英文:
Invalid memory address or nil pointer dereference when database returns empty set
问题
当我将事件ID传递给DisplayScanMembers(23)时，如果数据库中不存在该event_id，它将返回一个空集。然而，显然一个空集等同于一个空指针（我猜）。因此，我无法将值（空指针）赋给DisplayScanMembers函数中的'member_s'。
我只需要getScanMembers方法在数据库查询返回空集时返回一个空数组，而不是空指针。
我得到的错误信息：
ERROR 2014/10/22 23:08:19 panic.go:29: runtime error: invalid memory address or nil pointer dereference
/home/developer/gocode/src/drakecheckin/app/controllers/scan.go:236 (0x4a21f8)
func (c Scan) DisplayScanMembers(id int64) revel.Result{if (id == -1 || id == 0){event,_ :=c.getLatestSelectedEvent();member_s,_ := c.getScanMembers(event.EventId);return members;} else {member_s,err2 := c.getScanMembers(id);if err2 !=nil {event,_ :=c.getLatestSelectedEvent();member_s,_ = c.getScanMembers(event.EventId);}return member_s;}}func (c Scan) getScanMembers(event_id int64) (revel.Result,error) {group_id,_ := convStrInt(c.Session["group_id"]);org_id,_ := convStrInt(c.Session["org_id"]);;query := "SELECT me.member_event_id,m.member_first_name,m.member_last_name,m.member_uniq_num "+"FROM MemberEvent AS me JOIN Member AS m ON m.member_id =me.member_id AND m.org_id =me.org_id "+"WHERE me.group_id=? AND me.org_id=? AND me.event_id=?";members, err := c.Txn.Select(models.AllMemberEvent{}, query, group_id, org_id, event_id);if err != nil {return nil,err;}return c.RenderJson(members),nil;}
英文:
When I pass event id in to DisplayScanMembers(23), if the event_id does not appear in the database, it returns an empty set. However, apparently an empty set is equivalent a nil pointer(I guess). Therefore I cannot assign the value(nil pointer) to 'member_s' in the DisplayScanMembers function.
All I need is for the getScanMembers method to return an empty array instead nil if the database query returns a empty set.
Error that I get:
ERROR 2014/10/22 23:08:19 panic.go:29: runtime error: invalid memory address or nil pointer dereference
/home/developer/gocode/src/drakecheckin/app/controllers/scan.go:236 (0x4a21f8)
func (c Scan) DisplayScanMembers(id int64) revel.Result{if (id == -1 || id == 0){event,_ :=c.getLatestSelectedEvent();member_s,_ := c.getScanMembers(event.EventId);return members;} else {member_s,err2 := c.getScanMembers(id);if err2 !=nil {event,_ :=c.getLatestSelectedEvent();member_s,_ = c.getScanMembers(event.EventId);}return member_s;}}func (c Scan) getScanMembers(event_id int64) (revel.Result,error) {group_id,_ := convStrInt(c.Session["group_id"]);org_id,_ := convStrInt(c.Session["org_id"]);;query := "SELECT me.member_event_id,m.member_first_name,m.member_last_name,m.member_uniq_num "+"FROM MemberEvent AS me JOIN Member AS m ON m.member_id =me.member_id AND m.org_id =me.org_id "+"WHERE me.group_id=? AND me.org_id=? AND me.event_id=?";members, err := c.Txn.Select(models.AllMemberEvent{}, query, group_id, org_id, event_id);if err != nil {return nil,err;}return c.RenderJson(members),nil;}
答案1
得分: 1
我认为你的问题在于"getScanMembers"函数。你的返回语句是revel.Result，如果有错误，你这样处理：
if err != nil {return nil, err;}
但是你应该这样处理：
if err != nil {return revel.Result{}, err;}
英文:
I think your problem in "getScanMembers" function. Your return statement is revel.Result, and if you have error, you doing this:
if err != nil {return nil, err;}
But you should doing this:
if err != nil {return revel.Result{}, err;}
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