Spring Data JPA - 中文手冊(cè)

參考文檔：
http://blog.csdn.net/liuchuanhong1/article/details/70244261?utm_source=gold_browser_extension
https://docs.spring.io/spring-data/jpa/docs/1.11.9.RELEASE/reference/html/#specifications
https://www.v2ex.com/t/350737

項(xiàng)目中使用spring data jpa

@EnableJpaRepositories
class Config {}

查詢方法的生成策略 Query lookup strategies

• CREATE 根據(jù)方法的名字直接創(chuàng)建對(duì)應(yīng)的查詢語(yǔ)句
• USE_DECLARED_QUERY 使用聲明的查詢語(yǔ)句了罪，如果每一找到聲明的語(yǔ)句將會(huì)拋出一個(gè)異常泊藕，聲明一個(gè)語(yǔ)句使用 @NamedQuery
• CREATE_IF_NOT_FOUND 首先查找是否已經(jīng)有聲明的查詢語(yǔ)句娃圆，如果每一再創(chuàng)建蛾茉，這是默認(rèn)的策略

通過(guò)方法名來(lái)定義語(yǔ)句

public interface PersonRepository extends Repository<User, Long> {

  // 使用 distinct 關(guān)鍵字
  List<Person> findDistinctPeopleByLastnameOrFirstname(String lastname, String firstname);
  List<Person> findPeopleDistinctByLastnameOrFirstname(String lastname, String firstname);

  // 忽略大小寫(xiě)進(jìn)行匹配 IgnoreCase
  List<Person> findByLastnameIgnoreCase(String lastname);
  // 對(duì)所有的查詢條件進(jìn)行忽略大小寫(xiě)進(jìn)行匹配 IgnoreCase
  List<Person> findByLastnameAndFirstnameAllIgnoreCase(String lastname, String firstname);

  // Order By 語(yǔ)句
  List<Person> findByLastnameOrderByFirstnameAsc(String lastname);
  List<Person> findByLastnameOrderByFirstnameDesc(String lastname);
  
  //Person 中有個(gè)Address, Address中有zipCode屬性悦屏，直接通過(guò)zipCode來(lái)查詢Persion
  List<Person> findByAddressZipCode(ZipCode zipCode);
  //和上面的方法完成同樣的功能础爬， 使用 _ 可以用來(lái)區(qū)分屬性，避免生成錯(cuò)誤的語(yǔ)句
  List<Person> findByAddress_ZipCode(ZipCode zipCode);
  
  
  //限制返回?cái)?shù)據(jù)的條數(shù) Limiting query results
  User findFirstByOrderByLastnameAsc();
  User findTopByOrderByAgeDesc();
  
  Page<User> queryFirst10ByLastname(String lastname, Pageable pageable);
  Slice<User> findTop3ByLastname(String lastname, Pageable pageable);
  
  List<User> findFirst10ByLastname(String lastname, Sort sort);
  List<User> findTop10ByLastname(String lastname, Pageable pageable);
  
  //異步查詢，調(diào)用查詢方法后立即返回 Async query results
  @Async
  Future<User> findByFirstname(String firstname);
  @Async
  CompletableFuture<User> findOneByFirstname(String firstname);
  @Async
  ListenableFuture<User> findOneByLastname(String lastname);    
}

為所有生成的Repository添加一些額外的方法

1. 聲明一個(gè)接口常熙，定義出需要添加的方法

@NoRepositoryBean
public interface MyRepository<T, ID extends Serializable>
  extends PagingAndSortingRepository<T, ID> {

  void sharedCustomMethod(ID id);
}

2. 實(shí)現(xiàn)定義的接口

public class MyRepositoryImpl<T, ID extends Serializable>
  extends SimpleJpaRepository<T, ID> implements MyRepository<T, ID> {

  private final EntityManager entityManager;

  public MyRepositoryImpl(JpaEntityInformation entityInformation,
                          EntityManager entityManager) {
    super(entityInformation, entityManager);

    // Keep the EntityManager around to used from the newly introduced methods.
    this.entityManager = entityManager;
  }

  public void sharedCustomMethod(ID id) {
    // implementation goes here
  }
}

3.配置實(shí)現(xiàn)類

@Configuration
@EnableJpaRepositories(repositoryBaseClass = MyRepositoryImpl.class)
class ApplicationConfiguration { … }

