title: SQL JPA - Multiple columns as primary key
body: <p>If i want severeal Column to make up an ID.</p>
  
  <p>SQL example :</p>
  
  <pre><code>CONSTRAINT [PK_NAME] PRIMARY KEY ([Column1],[Column2],[Column3])
  </code></pre>
  
  <p>How can i do that with a Jpa Entity class ? through columndefinition ?</p>
  
  <p>just setting the id field as:</p>
  
  <pre><code>value = Column1 + Column2 + Column3 // aint working.
  </code></pre>