title: Mapping to entity id with Hibernate
body: <p>Is there a way to map entities by their ID?</p>
  
  <p>Currently i have a code that works liek this:</p>
  
  <p>User object has some roles assigned to it:</p>
  
  <pre><code>@ManyToMany(fetch = FetchType.LAZY, cascade = {CascadeType.MERGE})
  @JoinTable(name = "USER_ROLES", joinColumns = {
          @JoinColumn(name = "USER_ID", nullable = false, updatable = false) },
          inverseJoinColumns = { @JoinColumn(name = "ROLE_ID", nullable = false, updatable = false) })
  protected List&lt;Role&gt; assignedRoles = new ArrayList&lt;&gt;();
  </code></pre>
  
  <p>Role is mapped to users:</p>
  
  <pre><code>@ManyToMany(fetch = FetchType.LAZY, mappedBy = "assignedRoles")
  protected Collection&lt;? extends User&gt; users;
  </code></pre>
  
  <p>The thing is, what i want is something like:</p>
  
  <pre><code>@ManyToMany(fetch = FetchType.LAZY, mappedBy = "assignedRoles")
  protected Collection&lt;Integer&gt; users;
  </code></pre>
  
  <p>To operate userIds instead of User objects.</p>
  
  <p>Is it possible to somehow configure Mapping to work this way? I failed to find anything on this in available Hibernate documentation.</p>