修正軌道

Question

的MySQL查詢在執行中軌下方MySQL查詢

cnt = Domainurl.find_by_sql ["SELECT Max(`count`)FROM `domainurls` WHERE `domaindetail_id`= ?",@domain.id] 
urlcr=Domainurl.find_by_sql ["SELECT * FROM `domainurls` WHERE `domaindetail_id` = ? AND `count` = ?",cnt.count] 
urlcr.each do |cr| 
    puts cr.url 
end 

我得到錯誤：

"error is: undefined method `closed?' for nil:NilClass" 

我有點在MySQL弱，任何人都可以指導我糾正我的錯？ :)

謝謝:)

Answer 1

問題是你的最後一個查詢

urlcr=Domainurl.find_by_sql ["SELECT * FROM `domainurls` WHERE `domaindetail_id` = ? AND `count` = ?",cnt.count] 

嘗試找到2個參數（domaindetail_id和count）的東西，但你只提供count。 （您必須提供domaindetail_id太）

urlcr=Domainurl.find_by_sql ["SELECT * FROM `domainurls` WHERE `domaindetail_id` = ? AND `count` = ?",@domain.id, cnt.count] #observe that I added @domain.id 

可以重寫，像

cnt = Domainurl.where(:domaindetail_id => @domain.id).maximum(:count) # this returns a number 
urlcr=Domainurl.where("domaindetail_id = ? AND count = ?", @domain.id, cnt)