title: Get Unable to obtain an object lock on "null".; org.apache.openjpa.persistence.OptimisticLockException:
body: <p>This is a Spring application with Roo and the exception thrown by a simple finder function like:</p>
  
  <pre><code> TransactionRate.findAllTransactionRate(TransactionRate.java:1)
  </code></pre>
  
  <p>The exception only happens to <code>TransactionRate</code> entity but not the other 20 entities. I am pretty sure their is no other entityManager is reading/editing on the entity so that table should not be locked. The persistent.xml looks clear. </p>
  
  <p>I used to have similar issue but just remember the solution is to change something else in configuration(like persistence.xml), really cannnot recall details. </p>
  
  <p>Please share any ideas. Thank you.</p>