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copied!<p><strong><code>@JoinColumn</code> could be used on both sides of the relationship.</strong> The question was about using <code>@JoinColumn</code> on the <code>@OneToMany</code> side (rare case). And the point here is in <em>physical information duplication</em> (column name) along with <em>not optimized SQL query that will produce some additional UPDATE statements</em>.</p> <p>According to <a href="http://docs.jboss.org/hibernate/annotations/3.5/reference/en/html_single/">documentation</a>:</p> <p>Since <strong>many to one are</strong> (almost) always the <strong>owner side</strong> of a bidirectional relationship in the JPA spec, the one to many association is annotated by @OneToMany(mappedBy=...)</p> <pre><code>@Entity public class Troop { @OneToMany(mappedBy="troop") public Set<Soldier> getSoldiers() { ... } @Entity public class Soldier { @ManyToOne @JoinColumn(name="troop_fk") public Troop getTroop() { ... } </code></pre> <p>Troop has a bidirectional one to many relationship with Soldier through the troop property. You don't have to (must not) define any physical mapping in the mappedBy side.</p> <p>To map a bidirectional one to many, with the <strong>one-to-many side as the owning side</strong>, you have to remove the mappedBy element and set the many to one @JoinColumn as insertable and updatable to false. This solution is not optimized and will produce some additional UPDATE statements.</p> <pre><code>@Entity public class Troop { @OneToMany @JoinColumn(name="troop_fk") //we need to duplicate the physical information public Set<Soldier> getSoldiers() { ... } @Entity public class Soldier { @ManyToOne @JoinColumn(name="troop_fk", insertable=false, updatable=false) public Troop getTroop() { ... } </code></pre>

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