JPA学习---第八节：使用JPQL语句进行查询

@Test
public void query(){
    EntityManagerFactory factory = Persistence.createEntityManagerFactory("learn_jpa");
    EntityManager em = factory.createEntityManager();
    // 命名参数查询或位参数查询
    Query query = em.createQuery("select p from Person p p.id = ?1");
    query.setParameter(1, 1);
    // 调用 getSingleResult() 方法，必须要有结果(也就是说数据库必须要有对应的数据)，不然会保存
    Person person = (Person)query.getSingleResult();
    System.out.println(person.getName());
    em.close();
    factory.close();
}

@Test
public void deletequery(){
    EntityManagerFactory factory = Persistence.createEntityManagerFactory("learn_jpa");
    EntityManager em = factory.createEntityManager();
    em.getTransaction().begin();
    // 命名参数查询或位参数查询
    Query query = em.createQuery("delete from Person p where p.id = ?1");
    query.setParameter(1, 1);
    query.executeUpdate();
    em.getTransaction().commit();
    em.close();
    factory.close();
}

@Test
public void updatequery(){
    EntityManagerFactory factory = Persistence.createEntityManagerFactory("learn_jpa");
    EntityManager em = factory.createEntityManager();
    em.getTransaction().begin();
    // 命名参数查询
    Query query = em.createQuery("update Person p set name=:name where p.id = :id");
    query.setParameter("name", "hwl");
    query.setParameter("id", 3);
    query.executeUpdate();
    em.getTransaction().commit();
    em.close();
    factory.close();
}

package learn.jpa.junit.test;

import static org.junit.Assert.*;

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

import learn.jpa.bean.Person;

import org.junit.Test;

public class PersonTest {

    @Test
    public void save(){
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("learn_jpa");
        EntityManager em = factory.createEntityManager();
        em.getTransaction().begin();   // 开启事务
        em.persist(new Person("hwl"));
        em.getTransaction().commit();
        em.close();
        factory.close();
    }

    /**
     * 查询
     */
    @Test
    public void getPerson(){
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("learn_jpa");
        EntityManager em = factory.createEntityManager();
        // 第一个参数表示 实体类   第二个参数表示 实体标识符
        Person person = em.find(Person.class, 1);
        System.out.println(person.getName());
        em.close();
        factory.close();
    }
    
    @Test
    public void getPerson2(){
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("learn_jpa");
        EntityManager em = factory.createEntityManager();
        // 第一个参数表示 实体类   第二个参数表示 实体标识符
        // 调用这个方法时，并不会立即从数据库中得到数据，只是返回一个代理对象
        Person person = em.getReference(Person.class, 1);
        // 当我们对代理对象的属性进行访问的时候，才会从数据库中获取数据
        // 如果执行以上方法，数据库中没有对应的数据，是不会报错的，会在执行 person.getName() 时才异常
        System.out.println(person.getName());
        em.close();
        factory.close();
    }
    
    @Test
    public void updatePerson(){
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("learn_jpa");
        EntityManager em = factory.createEntityManager();
        // 实体管理器已于事务关联
        em.getTransaction().begin();
        // 查找出来后 person 对象在 CPU 时处于托管状态
        // 这时调用实体类的 set 方法，可以对数据进行更改，但并不是立即更改，是放在 JDBC 的批处理交易库里面
        Person person = em.find(Person.class, 1);
        person.setName("zxx");
        // 调用事务提交后，会将数据同步到数据库中
        em.getTransaction().commit();
        em.close();
        factory.close();
        
        // 实体在 CPU 中有四种状态  
        //第一种 新建(new) 第二种 托管(manage)  第三种 游离  第四种 删除
    }
    
    @Test
    public void updatePerson2(){
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("learn_jpa");
        EntityManager em = factory.createEntityManager();
        em.getTransaction().begin();
        Person person = em.find(Person.class, 1);
        em.clear(); // 将实体管理器中的所有实体状态变成游离状态
        person.setName("zxx");
        em.merge(person); // 将游离状态的数据更新同步到数据库
        em.getTransaction().commit();
        em.close();
        factory.close();
    }
    
    @Test
    public void delete(){
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("learn_jpa");
        EntityManager em = factory.createEntityManager();
        em.getTransaction().begin();
        Person person = em.find(Person.class, 1);
        em.remove(person);
        em.getTransaction().commit();
        em.close();
        factory.close();
    }
    
    @Test
    public void query(){
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("learn_jpa");
        EntityManager em = factory.createEntityManager();
        // 命名参数查询或位参数查询
        Query query = em.createQuery("select p from Person p p.id = ?1");
        query.setParameter(1, 1);
        // 调用 getSingleResult() 方法，必须要有结果(也就是说数据库必须要有对应的数据)，不然会保存
        Person person = (Person)query.getSingleResult();
        System.out.println(person.getName());
        em.close();
        factory.close();
    }
    
    @Test
    public void deletequery(){
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("learn_jpa");
        EntityManager em = factory.createEntityManager();
        em.getTransaction().begin();
        // 命名参数查询或位参数查询
        Query query = em.createQuery("delete from Person p where p.id = ?1");
        query.setParameter(1, 1);
        query.executeUpdate();
        em.getTransaction().commit();
        em.close();
        factory.close();
    }
    
    @Test
    public void updatequery(){
        EntityManagerFactory factory = Persistence.createEntityManagerFactory("learn_jpa");
        EntityManager em = factory.createEntityManager();
        em.getTransaction().begin();
        // 命名参数查询
        Query query = em.createQuery("update Person p set name=:name where p.id = :id");
        query.setParameter("name", "hwl");
        query.setParameter("id", 3);
        query.executeUpdate();
        em.getTransaction().commit();
        em.close();
        factory.close();
    }
}