Spring Boot Jpa 默认提供 CURD 的方法等方法，在日常中往往时无法满足我们业务的要求，本章节通过自定义简单查询案例进行讲解。
快速上手
项目中的pom.xml、application.properties与 Chapter1 相同
实体类映射数据库表
user 实体类
@Entity
public class User implements Serializable {
private static final long serialVersionUID = -390763540622907853L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
private Integer age;
private String email;
// 省略构造器 set/get
}
自定义简单查询
spring data 内部基础架构中有个根据方法名的查询生成器机制，对于在存储库的实体上构建约束查询很有用。该机制方法的前缀有find…By、read…By、query…By、count…By和get…By，从这些方法可以分析它的其余部分（实体里面的字段）。引入子句可以包含其他表达式，例如在Distinct要创建的查询上设置不同的标志。然而，第一个By作为分隔符来指示实际标准的开始。在一个非常基本的水平上，你可以定义实体性条件，并与它们串联（And和Or）。
注：此段来自 《Spring Data JPA 从入门到精通》。
继承 PagingAndSortingRepository
public interface UserPagingRepository extends PagingAndSortingRepository<User, Long> {
// 通过姓名查找
List<User> findByName(String name);
// 通过姓名查找
List<User> queryByName(String name);
// 通过姓名或者邮箱查找
List<User> findByNameOrEmail(String name,String email);
// 计算某一个 age 的数量
int countByAge(int age);
}
测试类
路径：src/test/java/com/mtcarpenter/chapter2/repository/UserPagingRepositoryTest.java
@RunWith(SpringRunner.class)
@SpringBootTest
public class UserPagingRepositoryTest {
/**
* ⽇志对象
*/
private Logger logger = LoggerFactory.getLogger(UserPagingRepositoryTest.class);
@Autowired
private UserPagingRepository userPagingRepository;
@Before
public void save() {
logger.info("新增数据 result = {}", userPagingRepository.save(new User("小米", 9,"a@qq.com")));
logger.info("新增数据 result = {}", userPagingRepository.save(new User("张三", 16,"b@qq.com")));
logger.info("新增数据 result = {}", userPagingRepository.save(new User("三哥", 12,"c@qq.com")));
logger.info("新增数据 result = {}", userPagingRepository.save(new User("米二", 13,"e@qq.com")));
logger.info("新增数据 result = {}", userPagingRepository.save(new User("阿三", 12,"f@qq.com")));
logger.info("新增数据 result = {}", userPagingRepository.save(new User("张三", 12,"g@qq.com")));
logger.info("新增数据 result = {}", userPagingRepository.save(new User("米二", 8,"h@qq.com")));
}
@Test
public void find(){
logger.info("通过姓名查找(findByName) result = {}", userPagingRepository.findByName("张三"));
logger.info("通过姓名查找(queryByName) result = {}", userPagingRepository.queryByName("张三"));
logger.info("通过姓名或者邮箱(findByNameOrEmail) 查找 result = {}", userPagingRepository.findByNameOrEmail("张三","f@qq.com"));
logger.info("通过某一个 age 的数量(countByAge) result = {}", userPagingRepository.countByAge(12));
}
}
@Before会在@test之前运行。
输出日志：
Hibernate: select user0_.id as id1_0_, user0_.age as age2_0_, user0_.email as email3_0_, user0_.name as name4_0_ from user user0_ where user0_.name=?
通过姓名查找(findByName) result = [User{id=2, name='张三', age=16, email='b@qq.com'}, User{id=6, name='张三', age=12, email='g@qq.com'}]
Hibernate: select user0_.id as id1_0_, user0_.age as age2_0_, user0_.email as email3_0_, user0_.name as name4_0_ from user user0_ where user0_.name=?
通过姓名查找(queryByName) result = [User{id=2, name='张三', age=16, email='b@qq.com'}, User{id=6, name='张三', age=12, email='g@qq.com'}]
Hibernate: select user0_.id as id1_0_, user0_.age as age2_0_, user0_.email as email3_0_, user0_.name as name4_0_ from user user0_ where user0_.name=? or user0_.email=?
