我正在尝试使用以下简单代码来了解@Formula注释的工作原理。
我可以打印出描述和出价金额列的值，但用@Formula注释的字段，即shortDescription和averageBidAmount返回null。
请问有谁能指出代码的问题在哪里吗？
我在Mac OSX上使用Hibernate 5.0，postgresql-9.3-1102-jdbc41和TestNG。
import java.math.BigDecimal;
import java.util.List;
import javax.persistence.Entity;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Persistence;
import javax.transaction.UserTransaction;
import org.testng.annotations.Test;
import com.my.hibernate.env.TransactionManagerTest;
public class DerivedPropertyDemo extends TransactionManagerTest {
@Test
public void storeLoadMessage() throws Exception {
EntityManagerFactory emf = Persistence.createEntityManagerFactory("HelloWorldPU");
try {
{
UserTransaction tx = TM.getUserTransaction();
tx.begin();
EntityManager em = emf.createEntityManager();
DerivedProperty derivedProperty1 = new DerivedProperty();
derivedProperty1.description = "Description is freaking good!!!";
derivedProperty1.bidAmount = BigDecimal.valueOf(100D);
DerivedProperty derivedProperty2 = new DerivedProperty();
derivedProperty2.description = "Description is freaking bad!!!";
derivedProperty2.bidAmount = BigDecimal.valueOf(200D);
DerivedProperty derivedProperty3 = new DerivedProperty();
derivedProperty3.description = "Description is freaking neutral!!!";
derivedProperty3.bidAmount = BigDecimal.valueOf(300D);
em.persist(derivedProperty1);
em.persist(derivedProperty2);
em.persist(derivedProperty3);
tx.commit();
for (DerivedProperty dp : getDerivedProperty(em)) {
System.out.println("============================");
System.out.println(dp.description);
System.out.println(dp.bidAmount);
System.out.println(dp.getShortDescription());
System.out.println(dp.getAverageBidAmount());
System.out.println("#############################");
}
em.close();
}
} finally {
TM.rollback();
emf.close();
}
}
public List<DerivedProperty> getDerivedProperty(EntityManager em) {
List<DerivedProperty> resultList = em.createQuery("from " + DerivedProperty.class.getSimpleName()).getResultList();
return resultList;
}
}
我的实体类是：
@Entity
class DerivedProperty {
@Id
@GeneratedValue
protected Long id;
protected String description;
protected BigDecimal bidAmount;
@org.hibernate.annotations.Formula("substr(description, 1, 12)")
protected String shortDescription;
@org.hibernate.annotations.Formula("(select avg(b.bidAmount) from DerivedProperty b where b.bidAmount = 200)")
protected BigDecimal averageBidAmount;
public String getShortDescription() {
return shortDescription;
}
public BigDecimal getAverageBidAmount() {
return averageBidAmount;
}
}
编辑
我正在跟随《Java Persistence with Hibernate 2nd Ed.》这本书。
谢谢。