如何將多個Rails SQL查詢合併到一個單獨的查詢中？

Question

在我的rails代碼中，我需要根據記錄的日期和記錄收到的投票的組合來對錶進行查詢。我完成它就像在軌道下面：

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 

效率不談，我不能在組合查詢結果使用分頁更不用說代碼是非常難看。什麼是正確的方法來做到這一點？

在此先感謝。

Answer 1

的排序邏輯使用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

有幾件事情可以做，以使這更優雅和有更好的表現：每個條件

1）封裝成範圍。例如，net_vtoes> 0是可重複使用：

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）創建一個範圍運算符，由Ryan貝茨在此RailsCast建議，讓您可以結合其中一個或時裝條件：http://railscasts.com/episodes/355-hacking-with-arel?view=asciicast。這會讓你建立一個這樣的陳述：

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