://github.com/rails/rails/issues/3364

ActionDispatch::Reloader.to_prepare do
  Rails.application.eager_load!
end

Then you will be able to use:

YourClass.subclasses

or

YourClass.descendants

Answer 5

Note, their is a more efficient way to implement Dave G's method above..

Object.select(:type).map(&:type).uniq

This first sends marshaled objects that only have the "type" attribute from the DB, which takes WAY less memory, then plucks only the types into an array that you can then uniq on. I'm sure there is an infinitely more efficient pure SQL way to do this though.

Answer 6

Assuming there is at least one of each of object extant in the table:

Object.all.uniq{|x| x.type}.collect(&:type)