Second attempt

avram_enum2.cr

module AvramEnumConstants
  module Lucky
    alias ColumnType = Int32
  end
end
module AvramEnum
  def self.adapter
    Lucky
  end
  module Lucky
    def from_db!(value : Int32)
      new(value)
    end

    def parse(value : String)
      from_value(value.to_i)
    end

    def parse(value : Int32)
      from_value(value)
    end

    def to_db(value : Int32)
      value.to_s
    end

    def to_db(value : Enum)
      value.value.to_s
    end
  end
end

struct Enum
  extend AvramEnum

  include AvramEnumConstants
end

model.cr

class MergeRequest < BaseModel
  enum Status
    Open = 0
    Closed = 1
    Merged = 2
  end

  table do
    column name : String
    column status : MergeRequest::Status
  end
end