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copied!<ul> <li><p>See the <a href="http://forum.hibernate.org/viewtopic.php?t=951275&highlight=difference+persist+save" rel="noreferrer">Hibernate Forum</a> for a explanation of the subtle differences between persist and save. It looks like the difference is the time the INSERT statement is ultimately executed. Since <strong>save</strong> does return the identifier, the INSERT statement has to be executed instantly regardless of the state of the transaction (which generally is a bad thing). <strong>Persist</strong> won't execute any statements outside of the currently running transaction just to assign the identifier. Save/Persist both work on <em>transient instances</em>, ie instances which have no identifier assigned yet and as such are not saved in the DB.</p></li> <li><p><strong>Update</strong> and <strong>Merge</strong> both work on <em>detached instances</em>, ie instances which have a corresponding entry in the DB but which are currently not attached to (or managed by) a Session. The difference between them are what happens to the instance which is passed to the function. <strong>update</strong> tries to reattach the instance, that means that there may be no other instance of the persistent entity attached to the Session right now otherwise a exception is thrown. <strong>merge</strong>, however, just copies all values to a persistent instance in the Session (which will be loaded if it is not currently loaded). The input object is not changed. So <strong>merge</strong> is more general than <strong>update</strong>, but may use more resources.</p></li> </ul>

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