Web support

@Configuration
@EnableWebMvc
@EnableSpringDataWebSupport
class WebConfiguration { }

@EnableSpringDataWebSupport 將會(huì)開(kāi)啟一些組件，具體可以打開(kāi)源碼查看

• PageableHandlerMethodArgumentResolver 通過(guò)參數(shù)可以自動(dòng)注入 Pageable 對(duì)象到控制器
  page -> Page you want to retrieve, 0 indexed and defaults to 0. |
  size -> Size of the page you want to retrieve, defaults to 20. |

• SortHandlerMethodArgumentResolver 通過(guò)參數(shù)可以自動(dòng)注入 Sort 對(duì)象到控制器
  sort -> Properties that should be sorted by in the format property,property(,ASC|DESC). Default sort direction is ascending. Use multiple sort parameters if you want to switch directions, e.g. ?sort=firstname&sort=lastname,asc. |

• DomainClassConverter 傳入一個(gè)對(duì)象Id 就可以直接轉(zhuǎn)換成 需要對(duì)象

 @Controller
    @RequestMapping("/users")
    public class UserController {
    
      @Autowired UserRepository repository;
    
      @RequestMapping
      public String showUsers(Model model, Pageable pageable) {
    
        model.addAttribute("users", repository.findAll(pageable));
        return "users";
      }
    }

如果在需要注入對(duì)個(gè)Pageable對(duì)象到controller中，可以使用@Qualifier來(lái)定義前綴聋袋，下劃線分隔穴吹，eg: foo_page=1

public String showUsers(Model model,
      @Qualifier("foo") Pageable first,
      @Qualifier("bar") Pageable second) { … }

@PageableDefault 配置默認(rèn)的分頁(yè)港令，如果前端沒(méi)有傳入分頁(yè)信息顷霹，可以使用來(lái)設(shè)置默認(rèn)的分頁(yè)淋淀，默認(rèn)是 new PageRequest(0, 20)

Supported keywords inside method names

使用@Query來(lái)聲明語(yǔ)句

public interface UserRepository extends JpaRepository<User, Long> {

  @Query(value = "SELECT * FROM USERS WHERE LASTNAME = ?1",
    countQuery = "SELECT count(*) FROM USERS WHERE LASTNAME = ?1",
    nativeQuery = true)
  Page<User> findByLastname(String lastname, Pageable pageable);
}

Using SpEL expressions

public interface UserRepository extends JpaRepository<User,Long> {

  @Query("select u from #{#entityName} u where u.lastname = ?1")
  List<User> findByLastname(String lastname);
}

entityName 表示實(shí)體類的名字

使用查詢提示徽缚，具體的查詢提示的值是根據(jù)JPA底層實(shí)習(xí)框架提供的

public interface UserRepository extends Repository<User, Long> {

  @QueryHints(value = { @QueryHint(name = "name", value = "value")},
              forCounting = false)
  Page<User> findByLastname(String lastname, Pageable pageable);
}

自定義查詢返回的返回結(jié)果

1. 通過(guò)定義接口的方式來(lái)返回?cái)?shù)據(jù)

假如實(shí)體對(duì)象：

class Person {
  @Id UUID id;
  String firstname, lastname;
  Address address;

  static class Address {
    String zipCode, city, street;
  }
}

可以這樣定義一個(gè)接口：

interface PersonSummary {
  String getFirstname();
  String getLastname();
  AddressSummary getAddress();

  interface AddressSummary {
    String getCity();
  }
}

查詢方法的定義：

interface PersonRepository extends Repository<Person, UUID> {
  Collection<PersonSummary> findByLastname(String lastname);
}

這樣就可以完成自定義查詢凿试，還有其他方式定義接口

interface NamesOnly {

  @Value("#{target.firstname + ' ' + target.lastname}")
  String getFullName();
  …
}

組合了firstname lastname, 返回的對(duì)象將會(huì)用 target 變量替代那婉。如果想要做更加復(fù)雜的編程可以使用下面的方法详炬，使用default定義一個(gè)方法

interface NamesOnly {

  String getFirstname();
  String getLastname();

  default String getFullName() {
    //定義自己的邏輯實(shí)現(xiàn)，可以通過(guò)ApplicationContext 來(lái)獲取bean對(duì)象來(lái)調(diào)用方法
    return getFirstname.concat(" ").concat(getLastname());
  }
}

