当没有数据存在时,Sqldatareader'无效尝试读取' [英] Sqldatareader 'invalid attempt to read when no data is present'
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问题描述
我在asp.net项目中使用Visual Studio 2015企业版,其中我收到错误
I am using Visual Studio 2015 Enterprise edition for asp.net project in which i am getting error "
Invalid attempt to read when no data is present
实际上SqlDataReader正在执行命令但我得到这个错误可以有人解释我哪里错了
< b>我尝试过:
"
Actually the SqlDataReader is executing the command but i am getting this error can anyone explain me where is the wrong
What I have tried:
con = new SqlConnection(ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString);
if (con.State == ConnectionState.Closed)
con.Open();
string str = "select RoleName from tblRoles";
cmd = new SqlCommand(str, con);
sdr = cmd.ExecuteReader();
string roleName = sdr["RoleName"].ToString();
我收到错误最后一行说'无数据存在时读取无效'
I am getting error at the last line saying 'Invalid attempt to read when no data is present'
推荐答案
要使用DataReader,您必须告诉它一次读取每一行:
To use a DataReader, you have to tell it to read each line at a time:
using (SqlConnection con = new SqlConnection(strConnect))
{
con.Open();
using (SqlCommand cmd = new SqlCommand("SELECT RoleName FROM tblRoles", con))
{
using (SqlDataReader reader = cmd.ExecuteReader())
{
while (reader.Read())
{
string roleName = (string) reader["RoleName"];
Console.WriteLine(roleName);
}
}
}
}
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