jpa – 必须在ConnectionDriverName属性“如何解决它？”中指定J

First : My data source name is EJB3BANK & my target database is SHOP .

第二：这是persistence.xml文件

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="1.0"
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_1_0.xsd">
<persistence-unit name="ShopJPA" transaction-type="JTA">
    <jta-data-source>jdbc/EJB3BANK</jta-data-source>
    <non-jta-data-source>jdbc/EJB3BANK</non-jta-data-source>
    <properties>
        <property name="openjpa.jdbc.Schema" value="SHOP" />
    </properties>
</persistence-unit>
</persistence>

第三：Item实体Class的部分代码

@Entity
@Table(schema = "SHOP",name = "ITEM")
@NamedQuery(name = "getItem",query = "SELECT i FROM Item i")
public class Item{...}

第四：这里是业务类CartBean,这里是问题的开始

@Stateful
CartBean implements Cart{
....
....
public List<Item> getItems() {      
javax.persistence.Query query = em.createNamedQuery("getItem");//the problem here
return query.getResultList();
}
}

这是错误消息：必须在ConnectionDriverName属性中指定JDBC驱动程序或DataSource类名.
如何解决这个问题？