Ch 14 adapter.Fill and ExecuteNonQuery

comecme · December 7th, 2010, 03:47 AM

Hi DrPurdum,

In Listing 14-9 in the book, in method DoQuery(), you have the following code:

Code:

try
{
 ds = newDataSet(); // Instantiate DataSet object
 conn.Open();
 command.CommandText = txtQuery.Text;
 adapter = newOleDbDataAdapter(command);
 adapter.Fill(ds);
 dataGridView1.DataSource = ds.Tables[0];
 command.ExecuteNonQuery();
}
catch (Exception ex)
{
 MessageBox.Show("Error: " + ex.Message);
}
finally
{
 conn.Close();
}

I wonder why you use the command.ExecuteNonQuery() statement. As far as I can tell, the adapter.Fill(ds) already executes the SQL statement and fills the dataset.

In the book, you say that the call to Fill just passes the dataset and the ExecuteNonQuery executes the actual query. That is not what I see when debugging the code. Once the Fill has been executed, the DataSet contains a table with several rows in it.

DrPurdum · December 8th, 2010, 12:36 AM

It's been almost three years since I wrote that code, but the call to ExecuteNonQuery() is not needed for what the code does. My guess is that I had something in mind for later use in the code, but decided not to put it in and just left the call in. It's not an editor mistake, as my original code had it in there, too. Not sure what I was thinking...

The ExecuteNonQuery() is often used to perform catalog operations or to change the data in a database without using a DataSet by executing UPDATE, INSERT, or DELETE statements. For those operations, the call returns the number of rows affected by the call.

Sorry for the confusion...