Platform SDK: Transaction Server

Application Design Notes: Using Context and Transactions

[This product will work only on Windows NT 4.0 versions and earlier. For Windows 2000 and later, see COM+ (Component Services).]

Context simplifies defining transactions. A transaction is automatically started when a component is declared as transactional. Components don't need to add additional code to indicate the start and end of a transaction. Using context allows you to define the scope of a transaction.

Besides simplifying building components, automatic transaction enlistment also allows for reuse of existing components. Changing the transaction attribute is the only change to the Account component from the previous section, Building Scalable Components.

Creating the Account object from MoveMoney establishes MoveMoney as the root of the transaction. The root transaction attempts to commit after it has completed its work. If an Account object calls SetAbort to indicate that it cannot successfully commit its work, then when the root transaction attempts to commit, the entire transaction will fail.

In the case of a money transfer, this provides atomicity. If a credit succeeds, but insufficient funds prevent the debit from succeeding, then the credit will be rolled back from the database automatically. Thus, SetAbort provides simplified error recovery.

Context simplifies the development of the component. Each object independently acquires its own resources, performs its work, and indicates its own internal state by using SetComplete or SetAbort before returning.