5.10.1. Reattaching detached data

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Reattachment is the process of taking an incoming entity instance that is in detached state and re-associating it with the current persistence context.

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JPA does not provide for this model. This is only available through Hibernate `org.hibernate.Session`.

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<div class="title">Example 247. Reattaching a detached entity using `lock`</div>
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<pre class="prettyprint highlight">`Person person = session.byId( Person.class ).load( personId );
//Clear the Session so the person entity becomes detached
session.clear();
person.setName( "Mr. John Doe" );

session.lock( person, LockMode.NONE );`</pre>
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<div class="title">Example 248. Reattaching a detached entity using `saveOrUpdate`</div>
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<pre class="prettyprint highlight">`Person person = session.byId( Person.class ).load( personId );
//Clear the Session so the person entity becomes detached
session.clear();
person.setName( "Mr. John Doe" );

session.saveOrUpdate( person );`</pre>
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The method name `update` is a bit misleading here.
It does not mean that an `SQL` `UPDATE` is immediately performed.
It does, however, mean that an `SQL` `UPDATE` will be performed when the persistence context is flushed since Hibernate does not know its previous state against which to compare for changes.
If the entity is mapped with `select-before-update`, Hibernate will pull the current state from the database and see if an update is needed.

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Provided the entity is detached, `update` and `saveOrUpdate` operate exactly the same.

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