通过姓名或者邮箱(findByNameOrEmail) 查找 result = [User{id=2, name='张三', age=16, email='b@qq.com'}, User{id=5, name='阿三', age=12, email='f@qq.com'}, User{id=6, name='张三', age=12, email='g@qq.com'}]
Hibernate: select count(user0_.id) as col_0_0_ from user user0_ where user0_.age=?
通过某一个 age 的数量(countByAge) result = 3
日志比较冗余删除了多余日志，从日志中我们可以发现 JPA 根据我们定义的接口方法自动解析成 SQL
方法中支持的关键字如下
| 关键字 | 示例 | JPQL 表达式 |
|---|---|---|
And |
findByLastnameAndFirstname |
… where x.lastname = ?1 and x.firstname = ?2 |
Or |
findByLastnameOrFirstname |
… where x.lastname = ?1 or x.firstname = ?2 |
Is, Equals
|
findByFirstname,findByFirstnameIs,findByFirstnameEquals
|
… where x.firstname = ?1 |
Between |
findByStartDateBetween |
… where x.startDate between ?1 and ?2 |
LessThan |
findByAgeLessThan |
… where x.age < ?1 |
LessThanEqual |
findByAgeLessThanEqual |
… where x.age <= ?1 |
GreaterThan |
findByAgeGreaterThan |
… where x.age > ?1 |
GreaterThanEqual |
findByAgeGreaterThanEqual |
… where x.age >= ?1 |
After |
findByStartDateAfter |
… where x.startDate > ?1 |
Before |
findByStartDateBefore |
… where x.startDate < ?1 |
IsNull, Null
|
findByAge(Is)Null |
… where x.age is null |
IsNotNull, NotNull
|
findByAge(Is)NotNull |
… where x.age not null |
Like |
findByFirstnameLike |
… where x.firstname like ?1 |
NotLike |
findByFirstnameNotLike |
… where x.firstname not like ?1 |
StartingWith |
findByFirstnameStartingWith |
… where x.firstname like ?1 (parameter bound with appended %) |
EndingWith |
findByFirstnameEndingWith |
… where x.firstname like ?1 (parameter bound with prepended %) |
Containing |
findByFirstnameContaining |
… where x.firstname like ?1 (parameter bound wrapped in %) |
OrderBy |
findByAgeOrderByLastnameDesc |
… where x.age = ?1 order by x.lastname desc |
Not |
findByLastnameNot |
… where x.lastname <> ?1 |
In |
findByAgeIn(Collection ages) |
… where x.age in ?1 |
NotIn |
findByAgeNotIn(Collection ages) |
… where x.age not in ?1 |
True |
findByActiveTrue() |
… where x.active = true |
False |
findByActiveFalse() |
… where x.active = false |
IgnoreCase |
findByFirstnameIgnoreCase |
… where UPPER(x.firstame) = UPPER(?1) |
分页和排序
数据分页和排序在日常也是必不可少的，在 Spring Boot Jpa 中使用分页和排序，需要在Repository 接口的方法中，传入Pageable 实例 。
public interface UserPagingRepository extends PagingAndSortingRepository<User, Long> {
// 通过姓名条件查询
List<User> findByName(String name, Pageable pageable);
}
测试方法
@Test
public void pageAndSort(){
Sort sort = new Sort(Sort.Direction.DESC, "age");
int page = 0;
int size = 10;
Pageable pageable = PageRequest.of(page, size, sort);
logger.info("条件查询 result = {}", userPagingRepository.findByName("张三",pageable));
logger.info("---------------------------------");
logger.info("根据年龄排序 result = {}", userPagingRepository.findAll(sort));
}
测试结果
2020-02-29 17:02:37.431 INFO 48944 --- [ main] c.m.c.r.UserPagingRepositoryTest : 条件查询 result = [User{id=2, name='张三', age=16, email='b@qq.com'}, User{id=6, name='张三', age=12, email='g@qq.com'}]
2020-02-29 17:02:37.431 INFO 48944 --- [ main] c.m.c.r.UserPagingRepositoryTest : ---------------------------------
