2.10 Transaction Processing

There are two ways to control transactions through the DB2 CLI library:

setting isolation levels
using transaction control methods

Each of these techniques is described below.

2.10.1 Setting Isolation Levels

You can use the isolation() method of RWDBConnection to set the isolation level of the connected server. Table 4 shows the mapping between the IsolationType argument you pass, and the isolation level set by the SQLSetConnectionOption() call.

Table 4 -- Setting the isolation level

RWDBConnection:: IsolationType	ODBC Isolation Level	IBM Isolation Level
Unknown	`SQL_TXN_READ_UNCOMMITTED`	Uncommitted Read
ANSILevel1	`SQL_TXN_READ_COMMITTED`	Cursor Stability
ANSILevel2	`SQL_TXN_REPEATABLE_READ`	Read Stability
ANSILevel3	`SQL_TXN_SERIALIZABLE`	Repeatable Read

To determine the current isolation level, call RWDBConnection::isolation() without an argument.

2.10.2 Using Transaction Control Methods

You can explicitly control transactions through the following DBTools.h++ methods:

RWDBConnection::beginTransaction()
RWDBConnection::rollbackTransaction()
RWDBConnection::commitTransaction()

These methods have straightforward implementations that correspond to the following DB2 functions:

SQLSetConnectAttr(HDBC, SQL_ATTR_AUTOCOMMIT, SQL_AUTOCOMMIT_OFF)
SQLTransact(SQL_ROLLBACK)
SQLTransact(SQL_COMMIT)

An application can add the DBTools.h++ transaction methods to its code to take explicit control of its transaction blocks. The following code demonstrates how these methods can be used to commit or to rollback transactions:

// Assume we have a table myTable(c int) with no rows in it.
RWDBInserter ins= myTable.inserter();

cn1.beginTransaction ();         // Begin transaction..

(ins << 1 ).execute(cn1);        // First insertion
...
cn1.commitTransaction();         // Save first insertion

cn1beginTransaction();           // Begin another transaction
(ins << 2 ).execute(cn1);        // Second insertion
(ins << 3 ).execute(cn1);        // Third insertion
cn1.rollbackTransaction();       // Rollback transaction erasing
                                 // second and third insertions..

// The above program results in myTable holding one row of data.
// Its value is 1.

Please note that nested transactions and savepoint features are not supported by DB2.

NOTE: DB2 does not support nested transactions and savepoint features.

Attempting to create a nested transaction generates a server error. Attempting to use the savepoint features of the DBTools.h++ API generates the error RWDBStatus::notSupported for the connection that tried.