5.9.1. Refresh gotchas

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The `refresh` entity state transition is meant to overwrite the entity attributes according to the info currently contained in the associated database record.

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However, you have to be very careful when cascading the refresh action to any transient entity.

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For instance, consider the following example:

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<div class="title">Example 246. Refreshing entity state gotcha</div>
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<pre class="prettyprint highlight">`try {
    Person person = entityManager.find( Person.class, personId );

    Book book = new Book();
    book.setId( 100L );
    book.setTitle( "Hibernate User Guide" );
    book.setAuthor( person );
    person.getBooks().add( book );

    entityManager.refresh( person );
}
catch ( EntityNotFoundException expected ) {
    log.info( "Beware when cascading the refresh associations to transient entities!" );
}`</pre>
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In the aforementioned example, an `EntityNotFoundException` is thrown because the `Book` entity is still in a transient state.
When the refresh action is cascaded from the `Person` entity, Hibernate will not be able to locate the `Book` entity in the database.

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For this reason, you should be very careful when mixing the refresh action with transient child entity objects.

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