JPA:Eclipselink不尊重em.remove()

Question

我需要删除一个实体并创建另一个实体:

@Stateless
public class StatelessBean {
  @PersistenceUnit(unitName = "Unit001")
  EntityManagerFactory emf;

  protected void test() {
    EntityManager em = emf.createEntityManager();
    MyObj obj1 = em.find(MyObj.class, 100);
    MyObj obj2 = new MyObj();
    obj2.setKey("the same unique key as in obj1");
    em.remove(obj1);
    // em.flush(); 
    em.persist(obj2); // works fine when flush() is uncommented
    em.close();
  }
}

如果我对 em.flush()保留评论，那么我会得到 com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException(新对象和旧对象的键值相等)

发生这种异常行为的原因可能是什么？

伺服器:Glassfish 3.1.2

Eclipse Persistence Services-2.3.2.v20111125-r10461

persistence.xml:

<persistence xmlns="http://java.sun.com/xml/ns/persistence" version="2.0">
  <persistence-unit name="Unit001">
    <jta-data-source>jdbc/Unit001DS</jta-data-source>
    <properties>
      <property name="eclipselink.logging.level" value="INFO"/>
      <property name="eclipselink.target-database" value="MySQL"/>
    </properties>
  </persistence-unit>
</persistence>

连接池:

${ASADMIN} --port ${DOMAIN_ADMIN_PORT}  create-jdbc-connection-pool --datasourceclassname com.mysql.jdbc.jdbc2.optional.MysqlConnectionPoolDataSource --restype javax.sql.ConnectionPoolDataSource --property "User=user:Password=pass:URL=jdbc\:mysql\://${DB_ADDRESS}/db" Unit001DS
${ASADMIN} --port ${DOMAIN_ADMIN_PORT}  create-jdbc-resource --connectionpoolid Unit001DS jdbc/Unit001DS

Answer 1

原因可能是Eclipselink如Eclipselink documentation所述在提交期间更改了操作顺序:

By default, EclipseLink does insert and update operations first, before delete operations, to ensure that referential integrity is maintained. This is the preferred approach.

您可以通过刷新(已经发现)或通过为Eclipselink设置特殊参数来更改此行为:

If you are forced to replace an object with unique constraints by deleting it and inserting a replacement, you may cause a constraint violation if the insert operation occurs before the delete operation. In this case, call setShouldPerformDeletesFirst to perform the delete operation before the insert operation.