調(diào)用容器中的Bean來(lái)返回結(jié)果的另一種方式@myBean

@Component
class MyBean {

  String getFullName(Person person) {
    …
  }
}

interface NamesOnly {

  @Value("#{@myBean.getFullName(target)}")
  String getFullName();
  …
}

如果想要使用 方法中的參數(shù)可以用這種方式

interface NamesOnly {

  @Value("#{args[0] + ' ' + target.firstname + '!'}")
  String getSalutation(String prefix);
}

args[i] i 表示方法中的第幾個(gè)

2. 通過(guò)定義DTO的方式來(lái)返回?cái)?shù)據(jù)

這種方式底層會(huì)根據(jù)DTO暴露的構(gòu)造放的參數(shù)名字來(lái)加載 需要的字段
定義的DTO

class NamesOnly {
  private final String firstname, lastname;

  NamesOnly(String firstname, String lastname) {
    this.firstname = firstname;
    this.lastname = lastname;
  }
  String getFirstname() {
    return this.firstname;
  }
  String getLastname() {
    return this.lastname;
  }
  // equals(…) and hashCode() implementations
}

定義的Repository

interface PersonRepository extends Repository<Person, UUID> {
  Collection<T> findByLastname(String lastname, Class<T> type);
}

使用方式如下：

void someMethod(PersonRepository people) {
  Collection<Person> aggregates = people.findByLastname("Matthews", Person.class);
  Collection<NamesOnly> aggregates = people.findByLastname("Matthews", NamesOnly.class);
}

存儲(chǔ)過(guò)程的使用

參考：https://docs.spring.io/spring-data/jpa/docs/1.11.9.RELEASE/reference/html/#jpa.stored-procedures

Specifications

public class CustomerSpecs {

  public static Specification<Customer> isLongTermCustomer() {
    return new Specification<Customer>() {
      public Predicate toPredicate(Root<Customer> root, CriteriaQuery<?> query,
            CriteriaBuilder builder) {

         LocalDate date = new LocalDate().minusYears(2);
         return builder.lessThan(root.get(_Customer.createdAt), date);
      }
    };
  }

  public static Specification<Customer> hasSalesOfMoreThan(MontaryAmount value) {
    return new Specification<Customer>() {
      public Predicate toPredicate(Root<T> root, CriteriaQuery<?> query,
            CriteriaBuilder builder) {

         // build query here
      }
    };
  }
}

List<Customer> customers = customerRepository.findAll(isLongTermCustomer());

Locking

interface UserRepository extends Repository<User, Long> {
  // Plain query method
  @Lock(LockModeType.READ)
  List<User> findByLastname(String lastname);
}

Auditing

提供的注解猫妙，在實(shí)體中添加：
@CreatedBy, @LastModifiedBy, @CreatedDate, @LastModifiedDate

實(shí)現(xiàn)接口AuditorAware 為 @CreatedBy, @LastModifiedBy 設(shè)置值

class SpringSecurityAuditorAware implements AuditorAware<User> {
  public User getCurrentAuditor() {
    Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
    if (authentication == null || !authentication.isAuthenticated()) {
      return null;
    }
    return ((MyUserDetails) authentication.getPrincipal()).getUser();
  }
}

最后在實(shí)體上添加注解@EntityListeners(AuditingEntityListener.class)

@Entity
@EntityListeners(AuditingEntityListener.class)
public class MyEntity {
}

獲取 EntityManager 對(duì)象

可以使用@PersistenceContext. spring data jpa 還提供了一種方式：

class UserRepositoryImpl implements UserRepositoryCustom {
  private final EntityManager em;
  @Autowired
  public UserRepositoryImpl(JpaContext context) {
    this.em = context.getEntityManagerByManagedType(User.class);
  }
}

https://docs.spring.io/spring-data/jpa/docs/1.11.9.RELEASE/reference/html/#appendix

更多spring 相關(guān)文章：
http://blog.xianshiyue.com/tag/springboot/
http://blog.xianshiyue.com/tag/spring-cloud/
http://blog.xianshiyue.com/tag/springmvc/