如何在 Rails 中将多个 Rails SQL 查询组合成一个查询？

Question

在我的 rails 代码中，我需要根据记录日期和记录收到的投票的组合对表运行查询。我在 rails 中像下面这样完成它：

if params[:sort_by] == "default"
    objs1 = class_name.where("created_at between '#{Date.today - 7}' and '#{Date.today}' and net_votes > 0").order("net_votes DESC")
    objs2 = class_name.where("created_at between '#{Date.today - 30}' and '#{Date.today - 7}' and net_votes > 0").order("net_votes DESC")
    objs3 = class_name.where("created_at between '#{Date.today - 90}' and '#{Date.today - 30}' and net_votes > 0").order("net_votes DESC")
    objs4 = class_name.where("created_at < '#{Date.today - 90}' and net_votes > 0").order("net_votes DESC")
    objs = objs1 + objs2 + objs3 + objs4

抛开效率不谈，我不能在组合查询结果上使用分页，更不用说代码非常难看。这样做的正确方法是什么？

提前致谢。

Answer 1

使用order 进行排序逻辑，而不是where：

order_by_sql = <<-SQL
CASE WHEN created_at between '#{Date.today - 7}' and '#{Date.today}' THEN 1
     WHEN created_at between '#{Date.today - 30}' and '#{Date.today - 7}' THEN 2
     WHEN created_at between '#{Date.today - 90}' and '#{Date.today - 30}' THEN 3
     ELSE 4
END
SQL

objs = class_name.where('net_votes > 0').order(order_by_sql)

Answer 2

您可以做一些事情来使它更优雅并表现更好：

1) 将每个条件封装到一个作用域中。例如，net_vtoes > 0 是可重用的：

def self.has_votes
  where("net_votes > 0")
end

def self.ordered 
  order("net_votes DESC")
end

def self.last_week
  where("created_at between '#{Date.today - 7}' and '#{Date.today}'")
end

2) 按照 Ryan Bates 在此 RailsCast 中的建议创建一个范围运算符，以允许您以 OR 方式组合 where 条件：http://railscasts.com/episodes/355-hacking-with-arel?view=asciicast。这将让你构建一个这样的语句：

(MyClass.last_week | MyClass.last_month).has_votes.ordered