jpql三种query

最新推荐文章于 2025-05-22 18:39:29 发布

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本文通过一个Java示例展示了如何使用Java Persistence Query Language (JPQL) 和 Native Query 进行数据库查询。示例包括EntityManager的创建、事务管理、查询执行及结果获取等关键步骤。

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package jpaHello;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.EntityTransaction;
import javax.persistence.Persistence;
import javax.persistence.Query;

public class JPQL {
public static void main(String[] args) {


//persistence.xml文件中persistence-unit标签name属性值
String persistenceUnitName = "JPA";
//1.创建EntitymanagerFactory

Map<String, Object> properities=new HashMap<String, Object>();

properities.put("hibernate.show_sql", true);

EntityManagerFactory entityManagerFactory =
Persistence.createEntityManagerFactory(persistenceUnitName,properities );

//2.创建EntityManager
EntityManager entityManager = entityManagerFactory.createEntityManager();

//3.开启事务
EntityTransaction transaction = entityManager.getTransaction();
transaction.begin();

//4.进行持久化操作
//createQuery
/*String jpql="from Customer c where c.age = :age";
Query query=entityManager.createQuery(jpql);

query.setParameter("age", 20);
List<Customer> list=query.getResultList();
System.out.println(list.size());*/

//createNamedQuery

/*Query query=entityManager.createNamedQuery("testNamedQuery").setParameter("age", 10);
Customer customer=(Customer) query.getSingleResult();
System.out.println(customer);*/

//nativeQuery
String jpql="select name from Customers where age > ?";
Query query=entityManager.createNativeQuery(jpql)
.setParameter(1, 10);
Object result=query.getSingleResult();
System.out.println(result);

//5. 提交事务
transaction.commit();

//6.关闭EntityManager
entityManager.close();

//7.关闭EntityManager
entityManagerFactory.close();

}
}