title: apache derby + jpa
body: <p>I have embedded derby database and i work with jpa. This is my persistence.xml:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;persistence 
      version="2.0" 
      xmlns="http://java.sun.com/xml/ns/persistence" 
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
      xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"&gt;
      &lt;persistence-unit name="pers"&gt;
  
          &lt;class&gt;entities.Leverancier&lt;/class&gt;
          &lt;class&gt;entities.Prijsproduct&lt;/class&gt;
          &lt;class&gt;entities.Product&lt;/class&gt;
  
  
      &lt;/persistence-unit&gt;
  &lt;/persistence&gt;
  </code></pre>
  
  <p>What should i change or add to get this working. When I run my code now I get the following:</p>
  
  <pre><code>Exception in thread "main" javax.persistence.PersistenceException: No Persistence provider for EntityManager named pers
  at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:55)
  at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:33)
  at test.Test.main(Test.java:19)
  </code></pre>