ORDER BY IDS SEQUENCE

ORDER BY IDS SEQUENCE

1. Mysql only

> ids = [11,31,29]
=> [11, 31, 29]
> Page.where(id: ids).order("field(id, #{ids.join(',')})")

2. Postrgesql variant

  def self.order_by_ids(ids)
    order_by = ["case"]
    ids.each_with_index.map do |id, index|
      order_by << "WHEN id='#{id}' THEN #{index}"
    end
    order_by << "end"
    order(order_by.join(" "))
  end

  User.where(:id => [3,2,1]).order_by_ids([3,2,1]).map(&:id) 
    #=> [3,2,1]