Error if reader.read !=Null

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How do I catch an empty reader.read an exception?

C#

private void KlantenContactInfo()
{
    const string queryKlantContactinfoID = "SELECT Naam, Telefoonnummer, Mobiel, Mail FROM KlantenContact WHERE IDKlantContactpersonen = @SELKlantcontactinfoID";

    using (SqlConnection connection = new SqlConnection(connectionstring))
    using (SqlCommand command = new SqlCommand(queryKlantContactinfoID, connection))
    {
        if (ListBoxKlanten.Items.Count == 0)
        {
            command.Parameters.AddWithValue("@SELKlantcontactinfoID", DBNull.Value);
        }
        else
        {
            command.Parameters.AddWithValue("@SELKlantcontactinfoID", listBoxKlantenContact.SelectedValue);
        }

        connection.Open();
        using (SqlDataReader reader = command.ExecuteReader(CommandBehavior.CloseConnection | CommandBehavior.SingleResult | CommandBehavior.SingleRow))
        {
            //HELP
            if (reader.Read())
            {
                LB_KlantenContactNaam.Text = Convert.ToString(reader["Naam"]);
                LB_KlantenContactTelefoon.Text = Convert.ToString(reader["Telefoonnummer"]);
                LB_KlantenContactMobiel.Text = Convert.ToString(reader["Mobiel"]);
                LB_KlantenContactMail.Text = Convert.ToString(reader["Mail"]);
            }
        }
    }
}

Posted 15-Dec-15 23:30pm

MaikelO1

Updated 15-Dec-15 23:35pm

phil.o

v2

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Jörgen Andersson · Answer 1 · 2015-12-16T03:19:00

Your test:

C#

if (ListBoxKlanten.Items.Count == 0)

is insufficient.
In this case it's apparent that listBoxKlantenContact has values, but none is selected so listBoxKlantenContact.SelectedValue is null.

Try using

C#

command.Parameters.AddWithValue("@SELKlantcontactinfoID", listBoxKlantenContact.SelectedValue ?? DBNull.Value);

phil.o · Answer 2 · 2015-12-15T23:36:00

Solution 1

Try

C#

while (reader.Read()) {
   // ...
}

instead of

C#

if (reader.Read()) {
   // ...
}

Hope this helps.

Posted 15-Dec-15 23:36pm

phil.o

Comments

MaikelO1 16-Dec-15 5:47am

I already tried that. That is not the solution. Attached a screenshot of my fault that I get if ListBoxKlanten.Items.Count >1 and there are no results in reader.read ..

http://s4.postimg.org/fnstvloe5/Screen_Shot_2015_12_16_at_11_40_48.jpg

phil.o 16-Dec-15 6:03am

Have you read the exception message to the right of the image? It is clearly descriptive.

Foothill · Answer 3 · 2015-12-16T09:23:00

Solution 3

Try

C#

if (reader.HasRows)
{
  reader.Read();
  //...
}

Or, the round-about way

C#

// In the SqlDataReader using block
using (DataTable results = new DataTable())
{
  results.Load(reader);
  if (results.Rows.Count > 0)
  {
    // map results to your fields
  }
}

Posted 16-Dec-15 9:23am

Foothill

Updated 16-Dec-15 9:24am

v2