Make the rails enum integration aware of the original type

[willcosgrove]

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This change makes the :literal_enum attribute type, type-aware of the attribute that it is replacing.

Additionally it adds a literal_enum macro to ActiveRecord::Base that delegates to attribute and figures out the underlying attribute type.

My concern here is with calling type_for_attribute at class evaluation time is going to trigger a connection to the DB. This change broke my reproduction script because I created the database after defining the model. But this change makes the model definition require the database to be set up already.

Unfortunately I don't think we can lazy evaluate the type_for_attribute because after the call to attribute it's type will have changed to :literal_enum.

[ixti]

That's awesome! would be super awesome if literal_enum will actually work similar to enum:

class MyEnum < Literal::Enum(Integer)
  Foo = new(1)
  Bar = new(2)
end

class Example < ApplicationRecord
  literal_enum :x, MyEnum, suffix: true, validate: { allow_nil: true }
end

My current problem is that, when I use something like:

    def literal_enum(name, literal_enum, **)
      mapping = literal_enum.to_h do |o|
        [literal_enum.names.fetch(o).to_s.underscore, o.value]
      end

      enum(name, mapping, **)
    end

I get Rails enum good parts like: example.foo?, or Example.bar.to_a; but loose ability to get underlying value in a good way. I can live without those scopes and stuff, but I want model to be validateble, so that when wrong value passed - I can show an error.