JPA之JPQL基础查询 曾经终败给现在 2022-05-21 07:44 273阅读 0赞 @NamedQuery(name="test_jpql",query="SELECT t FROM TestJPQL t") @Entity @Table(name="TEST_JPQL") public class TestJPQL { private Integer id; private String name; private String address; public TestJPQL(String name, String address) { super(); this.name = name; this.address = address; } public TestJPQL() { super(); } @Id @GeneratedValue public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getAddress() { return address; } public void setAddress(String address) { this.address = address; } @Override public String toString() { return "TestJPQL [id=" + id + ", name=" + name + ", address=" + address + "]"; } } **`createQuery查询基础`** Query createQuery = entityManager.createQuery("SELECT t FROM TestJPQL t"); @SuppressWarnings("unchecked") List<TestJPQL> resultList = createQuery.getResultList(); System.out.println(resultList); 代码中通过对象`TestJPQL`查询数据,调用`getResultList`返回一个List结果集 **`createQuery之new对象代码`** Query createQuery = entityManager.createQuery("SELECT new TestJPQL(t.name,t.address) FROM TestJPQL t"); @SuppressWarnings("unchecked") List<TestJPQL> resultList = createQuery.getResultList(); System.out.println(resultList); 通过在语句中`new`一个对象,将对应元素以对应参数传入查询。`注意: 此时需要对实体类添加对应的有参构造器和和无参构造器`。 **`createNamedQuery代码`** Query createQuery = entityManager.createNamedQuery("test_jpql"); @SuppressWarnings("unchecked") List<TestJPQL> resultList = createQuery.getResultList(); System.out.println(resultList); 在实体类需要添加`@NamedQuery`注解,`name`为`createNamedQuery`方法传入的参数,`query`为JPQL语句,可以有select部分,也没有没有。 **`createNativeQuery`** Query createQuery = entityManager.createNativeQuery("SELECT id FROM test_jpql WHERE id = ? "); createQuery.setParameter(1, 1); Object singleResult = createQuery.getSingleResult(); System.out.println(singleResult); 通过`createNativeQuery`方法,传入SQL查询。且只能返回一个元素\[即只能查询指定行的某列数据\], 所以通过`getSingleResult`查询出对应列的数据。
还没有评论,来说两句吧...