无效的内存地址或空指针解引用,当数据库返回空集时。

huangapple go评论147阅读模式
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;
}

huangapple
  • 本文由 发表于 2014年10月23日 12:49:32
  • 转载请务必保留本文链接:https://go.coder-hub.com/26521490.html
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