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POOne-To-Many child has already been persisted without parent
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  1. POOne-To-Many child has already been persisted without parent
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    copied!<p>I'm using the Google App Engine in combination with the Google Web Toolkit to write a bug tracker (to see what the technologies are capable of).</p> <p>Modelled after Google Code's issue tracker, I decided that an issue can have 0 or more labels, that can be defined beforehand (let's say in the settings).</p> <p>The label class (CustomLabel):</p> <pre><code>@PersistenceCapable(identityType = IdentityType.APPLICATION) public class CustomLabel implements Serializable { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) @Extension(vendorName="datanucleus", key="gae.encoded-pk", value="true") private String encodedKey; @Persistent @Extension(vendorName="datanucleus", key="gae.pk-id", value="true") private Long keyId; /** * label caption. */ @Persistent private String caption; // Unimportant getters / setters } </code></pre> <p>Now the parent class (Issue):</p> <pre><code>@PersistenceCapable(identityType = IdentityType.APPLICATION) public class Issue implements Serializable { private static final long serialVersionUID = 1L; @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) private Long id; // Replacing the Long key by this key doesn't make a difference // @PrimaryKey // @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) // @Extension(vendorName="datanucleus", key="gae.encoded-pk", value="true") // private String encodedKey; @Persistent private String summary; @Persistent private String description; @Persistent private ArrayList&lt;CustomLabel&gt; labels; // Other details } </code></pre> <p>When I'm trying to persist a new Issue with existing CustomLabels I get the following exception:</p> <pre><code>org.datanucleus.exceptions.NucleusUserException: Detected attempt to establish Issue(11) as the parent of CustomLabel(1) but the entity identified by CustomLabel(1) has already been persisted without a parent. A parent cannot be established or changed once an object has been persisted. </code></pre> <p>How can this be solved? I cannot use Key's and create an unowned relationship, since I'm sending the objects to the GWT front-end (which is compiled to Javascript and com.google.appengine.api.datastore.Key isn't supported). Besides that would break referential integrity, which is undesirable. </p>
 

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