Question

I have a trouble with the following code. The program seems to stuck sometimes (apparently no pattern…often in the second query since the form containing this code run but not always) for 5-20 seconds in the row

Dim rdr As SQLiteDataReader = cmd.ExecuteReader

If the code doesn’t stuck in second query since form started, it won’t never stuck. If I close and reopen the form I have the same 50-60% chance to have same error mostly on 2nd query.

Then it always restart from this point sometimes with no error…just big delay of 5-20 seconds and sometimes with error “The database file is locked, database is locked” at line

cmd.ExecuteNonQuery()
(2° time..not inside if block)

This error will forbid the user to save its change and sometimes corrupt the data record and, of course, introduces a huge delay that I can’t accept 🙁

Any Idea of what I’m doing wrong?

I’m developing with visual studio 2008 for a windows CE 6.0 device with 3.5 framework and

ADO.NET 2.0/3.5 SQLite Data Provider
Version 1.0.66.0 April 18, 2010
Using SQLite 3.6.23.1
http://sqlite.phxsoftware.com/

Thank you

'Update current program on database
Public Sub AggiornaUserOnDatabase(ByVal name As String, ByVal password As String, ByVal permission As String)
    'No spaces
    name = Trim(name)
    'Database var
    Dim ConString As String = "Data Source = " + DatabaseAccountPath + ";"
    Dim con As New SQLiteConnection
    Dim cmd As SQLiteCommand
    'Read from database
    Try
        con.ConnectionString = ConString
        con.Open()
        'Check if row is existing
        cmd = con.CreateCommand
        cmd.CommandText = "SELECT " + DBACCNAME + " FROM " + DatabaseAccountTableName + " WHERE " + DBACCNAME + " = '" + name + "'"
        Dim rdr As SQLiteDataReader = cmd.ExecuteReader
        'If empty...create the record
        If Not rdr.Read Then
            cmd = con.CreateCommand
            cmd.CommandText = "INSERT INTO " + DatabaseAccountTableName + " (" + DBACCNAME + ") VALUES ('" + name + "')"
            cmd.ExecuteNonQuery()
        End If
        rdr.close()
        'Update the values
        cmd = con.CreateCommand
        cmd.CommandText = "UPDATE " + DatabaseAccountTableName + " SET " _
                        + DBACCPASSWORD + " = '" + password + "', " _
                        + DBACCPERMISSION + " = '" + permission + "' " _
                        + "WHERE " + DBACCNAME + " = '" + name + "'"
        cmd.ExecuteNonQuery()
        cmd.Dispose()
        con.Close()
    Catch ex As Exception
        AggiungiRigaSuFile(ErroriPath, "Editing users account database: " + ex.Message, Configurazione.DiagnosticaOff, True)
    End Try
End Sub

Answer 1

You are using the cmd when it has an open reader. You need to close the reader before you use the cmd again. And don’t even use a reader. Do a select count(*) to to see if the record exists.

cmd.CommandText = "SELECT count(*) FROM " + ...
int rowRet = (Int32)sqlCmd2.ExecuteScalar();

if (rowCount == 0)
{
    // do NOT create the command gain just use it
    cmd.CommandText = "INSERT INTO " + DatabaseAccountTableName ...
    // insert all the values here so the update is not required
    cmd.ExecuteNonQuery();
}
else if (rowCount == 1)
{
    cmd.CommandText = "UPDATE " + DatabaseAccountTableName + " SET " _
                    + DBACCPASSWORD + " = '" + password + "', " _
                    + DBACCPERMISSION + " = '" + permission + "' " _
                    + "WHERE " + DBACCNAME + " = '" + name + "'"
    cmd.ExecuteNonQuery();
}
else 
{
     // throw an error expected 0 or 1
}