一、JPA
Spring Data JPA 是Spring Data 的一个子项目，它通过提供基于JPA的Repository极大了减少了操作JPA的代码。Spring Data JPA旨在通过减少实际需要的数量来显着提高数据访问层的实现。
在Spring环境中需要配置大量的XML配置，但是SpringBoot基本上帮助我们配置好了，我们只需要简单地配置一下DataSource和几项jpa额外的配置就完成了整个配置持久化层的工作。EntityManagerFactory 那些都不用配置了。
JPA不是一种框架，而只是一种ORM规范，而这种规范具体由其他厂商来实现，其中最熟悉的莫过于Hibernate了。
网络上对JPA的褒贬不一，特别是用JPA进行多表操作的时候，确实是比较繁琐。当然任何技术有好的方面也有坏的方面，本章重点不在于此。
二、添加依赖
<!-- jpa依赖 -->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<!-- mysql依赖 -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
</dependency>
三、数据源和JPA配置
spring.datasource.driver-class-name=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql:///springboot
spring.datasource.username=root
spring.datasource.password=admin
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true
四、JPA查询语法
三、数据源和JPA配置
spring.datasource.driver-class-name=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql:///springboot
spring.datasource.username=root
spring.datasource.password=admin
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql:///springboot
spring.datasource.username=root
spring.datasource.password=admin
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true
4.1、JPA内置方法
Repository JPA基层接口
public interface Repository<T, ID extends Serializable> {}
CrudRepository 专门用于crud 接口
public interface CrudRepository<T, ID extends Serializable> extends Repository<T, ID> {
<S extends T> S save(S entity);
<S extends T> Iterable<S> save(Iterable<S> entities);
T findOne(ID id);
boolean exists(ID id);
Iterable<T> findAll();
Iterable<T> findAll(Iterable<ID> ids);
long count();
void delete(ID id);
void delete(T entity);
void delete(Iterable<? extends T> entities);
void deleteAll();
}
PagingAndSortingRepository 带有简单的分页和排序的接口
public interface PagingAndSortingRepository<T, ID extends Serializable> extends CrudRepository<T, ID> {
Iterable<T> findAll(Sort sort);
Page<T> findAll(Pageable pageable);
}
PagingAndSortingRepository内部有两个重要的类，分别是Sort类和Pageable接口，定义如下：
//排序类
public class Sort implements Iterable<org.springframework.data.domain.Sort.Order>, Serializable {
//默认以升序排序
public static final Direction DEFAULT_DIRECTION = Direction.ASC;
private final List<Order> orders;
public Sort(Order... orders) {
this(Arrays.asList(orders));
}
public Sort(List<Order> orders) {
if (null == orders || orders.isEmpty()) {
throw new IllegalArgumentException("You have to provide at least one sort property to sort by!");
}
this.orders = orders;
}
public Sort(String... properties) {
this(DEFAULT_DIRECTION, properties);
}
public Sort(Direction direction, String... properties) {
this(direction, properties == null ? new ArrayList<String>() : Arrays.asList(properties));
}
public Sort(Direction direction, List<String> properties) {
if (properties == null || properties.isEmpty()) {
throw new IllegalArgumentException("You have to provide at least one property to sort by!");
}
this.orders = new ArrayList<Order>(properties.size());
for (String property : properties) {
this.orders.add(new Order(direction, property));
}
}
public Sort and(Sort sort) {
if (sort == null) {
return this;
}
ArrayList<Order> these = new ArrayList<Order>(this.orders);
for (Order order : sort) {
these.add(order);
}
return new Sort(these);
}
public Order getOrderFor(String property) {
for (Order order : this) {
if (order.getProperty().equals(property)) {
return order;
}
}
return null;
}
//other...
//内部定义了一个Direction的枚举类
public static enum Direction {
ASC, DESC;
//other code...
}
//内部定义了Order类，用于字段排序
public static class Order implements Serializable {
private static final boolean DEFAULT_IGNORE_CASE = false;
private final Direction direction;
private final String property;
private final boolean ignoreCase;
private final NullHandling nullHandling;
public Order(Direction direction, String property) {
this(direction, property, DEFAULT_IGNORE_CASE, null);
}
public Order(Direction direction, String property, NullHandling nullHandlingHint) {
this(direction, property, DEFAULT_IGNORE_CASE, nullHandlingHint);
}
public Order(String property) {
this(DEFAULT_DIRECTION, property);
}
private Order(Direction direction, String property, boolean ignoreCase, NullHandling nullHandling) {
if (!StringUtils.hasText(property)) {
throw new IllegalArgumentException("Property must not null or empty!");
}
this.direction = direction == null ? DEFAULT_DIRECTION : direction;
this.property = property;
this.ignoreCase = ignoreCase;
this.nullHandling = nullHandling == null ? NullHandling.NATIVE : nullHandling;
}
//other...
