**修改为更好的可理解性** @H_404_2@**编辑重新命名为文档**

@H_404_2@我想用给定用户的投票记录获取所有用户的文档记录,如果该用户没有投票支持某些文档记录,我仍然希望得到所有的文档记录,而无需投票.
例如：

+------------+--------------+------+
|document.par1|document.par2| vote |
+------------+--------------+------+
|    2       | z            | y    |
|    3       | w            | NULL |
|    4       | x            | NULL |
+------------+--------------+------+

@H_404_2@在Ruby on Rails上,如果我尝试这样：

@H_404_2@冷杉试试：

Document.
   joins("LEFT JOIN `votes` ON `votes`.`v_id` = `document`.`id` AND `votes`.`giver_id` = ?",user_id).
   where('document.creator_id = ?',user_id,.....).
   select('votes.*',`document.param1')

@H_404_2@我收到这个错误：

RuntimeError in UserDocumentsController#show
 
unknown class: Fixnum

@H_404_2@II.第二尝试：

Document.
   joins("LEFT JOIN `votes` ON `votes`.`v_id` = `document`.`id`").
   where('document.creator_id = ? AND `votes`.`giver_id` = ?',`document.param1')

@H_404_2@仅返回有投票记录：

+-------------+-------------+------+
|document.par1|document.par2| vote |
+-------------+-------------+------+
|    2        | z           | y    |
+-------------+-------------+------+

@H_404_2@所以没有2条记录..

@H_404_2@**更新,此解决方案工作**

@H_404_2@III.我的第三个尝试,谢谢你的帮助Mischa：

Document.
   joins("LEFT JOIN `votes` ON `votes`.`v_id` = `document`.`id`").
   where('document.creator_id = ? AND (`votes`.`giver_id` = ? OR  `votes`.`giver_id` IS NULL)',user_id).
   select('votes.*',`document.param1')
 
+-------------+-------------+------+
|document.par1|document.par2| vote |
+-------------+-------------+------+
|    2        | z           | y    |
|    3        | w           | NULL |
|    4        | x           | NULL |
+-------------+-------------+------+

Document.
   joins("LEFT JOIN `votes` ON `votes`.`v_id` = `document`.`id`").
   where('document.creator_id = ? AND (`votes`.`giver_id` = ? OR  `votes`.`giver_id` IS NULL)',`document.param1')