How to check if SQLDataReader has no rows

问题

I am trying to figure out how to check if my SqlDataReader is null or has no rows (meaning the reservation does not exist) and then display a messagebox. For some reason when I debug once it hits the While dr.Read()) code it steps out if it does not have a return result.

I've tried putting this code in a few different locations but none seem to fire off the messagebox if no records are returned

if (dr.GetValue(0) == DBNull.Value || !dr.HasRows)
{
    MessageBox.Show("Reservation Number Does Not Exist","Error", MessageBoxButtons.OK, MessageBoxIcon.Asterisk);
}
else
{
    (read records)
}

My code...

try
{
   using (SqlConnection con = new SqlConnection(connectionString))
   {
      using (SqlCommand cmd = con.CreateCommand())
      {
         con.Open();
         cmd.CommandText = "usp_StoredProcedureName";
         cmd.CommandType = CommandType.StoredProcedure;
         cmd.Parameters.AddWithValue("@regnum", regnumber);

         using (SqlDataReader dr = cmd.ExecuteReader())
         {
             //Loop through all the rows, retrieving the columns you need.
             while (dr.Read())
             {
                 lblConf.Text = dr.GetValue(0).ToString();
                 lblName.Text = dr.GetValue(1).ToString() + "," + dr.GetValue(2);
                 lblCompany.Text = dr.GetValue(3).ToString();
                 lblStatus.Text = dr.GetValue(4).ToString();
             }
         }
      }
   }
}
catch (Exception ex)
{
    MessageBox.Show("Can not open connection! ");
}

回答1:

if(dr.HasRows)
{
    // ....
}
else
{
    MessageBox.Show("Reservation Number Does Not Exist","Error", MessageBoxButtons.OK, MessageBoxIcon.Asterisk);
}

SqlDataReader.HasRows Property

回答2:

Add this to your code to check:

sqlCommand cmd = new sqlCommand();
SqlDataReader dr = cmd.ExecuteReader();

if(dr.HasRows)
{
    while(dr.Read())
    {
        //code
    }
}

回答3:

The HasRows property may help you.

Property Value

Type: System.Boolean true if the SqlDataReader contains one or more rows; otherwise false.

回答4:

For some reason when I debug once it hits the while dr.Read() Code it steps out if it does not have a return result

I think what you're seeing here is that SQLDataReader.Read() returns false if there is not a next, or in this case a first record to read.

As others have responded, use the HasRows property to determine if you have any rows in the result set. Depending on what you need to accomplish, you may want to take advantage of the fact that Read() indeed returns false the first time its called for an empty result set.

来源：https://stackoverflow.com/questions/12609959/how-to-check-if-sqldatareader-has-no-rows

标签

sqldatareader