}
}
//分页接口
public interface Pageable {
int getPageNumber();
int getPageSize();
int getOffset();
Sort getSort();
Pageable next();
Pageable previousOrFirst();
Pageable first();
boolean hasPrevious();
}
//分页抽象类
public abstract class AbstractPageRequest implements Pageable, Serializable {
private final int page;
private final int size;
public AbstractPageRequest(int page, int size) {
//other code...
this.page = page;
this.size = size;
}
public int getPageSize() {
return size;
}
public int getPageNumber() {
return page;
}
public int getOffset() {
return page * size;
}
public boolean hasPrevious() {
return page > 0;
}
public Pageable previousOrFirst() {
return hasPrevious() ? previous() : first();
}
public abstract Pageable next();
public abstract Pageable previous();
public abstract Pageable first();
//other code...
}
//分页实现类
public class PageRequest extends AbstractPageRequest {
private final Sort sort;
public PageRequest(int page, int size) {
this(page, size, null);
}
public PageRequest(int page, int size, Direction direction, String... properties) {
this(page, size, new Sort(direction, properties));
}
public PageRequest(int page, int size, Sort sort) {
super(page, size);
this.sort = sort;
}
public Sort getSort() {
return sort;
}
public Pageable next() {
return new PageRequest(getPageNumber() + 1, getPageSize(), getSort());
}
public PageRequest previous() {
return getPageNumber() == 0 ? this : new PageRequest(getPageNumber() - 1, getPageSize(), getSort());
}
public Pageable first() {
return new PageRequest(0, getPageSize(), getSort());
}
//other code...
}
JpaRepository 带有crud接口和分页、排序的接口
public interface JpaRepository<T, ID extends Serializable>
extends PagingAndSortingRepository<T, ID>, QueryByExampleExecutor<T> {
List<T> findAll();
List<T> findAll(Sort sort);
List<T> findAll(Iterable<ID> ids);
<S extends T> List<S> save(Iterable<S> entities);
void flush();
<S extends T> S saveAndFlush(S entity);
void deleteInBatch(Iterable<T> entities);
void deleteAllInBatch();
T getOne(ID id);
@Override
<S extends T> List<S> findAll(Example<S> example);
@Override
<S extends T> List<S> findAll(Example<S> example, Sort sort);
}
JpaSpecificationExecutor 用于复杂的条件查询并分页、排序功能
public interface JpaSpecificationExecutor<T> {
T findOne(Specification<T> spec);
List<T> findAll(Specification<T> spec);
Page<T> findAll(Specification<T> spec, Pageable pageable);
List<T> findAll(Specification<T> spec, Sort sort);
long count(Specification<T> spec);
}
public interface Specification<T> {
Predicate toPredicate(Root<T> root, CriteriaQuery<?> query, CriteriaBuilder cb);
}
public class Specifications<T> implements Specification<T>, Serializable {
private final Specification<T> spec;
private Specifications(Specification<T> spec) {
this.spec = spec;
}
public static <T> Specifications<T> where(Specification<T> spec) {
return new Specifications<T>(spec);
}
public Specifications<T> and(Specification<T> other) {
return new Specifications<T>(new ComposedSpecification<T>(spec, other, AND));
}
public Specifications<T> or(Specification<T> other) {
return new Specifications<T>(new ComposedSpecification<T>(spec, other, OR));
}
public static <T> Specifications<T> not(Specification<T> spec) {
return new Specifications<T>(new NegatedSpecification<T>(spec));
}
public Predicate toPredicate(Root<T> root, CriteriaQuery<?> query, CriteriaBuilder builder) {
return spec == null ? null : spec.toPredicate(root, query, builder);
}
//other code...
}
以上一大堆JPA内置方法，可以直接使用，而无需再声明定义了。当然如果想重载或者自定义的话，可以重新声明定义下。
5.2、通过解析方法名创建查询
| Keyword | Sample | JPQL snippet |
|---|---|---|
| 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 | findByAgeIsNull | … 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 |
| EndingWith | findByFirstnameEndingWith | … where x.firstname like ?1 |
| Containing | findByFirstnameContaining | … where x.firstname like ?1 |
| OrderBy | findByAgeOrderByLastnameDesc | … where x.age = ?1 order by x.lastname desc |
| Not | findByLastnameNot | … where x.lastname <> ?1 |
| In | findByAgeIn(Collection<Age> ages) | … where x.age in ?1 |
| NotIn | findByAgeNotIn(Collection<Age> age) | … 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) |
例如：
- findByLastName(String lastName)：表示根据lastName精确查询
- findByLastNameLike(String lastName)：表示根据lastName模糊查询
- findByAgeBetween(int min, int max)：表示查询年龄在[min,max]之间的数据
- findByAgeEquals(int age)：表示查询年龄等于age的数据
- findByAgeAndGender(int age, String gender)：表示根据年龄等于age且性别为gender的数据
- 等等...
