class FixHogeTables < ActiveRecord::Migration[5.1]
  def change
    table(:hoges).where(type: 'bar').each do |hoge|
      ...
    end
  end

  def table(name)
    result = Class.new(ActiveRecord::Base) do
      self.table_name = name
      self.inheritance_column = :_dummy_column
    end
    result.reset_column_information
    result
  end
end