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However, if we apply appropriate formatting based on the data, we will get different values, as follows: scott@ORA10G> select owa_opt_lock.checksum( to_char(12, '0009') || to_char(34, '0009')) from dual; 58853 scott@ORA10G> select owa_opt_lock.checksum( to_char(123, '0009') || to_char(4, '0009')) from dual; 58598 Thus, if we have a date column, date_col, we may have to format it with the format string to_char(date_col, 'yyyymmddhh24miss'), for example. The guiding philosophy in formatting the individual columns is that their concatenated value should be unique for any two different combinations of their individual values. Let s look at the class DemoOptLockingUsingChecksum, which invokes the preceding package opt_lock_chksum_demo and demonstrates optimistic locking. I will explain the class with interspersed comments as usual. The class begins with import statements and gets the connection as scott in the main() method: /* This program demonstrates optimistic locking using checksum * COMPATIBLITY NOTE: tested against 10.1.0.2.0.*/ import java.sql.SQLException; import java.sql.Connection; import java.sql.CallableStatement; import oracle.jdbc.OracleTypes; import book.util.JDBCUtil; import book.util.InputUtil; class DemoOptLockingUsingChecksum { public static void main(String args[]) throws Exception { Connection conn = null; try { conn = JDBCUtil.getConnection( "scott", "tiger", "ora10g" ); At this point, we again set the variable empNo to Martin s employee number. We invoke the _displayEmpDetails() method to display Martin s details on the imagined UI screen that allows the user to modify the details (the ename and sal column values in our example). The method will return the checksum of the row as well: int empNo = 7654; long rowChecksum = _displayEmpDetails( conn, empNo ); We then pause in using our InputUtil.waitTillUserHitsEnter() method, as we did in our earlier examples to simulate a user s think time: InputUtil.waitTillUserHitsEnter("Row has been selected but is not locked.");

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Caution F# lists and arrays are finite data structures built immediately rather than on demand, so you

At the end of the main() method, we invoke the _updateEmpInfo() method with the employee number, the new salary value, the new name, and the checksum we calculated earlier. This method simply invokes opt_lock_chksum_demo.update_emp_info. We close the connection in the finally clause as usual: _updateEmpInfo( conn, empNo, 1450, "MARTIN", rowChecksum ); } finally { JDBCUtil.close ( conn ); } }// end of main The following definitions of the methods _displayEmpDetails() and _updateEmpInfo() should be self-explanatory. These methods simply invoke the opt_lock_chksum_demo.get_ emp_details and opt_lock_chksum_demo.update_emp_info methods, respectively: private static long _displayEmpDetails( Connection conn, int empNo ) throws SQLException { CallableStatement cstmt = null; long rowChecksum = 0; int salary = 0; String empName = null; try { cstmt = conn.prepareCall( "{call opt_lock_chksum_demo.get_emp_details( , , , )}" ); cstmt.setInt( 1, empNo ); cstmt.registerOutParameter( 2, OracleTypes.VARCHAR ); cstmt.registerOutParameter( 3, OracleTypes.NUMBER ); cstmt.registerOutParameter( 4, OracleTypes.NUMBER ); cstmt.execute(); empName = cstmt.getString( 2 ); salary = cstmt.getInt( 3 ); rowChecksum = cstmt.getLong( 4 ); System.out.println( "empno: " + empNo + ", name: " + empName + ", salary: " + salary + ", checksum: " + rowChecksum ); } finally { JDBCUtil.close( cstmt ); } return rowChecksum; } private static void _updateEmpInfo( Connection conn, int empNo, int newSalary, String newEmpName, long rowChecksum ) throws SQLException

This chapter provides a brief introduction of Windows Communication Foundation, Microsoft s next-generation messaging stack that sets out to unify (or at least unite) MSMQ, COM+, Remoting, and Web Services.

{ CallableStatement cstmt = null; try { cstmt = conn.prepareCall( "{call opt_lock_chksum_demo.update_emp_info( , , , , )}" ); cstmt.setInt( 1, empNo ); cstmt.setInt( 2, newSalary ); cstmt.setString( 3, newEmpName ); cstmt.setLong( 4, rowChecksum ); cstmt.registerOutParameter( 5, OracleTypes.NUMBER ); cstmt.execute(); int numOfRowsUpdated = cstmt.getInt( 5 ); if( numOfRowsUpdated <= 0 ) { System.out.println( "Sorry. Someone else changed the data that you were trying to update. Please retry." ); } else { System.out.println( "You have successfully updated the employee information." ); } } finally { JDBCUtil.close( cstmt ); } } }// end of program Notice how we again use the number of rows updated to detect whether or not our update was successful. To test the program, we can run it exactly like we ran the program DemoOptLockingBySavingOldValues in two windows in the earlier section titled Optimistic Locking by Saving Old Column Values.

must take care that the length of the sequence is suitable. For example, [ 1I .. 1000000000I ] will attempt to build a list that is one billion elements long.

Optimistic Locking by Using the ora_rowscn Pseudo Column (10g Only)

F# is a typed language, and it is often necessary for the programmer to declare new shapes of types via type definitions and type abbreviations. In this chapter, we cover only some of the simpler type definitions that are useful and succinct workhorses for functional programming. F# also lets you define a range of sophisticated type definitions related to object-oriented programming, which we discuss in 6. However, these are often not required in basic functional programming.