C# SQLiteCommand.ExecuteScalar方法代码示例

        /// <summary>
        /// Execute a SQLiteCommand (that returns a 1x1 resultset) against the specified SQLiteTransaction
        /// using the provided parameters.
        /// </summary>
        /// <remarks>
        /// e.g.:  
        ///  int orderCount = (int)ExecuteScalar(trans, CommandType.Text, "Select count(Order) from TableTransaction where ProdId=?", new SQLiteParameter("@prodid", 24));
        /// </remarks>
        /// <param name="transaction">A valid SQLiteTransaction</param>
        /// <param name="commandType">The CommandType (TableDirect, Text)</param>
        /// <param name="commandText">The T-SQL command</param>
        /// <param name="commandParameters">An array of SQLiteParamters used to execute the command</param>
        /// <returns>An object containing the value in the 1x1 resultset generated by the command</returns>
        public static object ExecuteScalar(SQLiteTransaction transaction, CommandType commandType, string commandText, params SQLiteParameter[] commandParameters)
        {
            if( transaction == null ) throw new ArgumentNullException( "transaction" );
            if( transaction != null && transaction.Connection == null ) throw new ArgumentException( "The transaction was rollbacked or commited, please provide an open transaction.", "transaction" );

            // Create a command and prepare it for execution
            SQLiteCommand cmd = new SQLiteCommand();
            bool mustCloseConnection = false;
            PrepareCommand(cmd, (SQLiteConnection)transaction.Connection, transaction, commandType, commandText, commandParameters, out mustCloseConnection);

            // Execute the command & return the results
            object retval = cmd.ExecuteScalar();

            // Detach the SQLiteParameters from the command object, so they can be used again
            cmd.Parameters.Clear();
            return retval;
        }

        // If it's an Insert we fetch the @@Identity value and stuff it in the proper column
        protected void OnRowUpdated(object sender, RowUpdatedEventArgs e)
        {
            try
            {
                if(e.Status == UpdateStatus.Continue && e.StatementType == StatementType.Insert)
                {
                    TransactionMgr txMgr = TransactionMgr.ThreadTransactionMgr();

                    string[] identityCols = this.GetAutoKeyColumns().Split(';');

                    SQLiteCommand cmd = new SQLiteCommand();

                    foreach(string col in identityCols)
                    {
                         cmd.CommandText = "SELECT last_insert_rowid()";

                        // We make sure we enlist in the ongoing transaction, otherwise, we
                        // would most likely deadlock
                        txMgr.Enlist(cmd, this);
                        object o = cmd.ExecuteScalar(); // Get the Identity Value
                        txMgr.DeEnlist(cmd, this);

                        if(o != null)
                        {
                            e.Row[col] = o;
                        }
                    }

                    e.Row.AcceptChanges();
                }
            }
            catch {}
        }