Visual Basic

Private Sub txtPaese_Leave_1(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txtPaese.Leave
    Try
        Using cn As New OdbcConnection("dsn=PHOENIXDB;uid=SYSDBA;pwd=masterkey;")
            
            ' TODO: Only select the columns you're going to use.
            Dim query As String = "SELECT TOP 1 * FROM TBL_COMUNI WHERE COMUNE = ?"
            
            Using cmd As New OdbcCommand(query, cn)
                
                ' ODBC doesn't use named parameters, so only the order matters here:
                cmd.Parameters.AddWithValue("p0", txtPaese.Text)
                
                ' No need for the DataSet / OdbcDataAdapter code here,
                ' since you're not using the loaded data anyway.
                
                cn.Open()
                
                Using reader As OdbcDataReader = cmd.ExecuteReader(CommandBehiavor.CloseConnection)
                    If reader.Read() Then
                        ' TODO: Update the column index when you change the query,
                        '       or use the column name instead.
                        Me.txtCAP.Text = reader.Item(11)
                        Me.txtPR.Text = reader.Item(4)
                    Else
                        ' TODO: The record was not found. Tell the user.
                    End If
                End Using
            End Using
        End Using
        
    Catch ex As Exception
        MsgBox("Error: " & ex.Source & ": " & ex.Message, MsgBoxStyle.OkOnly, "Connection Error !!")
    End Try
End Sub

Aaron Rosenthal wrote:

This causes me to continue buffering in a loop until GetChars returns 0

Aaron Rosenthal wrote:

I think this is very inefficient and is slowing down my program

Bastard Programmer from Hell
If you can't read my code, try converting it here[^]

Aaron Rosenthal wrote:

Why does it do that?

Bastard Programmer from Hell
If you can't read my code, try converting it here[^]

retval = reader.GetChars(0, startIndex, outChar, 0, bufferSize)
Do Until retval = 0
    myxml.WriteRaw(outChar, 0, retval)
    myxml.Flush()
    
    startIndex += retval
    Array.Clear(outChar, 0, retval)
    retval = reader.GetChars(0, startIndex, outChar, 0, bufferSize)
Loop

rawStr = New String(outChar, 0, retval)

myxml.WriteRaw(outChar, 0, retval)

retval = reader.GetChars(0, startIndex, outChar, 0, bufferSize)
Do Until retval = 0
    Dim nullIndex = Array.IndexOf(outChar, Chr(0), 0, retval)
    If nullIndex = -1 Then nullIndex = retval
    
    myxml.WriteRaw(outChar, 0, nullIndex)
    myxml.Flush()
    
    startIndex += retval
    Array.Clear(outChar, 0, retval)
    retval = reader.GetChars(0, startIndex, outChar, 0, bufferSize)
Loop

System.Data.OracleClient Namespace | MSDN[^]:

The types in System.Data.OracleClient are deprecated and will be removed in a future version of the .NET Framework.

• Official Oracle ODP.NET, Managed Driver[^]
• Official Oracle ODP.NET, Managed Entity Framework Driver[^]

Using lob As OracleLob = reader.GetOracleLob(0)
    Using sr As New StreamReader(lob, Text.Encoding.Unicode) ' <-- You might need to adjust this
        retval = sr.Read(outChar, 0, bufferSize)
        Do Until retval = 0
            myxml.WriteRaw(outChar, 0, retval)
            myxml.Flush()
            
            Array.Clear(outChar, 0, retval)
            retval = sr.Read(outChar, 0, bufferSize)
        Loop
    End Using
End Using

1. The GetChars method creates a new OracleLob on each call, and reads its Value property.
2. The Value property reads the entire string into memory on each call.
3. The GetChars method then copies the string to a Char array.
4. The GetChars method then copies the specified section of the array to the buffer you've passed in.

Richard Deeming wrote:

EDIT: Looking at the code in dotPeek, this will be much more efficient
than calling GetChars:

Bastard Programmer from Hell
If you can't read my code, try converting it here[^]

// OracleDataReader.GetChars:
public override long GetChars(int i, long fieldOffset, char[] buffer2, int bufferoffset, int length)
{
    // Pre-condition checks omitted
    return this._columnInfo[i].GetChars(this._buffer, fieldOffset, buffer2, bufferoffset, length);
}

// OracleColumn.GetChars:
internal long GetChars(NativeBuffer_RowBuffer buffer, long fieldOffset, char[] destinationBuffer, int destinationOffset, int length)
{
    // Pre-condition checks omitted
    
    int result;
    if (this.IsLob)
    {
        // The OP said it's a CLOB column, so we're in this branch.
        using (OracleLob oracleLob = new OracleLob(this._lobLocator))
        {
            string str = (string) oracleLob.Value;
            int length1 = str.Length;
            int startIndex = (int)fieldOffset;
            result = length1 - startIndex;
            if (destinationBuffer != null)
            {
                result = Math.Min(result, length);
                if (0 < result) Buffer.BlockCopy(str.ToCharArray(startIndex, result), 0, destinationBuffer, destinationOffset, result);
            }
        }
    }
    else
    {
        // Omitted
    }
    
    return (long) Math.Max(0, result);
}

// OracleLob.Value:
public object Value
{
    get
    {
        // Pre-condition checks omitted
        
        long num = this._currentPosition;
        try
        {
            this.Seek(0L, SeekOrigin.Begin);
            if (this._lobType == OracleType.Blob || this._lobType == OracleType.BFile)
            {
                // Code to read and return a byte array omitted, since we're read a CLOB.
            }
            
            return new StreamReader(this, Encoding.Unicode).ReadToEnd();
        }
        finally
        {
            this._currentPosition = num;
        }
    }
}

1. The OracleLob.Value property reads the entire CLOB value into memory as a string;
2. The OracleColumn.GetChars method calls ToCharArray which copies (a portion of) the string to a new array;
3. It then uses Buffer.BlockCopy to copy the characters from the new array to the destinationBuffer array;