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    <p>First, let's remind the various states of an entity. From the JPA 1.0 specification (in section 3.2 Entity Instance’s Life Cycle):</p> <blockquote> <p>This section describes the EntityManager operations for managing an entity instance’s lifecycle. An entity instance may be characterized as being new, managed, detached, or removed.</p> <ul> <li>A <strong>new</strong> entity instance has <strong>no persistent identity</strong>, and is not yet associated with a persistence context.</li> <li>A <strong>managed</strong> entity instance is an instance <strong>with a persistent identity</strong> that is currently associated with a persistence context.</li> <li>A <strong>detached</strong> entity instance is an instance <strong>with a persistent identity</strong> that is not (or no longer) associated with a persistence context.</li> <li>A <strong>removed</strong> entity instance is an instance with a persistent identity, associated with a persistence context, that is scheduled for removal from the database.</li> </ul> </blockquote> <p>And a graphical illustration:</p> <p><img src="https://openjpa.apache.org/builds/1.0.2/apache-openjpa-1.0.2/docs/manual/img/jpa-state-transitions.png" alt="alt text"></p> <p>So, by definition, a detached entity has already been persisted, and I actually don't think that this is your real question. Now, if you want to know if an entity is <em>new</em> (i.e. doesn't have any persistent identity), what about this:</p> <pre><code>@Transient public boolean isNew() { return (this.id == null); } </code></pre>
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    1. POHow to know if a detached JPA entity has already been persisted or not?
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    1. USPascal Thivent
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    1. POHow to know if a detached JPA entity has already been persisted or not?
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    1. COAbsolutely, I want to know if my entity is new. I would prefer use another field with a default value set in the database since I'm not using a JPA GeneratedValue strategy for the primary key (I'm setting myself the primary key with an UUID for cross database vendor/jpa implementation/clustering compatibility).
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    2. CO@snowflake The problem is that JPA doesn't support database generated values for non pk attributes so you'll have to use a JPA provider extension (like `@org.hibernate.annotations.Generated`) or to refresh your entities after persist, which is ugly. I wonder if using `@GeneratedValue` wouldn't be a better choice.
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      1. USPascal Thivent
    3. COThank you for your comment. You're right this is ugly, I would prefer using as an alternative a field set in and by my DAO.
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