使用JPQL语句进行数据库操作查询

JPQL：Java Persistence Query Language  即java持久化查询语言

jpql和sql查询之间的区别

sql ：sql语句中查询的是表和表中的字段

jpql：sql语句中查询的是实体类和实体类中对应的属性

首先建立一个工程，具体的工程我的博客里面有，大家可以去找一下

然后创建test测试类

package com.w.test;

import com.w.entity.Customer;
import com.w.util.JpaUtils;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import javax.persistence.EntityManager;
import javax.persistence.EntityTransaction;
import javax.persistence.Query;
import java.util.List;

public class TestJpql {
    EntityManager entityManager;
    EntityTransaction transaction;
    @Before
    public void before(){
        entityManager = JpaUtils.getEntityManager();
        transaction = entityManager.getTransaction();
        transaction.begin();

    }
    @After
    public void after(){
        transaction.commit();
        entityManager.close();
    }
    @Test
    public void testFindAll(){
        Query query = entityManager.createQuery("from com.w.entity.Customer ");
        List customers = query.getResultList();
        for (Customer customer : customers) {
            System.out.println(customer);
        }
    }
    @Test
    public void testOrder(){
        Query query = entityManager.createQuery("from com.w.entity.Customer ORDER BY cId desc");
        List customers = query.getResultList();
        for (Customer customer : customers) {
            System.out.println(customer);
        }
    }
    @Test
    public void testCount(){
        Query query = entityManager.createQuery("select count(cId)  from com.w.entity.Customer ORDER BY cId desc");
        Object result = query.getSingleResult();
        System.out.println(result);
    }
    @Test
    public void testLimit(){
        Query query = entityManager.createQuery("from com.w.entity.Customer ORDER BY cId desc");
        //显示多少条
        query.setMaxResults(2);
        //起始条数
        query.setFirstResult(0);
        List customers = query.getResultList();
        for (Customer customer : customers) {
            System.out.println(customer);
        }
    }
    @Test
    public void testCondition(){
        //问号后面的数字表示的是第几个占位符
        Query query = entityManager.createQuery("from com.w.entity.Customer where cName like ?1");
        query.setParameter(1,"%三%");
        //显示多少条
        query.setMaxResults(2);
        //起始条数
        query.setFirstResult(0);
        List customers = query.getResultList();
        for (Customer customer : customers) {
            System.out.println(customer);
        }
    }
}

jpaUtils

package com.w.util;

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

public class JpaUtils {
    static EntityManagerFactory factory;
    static {
         factory = Persistence.createEntityManagerFactory("jpa1");
    }
    public static EntityManager getEntityManager(){
        return factory.createEntityManager();
    }
}