Hibernate: select user0_.id as id1_0_, user0_.age as age2_0_, user0_.email as email3_0_, user0_.name as name4_0_ from user user0_ order by user0_.age desc
2020-02-29 17:02:37.459 INFO 48944 --- [ main] c.m.c.r.UserPagingRepositoryTest : 根据年龄排序 result = [User{id=2, name='张三', age=16, email='b@qq.com'}, User{id=4, name='米二', age=13, email='e@qq.com'}, User{id=3, name='三哥', age=12, email='c@qq.com'}, User{id=5, name='阿三', age=12, email='f@qq.com'}, User{id=6, name='张三', age=12, email='g@qq.com'}, User{id=1, name='小米', age=9, email='a@qq.com'}, User{id=7, name='米二', age=8, email='h@qq.com'}]
复杂条件查询
前面演示了 CrudRepository 和 PagingAndSortingRepository ，下面通过继承 JpaRepository 和JpaSpecificationExecutor 操作更复杂的语句。
JpaSpecificationExecutor 是 JPA 2.0 提供的Criteria API，可以用于动态生成query。Spring Data JPA 支持 Criteria 查询，可以很方便地使用，足以应付工作中的所有复杂查询的情况了，可以对 JPA 实现最大限度的扩展。《spring data Jpa 从入门到精通》
public interface JpaSpecificationExecutor<T> {
// 根据 Specification 条件查询单个对象
Optional<T> findOne(@Nullable Specification<T> var1);
// 根据 Specification 条件查询 返回 List 结果
List<T> findAll(@Nullable Specification<T> var1);
// 根据 Specification 条件 和 分页条件查询
Page<T> findAll(@Nullable Specification<T> var1, Pageable var2);
// 根据 Specification 条件 和 排序条件查询 返回 List 结果
List<T> findAll(@Nullable Specification<T> var1, Sort var2);
// 根据 Specification 条件查询数量
long count(@Nullable Specification<T> var1);
}
UserJpaRepository 数据层接口
public interface UserJpaRepository extends JpaRepository<User,Long>, JpaSpecificationExecutor {
}
测试类
路径：src/test/java/com/mtcarpenter/chapter2/repository/UserJpaRepositoryTest.java
@RunWith(SpringRunner.class)
@SpringBootTest
public class UserJpaRepositoryTest {
@Test
public void specification() {
Specification specification = new Specification<User>() {
@Override
public Predicate toPredicate(Root root, CriteriaQuery query, CriteriaBuilder cb) {
// like 模糊查询 ， root.get("name") 属性名 "%三%" 为三
Predicate p1 = cb.like(root.get("name"), "%三%");
// greaterThan 表示 age 大于 10
Predicate p2 = cb.greaterThan(root.get("age"), 10);
// cb.and(p1, p2) ，and 则表示 p1 和 p2 并且关系，除了 and 还有or, not等。点击 CriteriaBuilder 可进行查看
return cb.and(p1, p2);
}
};
}
@Test
public void ConditionalQuery() {
int page = 0;
int size = 10;
Pageable pageable = PageRequest.of(page, size);
// 模拟传入的条件
User user = new User("三", 10, "b@qq.com");
Specification specification = new Specification<User>() {
@Override
public Predicate toPredicate(Root<User> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
List<Predicate> predicates = new ArrayList<>();
// 判断传入的值是否为空
if (!"".equals(user.getName())) {
predicates.add(cb.like(root.get("name"), "%" + user.getName() + "%"));
}
// 判断年龄是否为空
if (user.getAge() != null) {
predicates.add(cb.greaterThan(root.get("age"), user.getAge()));
}
return cb.and(predicates.toArray(new Predicate[predicates.size()]));
}
};
Page result = userJpaRepository.findAll(specification, pageable);
logger.info("条件查询 result = {}", result.getContent());
}
}
specification() 方法更容易理解，如果看懂了此方法，有利于更了解ConditionalQuery() 方法。ConditionalQuery() 方法这种模式也是在实际开发中，使用的频率比较高的方法。
JpaSpecificationExecutor 通过 CriteriaQuery 几乎可以实现任何逻辑了。