Invalid attempt to read when no data is present

    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;
}

When I debug until line 7, it is OK, but after that dr throws an exception:

Invalid attempt to read when no data is present.

I don't understand why I'm getting that exception, since I do have data in the table with username=sumant.

Please tell me whether the 'if' statement is correct or not. And how do I fix the error?

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小开

You have to call dr.Read() before attempting to read any data. That method will return false if there is nothing to read.

小开

最佳答案

You have to call DataReader.Read() to fetch the result:

SqlDataReader dr = cmd10.ExecuteReader();
if (dr.Read())
{
// read data for single/first record here
}

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
}

小开

I would check to see if the SqlDataReader has rows returned first:

SqlDataReader dr = cmd10.ExecuteReader();
if (dr.HasRows)
{
...
}

小开

I just had this error, I was calling dr.NextResult() instead of dr.Read().

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I used the code below and it worked for me.

String email="";
SqlDataReader reader=cmd.ExecuteReader();
if(reader.Read()){
email=reader["Email"].ToString();
}


String To=email;

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I was having 2 values which could contain null values.

while(dr.Read())
{
Id = dr["Id"] as int? ?? default(int?);
Alt =  dr["Alt"].ToString() as string ?? default(string);
Name = dr["Name"].ToString()
}

resolved the issue