Nontransactional data access Session session (Web design tools) = getSessionFactory().openSession(); Transaction
Nontransactional data access Session session = getSessionFactory().openSession(); Transaction tx = session.beginTransaction(); User u = (User) session.get(User.class, 123); session.lock(u, LockMode.FORCE); u.getDefaultBillingDetails().setOwner(”John Doe”); tx.commit(); session.close(); Any concurrent unit of work that works with the same User row now knows that this data was modified, even if only one of the values that you d consider part of the whole aggregate was modified. This technique is useful in many situations where you modify an object and want the version of a root object of an aggregate to be incremented. Another example is a modification of a bid amount for an auction item (if these amounts aren t immutable): With an explicit version increment, you can indicate that the item has been modified, even if none of its value-typed properties or collections have changed. The equivalent call with Java Persistence is em.lock(o, LockModeType.WRITE). You now have all the pieces to write more sophisticated units of work and create conversations. We need to mention one final aspect of transactions, however, because it becomes essential in more complex conversations with JPA. You must understand how autocommit works and what nontransactional data access means in practice. 10.3 Nontransactional data access Many DBMSs enable the so called autocommit mode on every new database connection by default. The autocommit mode is useful for ad hoc execution of SQL. Imagine that you connect to your database with an SQL console and that you run a few queries, and maybe even update and delete rows. This interactive data access is ad hoc; most of the time you don t have a plan or a sequence of statements that you consider a unit of work. The default autocommit mode on the database connection is perfect for this kind of data access after all, you don t want to type begin a transaction and end a transaction for every SQL statement you write and execute. In autocommit mode, a (short) database transaction begins and ends for each SQL statement you send to the database. You re working effectively nontransactionally, because there are no atomicity or isolation guarantees for your session with the SQL console. (The only guarantee is that a single SQL statement is atomic.)
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