Question

我有以下用于搜索表格中文本的方法

protected void fillGridView(int followingID, string text)
    {

        SqlCommand myCommand = new SqlCommand("select t.*,u.firstName,u.lastName,u2.firstName as afirstName,u2.lastName as alastName ,i.icon,ii.iconPath as taskIcon, iii.iconPath as seenIcon,f.fileName,f.fileID from tasks as t inner join users as u on u.userID=t.addedBy inner join users as u2 on u2.userID=t.attachTo inner join priorityIcons as i on t.priority=i.priorityID inner join icons as ii on t.status=ii.iconName inner join icons as iii on t.isNew=iii.iconName left join files as f on t.fileID=f.fileID where t.followingID=@followingID and t.firstName LIKE '%asd%'");


        myCommand.Parameters.AddWithValue("@followingID", followingID);
        myCommand.Parameters.AddWithValue("@text", text);            

        DBAccess db = new DBAccess();
        DataSet ds = db.select(myCommand);

        SqlDataAdapter adapter = new SqlDataAdapter();

        tasksRepeater.DataSourceID = null;
        tasksRepeater.DataSource = ds.Tables[0]; //Here the exception appear because the dataset ds is "null" 
        tasksRepeater.DataBind();
        tasksCounter();
    }

异常消息是“对象引用未设置为对象的实例。”

但是当我用上面的sql语句交换sql语句时，代码运行成功

SqlCommand myCommand = new SqlCommand("select t.*,u.firstName,u.lastName,u2.firstName as afirstName,u2.lastName as alastName ,i.icon,ii.iconPath as taskIcon, iii.iconPath as seenIcon,f.fileName,f.fileID from tasks as t inner join users as u on u.userID=t.addedBy inner join users as u2 on u2.userID=t.attachTo inner join priorityIcons as i on t.priority=i.priorityID inner join icons as ii on t.status=ii.iconName inner join icons as iii on t.isNew=iii.iconName left join files as f on t.fileID=f.fileID where t.followingID=@followingID");

那么问题是什么！？

Answer 1

您的查询未返回任何行，因此当您执行ds.Tables[0]时，它会抛出，因为ds.Tables为空。

我怀疑您的查询有拼写错误，因为您正在设置@text参数的值，但查询中不存在该参数。您的查询可能需要以：

结束

"...where t.followingID=@followingID and t.firstName LIKE '%@text%'"

话虽这么说，你的代码应该能够处理查询没有返回任何行的情况（你可以通过检查ds.Tables上的Count属性来检查这一点。）

Answer 2

我猜错误在where子句中。请尝试使用此查询

"select t.*,u.firstName,u.lastName,u2.firstName as afirstName,u2.lastName as alastName ,i.icon,ii.iconPath as taskIcon, iii.iconPath as seenIcon,f.fileName,f.fileID from tasks as t inner join users as u on u.userID=t.addedBy inner join users as u2 on u2.userID=t.attachTo inner join priorityIcons as i on t.priority=i.priorityID inner join icons as ii on t.status=ii.iconName inner join icons as iii on t.isNew=iii.iconName left join files as f on t.fileID=f.fileID where t.followingID=@followingID and u.firstName LIKE '%asd%'"

输入u.FirstName而不是t.firstName。

我猜错误是t的别名。

试试这个。

sql select语句出错

2 个答案: