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POUnderstanding Hibernate transactions
 

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    <p>I understand that a transaction helps to rollback update operations if anything goes wrong such as a code exception or if the database is down. What I do not understand is the following:</p> <p>In <a href="http://docs.jboss.org/hibernate/orm/4.2/manual/en-US/html/ch13.html#transactions-demarcation" rel="nofollow">this page</a>:</p> <blockquote> <p>13.2. Database transaction demarcation</p> <p>Database, or system, transaction boundaries are always necessary. No communication with the database can occur outside of a database transaction (this seems to confuse many developers who are used to the auto-commit mode). Always use clear transaction boundaries, even for read-only operations</p> </blockquote> <p>This one says that a transaction should be used in all cases, even for <strong>read-only operations</strong> !</p> <ul> <li>Why is it a must ? Shouldn't I do so only when I'm about to update the database ?</li> <li>If it's a must, why isn't it started automatically when a session is obtained ?</li> </ul> <p>Regarding the following quoted paragraph (On <a href="http://docs.jboss.org/hibernate/orm/4.2/manual/en-US/html/ch02.html#architecture-overview" rel="nofollow">this page</a>).</p> <blockquote> <p>Transaction (org.hibernate.Transaction)</p> <p>(Optional) A single-threaded, short-lived object used by the application to specify atomic units of work. It abstracts the application from the underlying JDBC, JTA or CORBA transaction. A org.hibernate.Session might span several org.hibernate.Transactions in some cases. However, transaction demarcation, either using the underlying API or org.hibernate.Transaction, is never optional.</p> </blockquote> <p>What is meant by the first word <code>(Optional)</code> indicate ?</p> <p>And what does this statement mean too ?</p> <p><code>However, transaction demarcation, either using the underlying API or org.hibernate.Transaction, is never optional.</code> ?!</p> <p>Also I understand from <a href="http://docs.jboss.org/hibernate/orm/4.2/manual/en-US/html/ch01.html" rel="nofollow">this page</a>, that whenever I open a Hibernate session whether to update or load an object, I <strong>must</strong> start a transaction.</p>
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