问题描述
private void button1_Click(object sender, EventArgs e)
{
string name;
name = textBox5.Text;
SqlConnection con10 = new SqlConnection("con strn");
SqlCommand cmd10 = new SqlCommand("select * from sumant where username=@name");
cmd10.Parameters.AddWithValue("@name",name);
cmd10.Connection = con10;
cmd10.Connection.Open();//line 7
SqlDataReader dr = cmd10.ExecuteReader();
}
if ( textBox2.Text == dr[2].ToString())
{
//do something;
}
当我调试到第 7 行时，一切正常，但之后 dr 抛出异常:
When I debug until line 7, it is OK, but after that dr throws an exception:
不存在数据时尝试读取无效.
Invalid attempt to read when no data is present.
我不明白为什么会出现该异常，因为我的表中有用户名=sumant 的数据.
I don't understand why I'm getting that exception, since I do have data in the table with username=sumant.
请告诉我if"语句是否正确.以及如何修复错误?
Please tell me whether the 'if' statement is correct or not. And how do I fix the error?
推荐答案
你必须调用 DataReader.Read 获取结果:
You have to call DataReader.Read to fetch the result:
SqlDataReader dr = cmd10.ExecuteReader();
if (dr.Read())
{
// read data for first record here
}
DataReader.Read() 返回一个 bool 指示是否有更多的数据块要读取，所以如果你有超过 1 个结果，你可以这样做:
DataReader.Read() returns a bool indicating if there are more blocks of data to read, so if you have more than 1 result, you can do:
while (dr.Read())
{
// read data for each record here
}
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