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copied!<p>When you are working with JPA, you should think Object and relations between Objects and you should map your Object model, not <code>ids</code>, to your relational model (it is possible to map a <code>List</code> of basic values with <a href="http://en.wikibooks.org/wiki/Java_Persistence/ElementCollection" rel="nofollow noreferrer"><code>@ElementCollection</code></a> in JPA 2.0 though but what I said just before still applies).</p> <p>Here, (assuming this really is a <strong>one-to-many</strong> relation between <code>Message</code> and <code>GroupAssoc</code> and not a <strong>many-to-many</strong> relation between <code>Message</code> and <code>Group</code> entities) you should have something like this:</p> <pre><code>@Entity @Table(name = "MESSAGE") public class Message implements Serializable { @Id @Column(name = "MESSAGE_ID") @GeneratedValue(strategy = GenerationType.IDENTITY) private Long messageId; @OneToMany(fetch=FetchType.LAZY, cascade=CascadeType.PERSIST) private List<GroupAssoc> groupAssocs = new ArrayList<GroupAssoc>(); public Long getMessageId() { return messageId; } public void setMessageId(Long messageId) { this.messageId = messageId; } public List<GroupAssoc> getGroupAssocs() { return groupAssocs; } public void setGroupAssocs(List<GroupAssoc> groupAssocs) { this.groupAssocs = groupAssocs; } // equals() and hashCode() } </code></pre> <p>And another entity for <code>GroupAssoc</code>.</p> <p>PS: Your DDL really looks like a (M:N) relation between <code>MESSAGE</code> and <code>GROUP</code> (or I don't understand the PK constraint of <code>GROUP_ASSOC</code>) but you didn't show any FK constraint on <code>GROUP_ID</code> so I'm not 100% sure. But if that's the case, then you should use an <code>@ManyToMany</code> instead of <code>@OneToMany</code>.</p>

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