JPA-jpql查询语句的书写

（1）实体类

@NamedQueries({
        @NamedQuery(name = "getUserByAccount",query ="from User where account=?0"),
        @NamedQuery(name = "getUsers",query ="from User")
})
@Entity
@Table(name = "erp_user")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;
    private String account;
    private String password;
    @ManyToOne(cascade = CascadeType.PERSIST)
    @JoinColumn(name = "roleid")
    private Role role;
    //省略get和set方法
}

（2）测试类

public class QueryTest {
    private static EntityManagerFactory emf;
    private EntityManager em;
    private EntityTransaction tx;

    @BeforeClass
    public static void init() {
        emf = Persistence.createEntityManagerFactory("jpa");
    }

    @AfterClass
    public static void destory() {
        emf = null;
    }

    @Before
    public void setUp() {
        em = emf.createEntityManager();
        tx = em.getTransaction();
        tx.begin();
    }

    @After
    public void tearDown() {
        tx.commit();
        em.close();
    }

    @Test
    public void test1() {
        String jpql = "from User";
        TypedQuery<User> query = em.createQuery(jpql, User.class);
        List<User> users = query.getResultList();
        for (User user : users) {
            System.out.println(user.getAccount());
        }
    }

    @Test
    public void test2() {
        String jpql = "select u from User u";
        TypedQuery<User> query = em.createQuery(jpql, User.class);
        List<User> users = query.getResultList();
        for (User user : users) {
            System.out.println(user.getAccount());
        }
    }

    @Test
    public void test3() {
        String jpql = "select account from User";
        TypedQuery<String> query = em.createQuery(jpql, String.class);
        List<String> accounts = query.getResultList();
        for (String account : accounts) {
            System.out.println(account);
        }
    }

    @Test
    public void test4() {
        String jpql = "select account,password from User";
        TypedQuery<Object[]> query = em.createQuery(jpql, Object[].class);
        List<Object[]> objects = query.getResultList();
        for (Object[] object : objects) {
            System.out.println(object[0] + "--" + object[1]);
        }
    }

    @Test
    public void test5() {
        String jpql = "select u from User u where u.account = 'admin'";
        TypedQuery<User> query = em.createQuery(jpql, User.class);
        List<User> users = query.getResultList();
        for (User user : users) {
            System.out.println(user.getAccount());
        }
    }

    @Test
    public void test6() {
        String jpql = "select u from User u where u.account = ?0";
        TypedQuery<User> query = em.createQuery(jpql, User.class);
        query.setParameter(0, "admin");
        List<User> users = query.getResultList();
        for (User user : users) {
            System.out.println(user.getAccount());
        }
    }

    @Test
    public void test7() {
        String jpql = "select u from User u where u.account = :account";
        TypedQuery<User> query = em.createQuery(jpql, User.class);
        query.setParameter("account", "admin");
        List<User> users = query.getResultList();
        for (User user : users) {
            System.out.println(user.getAccount());
        }
    }

    @Test
    public void test8() {
        String jpql = "from User";
        TypedQuery<User> query = em.createQuery(jpql, User.class);
        query.setFirstResult(0);
        query.setMaxResults(3);
        List<User> users = query.getResultList();
        for (User user : users) {
            System.out.println(user.getAccount());
        }
    }

    @Test
    public void test9() {
        String jpql = "select count(*) from User";
        TypedQuery<Long> query = em.createQuery(jpql, Long.class);
        Long num = query.getSingleResult();
        System.out.println(num);
    }
    @Test
    public void test10() {
        TypedQuery<User> query = em.createNamedQuery("getUserByAccount",User.class);
        query.setParameter(0,"admin");
        User user = query.getSingleResult();
        System.out.println(user.getAccount());
    }
    @Test
    public void test11() {
        TypedQuery<User> query = em.createNamedQuery("getUsers", User.class);
        List<User> users = query.getResultList();
        for (User user : users) {
            System.out.println(user.getAccount());
        }
    }

}