前言
在實(shí)際項(xiàng)目中對(duì)Spring Data的各種使用相當(dāng)多，簡單的增刪改查Spring Data提供了現(xiàn)成的方法，一些復(fù)雜的，我們可以在接口方法寫And,Not等關(guān)鍵字來搞定，想寫原生SQL，CQL（Neo4j），Query DSL （Elasticsearch）的，直接使用@Query(“......”)注解搞定，真的是方便到不行！
當(dāng)我們執(zhí)行批量操作時(shí)，比如從數(shù)據(jù)庫中查找“Person”的所有實(shí)例或者根據(jù)國家查找每個(gè)人，我們經(jīng)常進(jìn)行分頁，以便我們可以向最終用戶提供一個(gè)小數(shù)據(jù)塊，并在下一個(gè)請求中，我們獲取下一個(gè)數(shù)據(jù)塊。
Spring Data為分頁提供支持。它創(chuàng)建了實(shí)現(xiàn)分頁的所有邏輯，例如所有頁面的行計(jì)數(shù)等等。
在Spring Data中實(shí)現(xiàn)分頁非常簡單。我們只需要按照以下步驟操作：
1.創(chuàng)建擴(kuò)展PagingAndSortingRepository的存儲(chǔ)庫。
@Repositorypublic interface PersonRepositary extends PagingAndSortingRepository<Person, Long>,QueryDslPredicateExecutor<Person> { @Query("select p from Person p where p.country like ?1 order by country") List<Person> findByCountryContains(String country); List<Person> findPersonByHobbyName(String name); @Query("select p from Person p where p.id = ?1 and country='America'") Person findOne(Long id);}2. 創(chuàng)建域?qū)ο蟆?/p>
@Entitypublic class Person { @Id @GeneratedValue(strategy=GenerationType.AUTO) private Long id; private String name; private String country; private String gender;@OneToMany(mappedBy="person",targetEntity=Hobby.class, fetch=FetchType.EAGER,cascade=CascadeType.ALL) List<Hobby> hobby;public String getName() { return name;}public void setName(String name) { this.name = name;}public String getCountry() { return country;}public void setCountry(String country) { this.country = country;}public String getGender() { return gender;}public void setGender(String gender) { this.gender = gender;}public Long getId() { return id;}public void setId(Long id) { this.id = id;}public List<Hobby> getHobby() { return hobby;}public void setHobby(List<Hobby> hobby) { this.hobby = hobby;}public void addHobby(Hobby ihobby){ if(hobby == null) { hobby = new ArrayList<Hobby>(); } hobby.add(ihobby);} @Override public String toString() { return "Person [id=" + id + ", name=" + name + ", country=" + country + ", gender=" + gender + "]"; }}3.獲取所有人員。創(chuàng)建一個(gè)限制為1的PageRequest對(duì)象并請求第一頁。
@SpringBootApplication@EnableJpaRepositories("com.example.repo")public class PersonApplication { @Autowired HobbyRepository hRepo; private static final Logger log = LoggerFactory.getLogger(PersonApplication.class); @Bean public CommandLineRunner demo(PersonRepositary repository) { findAll(repository); return null; } private PageRequest gotoPage(int page) { PageRequest request = new PageRequest(page,1) return request; } private void findAll(PersonRepositary repository) { Iterable<Person> pList = repository.findAll(gotoPage(0)); for(Person p : pList) log.info("Person " + p); } public static void main(String[] args) { SpringApplication.run(PersonApplication.class, args); }}運(yùn)行時(shí)SQL輸出：
Hibernate:
select
count(person0_.id) as col_0_0_
from
person person0_
Hibernate:
select
person0_.id as id1_1_,
person0_.country as country2_1_,
person0_.gender as gender3_1_,
person0_.name as name4_1_
from
person person0_ limit ?
Person Person [id=13, name=Samir mitra, country=America, gender=male]
分頁和排序代碼實(shí)現(xiàn)
要進(jìn)行排序，我們必須傳遞排序方向和排序字段以及頁碼和限制。假設(shè)我們想按國家名稱按升序排序 - 我們修改 goto 方法如下：
private PageRequest gotoPage(int page){ PageRequest request = new PageRequest(page,1,Sort.Direction.ASC,"country"); return request;}SQL輸出：
select
count(person0_.id) as col_0_0_
from
person person0_
Hibernate:
select
person0_.id as id1_1_,
person0_.country as country2_1_,
person0_.gender as gender3_1_,
person0_.name as name4_1_
from
person person0_
order by
person0_.country asc limit ?
總結(jié)
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