jpa EntityManager的方法

一、EntityManager各种方法

1、persist

persist把实体类进行持久化，相当于增加操作

  User user = new User();

        user.setSex(false);
        user.setName("小白");
        user.setBirth(new Date());
        user.setAge(18);

        entityManager.persist(user);

2、find

find 会根据id把数据库的实体类查询出来

@Test
public void findTest(){
    User user = entityManager.find(User.class, 1);

    System.out.println(user);
}

3、Reference

reference 会根据id把数据库的实体类查询出来 但是用实体类的时候他才会查询出来

@Test
public void refrenceTest(){
    User user = entityManager.getReference(User.class, 1);

    System.out.println("---------------------");

    System.out.println(user);
}

4、remove

remove 会把根据查出来的数据删除对用字段

@Test
public void removeTest(){

    User user = entityManager.find(User.class, 1);

    entityManager.remove(user);

    System.out.println(user);
}

5、merge

是根据转入的实体类状态对数据库进行增加或者进行修改

Customer customer=new Customer();
customer.setLastName("fu");
customer.setEmail("[email protected]");
customer.setBirth(new Date());
customer.setCreatedTime(new Date());
customer.setAge(15);

Customer customer1 = entityManager.merge(customer);
System.out.println("customer01: "+customer.getId());

System.out.println("customer02: "+customer1.getId());

6、flush

会把查出来的数据跟数据库同步

Customer customer = entityManager.find(Customer.class, 1);

System.out.println(customer);

customer.setLastName("BB");

entityManager.flush();