如何将多个Rails SQL查询合并到一个单独的查询中？

Question

在我的rails代码中，我需要根据记录的日期和记录收到的投票的组合来对表进行查询。我完成它就像在轨道下面：

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 

效率不谈，我不能在组合查询结果使用分页更不用说代码是非常难看。什么是正确的方法来做到这一点？

在此先感谢。

Answer 1

的排序逻辑使用order，不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

有几件事情可以做，以使这更优雅和有更好的表现：每个条件

1）封装成范围。例如，net_vtoes> 0是可重复使用：

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）创建一个范围运算符，由Ryan贝茨在此RailsCast建议，让您可以结合其中一个或时装条件：http://railscasts.com/episodes/355-hacking-with-arel?view=asciicast。这会让你建立一个这样的陈述：

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