4.3、使用自定义的@Query注解进行查询
//使用自定义的@Query注解，实现sql语句
@Query("select count(*) from Person")
Long findAllCount();
@Query("from Person where id = ?1")
List<Person> selectWhereById(Integer id);
@Query("delete from Person where id = ?1")
@Modifying
void deleteById(Integer id);
@Query(value="select distinct id from person", nativeQuery = true)
List<Integer> getIds();
注意：
- 使用@Modifying注解表示该Query是个增删改的操作，需要事务管理。
- 指定nativeQuery=true，则说明该Query的sql语句为原生SQL，而不是hql，默认为false，即使用hql查询。
五、JPA常用注解
- @Entity：设置Pojo为实体
- @Table：设置表名
- @Id：设置主键
-
@Column：设置普通列名
- name：字段名，默认为空串
- unique：是否唯一，默认为false
- nullable：是否可以为空，默认为true
- insertable：是否可插入，默认为true
- updatable：是否可更新，默认为true
- length：列值最大长度，默认为255
- precision：精度，即数字长度，默认为0
- scale：小数点后位数，默认为0
- @GeneratedValue：主键生成策略，有AUTO, TABLE, SEQUENCE, IDENTITY四种属性值
- @SequenceGenerator：按照序列生成主键的序列名
- @Transient：临时字段，不需要跟数据库映射的字段
- @Temporal：时间格式，有DATE, TIME, TIMESTAMP三种属性值
- @Embedded：注解属性，用来表示该属性的类是个嵌入类，同时嵌入类必须使用@Embeddable注解
- @Embeddable：注解类，表示该类是个嵌入类，会被嵌入到其他类中
-
@JoinColumn：定义外键列的属性
- name：外键列的名称
- referencedColumnName：参考列，默认值为关联表的主键。
- @OneToOne：定义1-1的关联关系
- @OneToMany：定义1-n的关联关系
- @ManyToOne：定义n-1的关联关系
-
@ManyToMany：定义n-n的关联关系
- cascade：关联属性，这个属性定义了当前类对象操作了之后，级联对象的操作。有ALL，PERSIST，MERGE，REMOVE，REFRESH，DETACH六种属性值。
- fetch：级联数据加载策略
- LAZY：表示关系类在被访问时才被加载（默认）
- EAGER：表示关系类在主类加载的时候同时加载
- mappedBy：拥有关联关系的域，如果关系是单向的就不需要。双向关系表，那么拥有关系的这一方有建立、解除和更新与另一方关系的能力，而另一方没有，只能被动管理，这个属性被定义在关系的被拥有方。双向@OneToOne，双向@OneToMany，双向@ManyToMany中均需要有此属性。注意点：该属性与@JoinColumn互斥，不能同时出现在类的属性上。
具体注解使用请参看我的GitHub-java-jpa或者码云-java-jpa。
六、使用JPA操作数据库
附上代码：
实体类Person
@Entity
@Table
public class Person implements Serializable{
@Id
@GeneratedValue
private Integer id;
private String name;
private int age;
//getter和setter
}
控制器类PersonController
@RestController
@RequestMapping("/person")
public class PersonController {
@Autowired
private IPersonService personService;
@RequestMapping("/find")
public Person findPersonByName(String name){
return personService.findPersonByName(name);
}
@PostMapping("/")
public String insertIntoPerson(Person person){
personService.insertIntoPerson(person);
return "success";
}
@GetMapping("/age")
public List<Person> getPersonAgeBetween(int min, int max){
return personService.getPersonAgeBetween(min, max);
}
@GetMapping("/page")
public Page<Person> getPersonsByPage(int pageNum, int pageSize){
return personService.getPersonsByPage(pageNum, pageSize);
}
@GetMapping("/sort")
public Page<Person> getPersonsBySortAge(){
return personService.getPersonsBySortAge();
}
@GetMapping("/count")
public Long getAllCount(){
return personService.findAllCount();
}
@PostMapping("/update")
public void updateOnePerson(Person person){
personService.updateOnePerson(person.getAge(), person.getName(), person.getId());
}
@GetMapping("/ids")
public List<Integer> getIds(){
return personService.getIds();
}
}
业务层接口IPersonService
public interface IPersonService {
Person findPersonByName(String name);
void insertIntoPerson(Person person);
List<Person> getPersonAgeBetween(int min, int max);
Page<Person> getPersonsByPage(int pageNum, int pageSize);
Page<Person> getPersonsBySortAge();
Long findAllCount();
void updateOnePerson(int age, String name, int id);
List<Integer> getIds();
}
业务层接口实现类PersonServiceImpl
@Service
public class PersonServiceImpl implements IPersonService {
@Autowired
private IPersonRepository personRepository;
@Override
public Person findPersonByName(String name) {
return personRepository.findPersonByName(name);
}
@Override
public void insertIntoPerson(Person person) {
personRepository.save(person);
}
@Override
public List<Person> getPersonAgeBetween(int min, int max) {
return personRepository.findPersonByAgeBetween(min, max);
}
@Override
public Page<Person> getPersonsByPage(int pageNum, int pageSize) {
Pageable pageable = new PageRequest(pageNum, pageSize);
return personRepository.findAll(pageable);
}
@Override
public Page<Person> getPersonsBySortAge() {
Sort sort = new Sort(new Sort.Order(Sort.Direction.ASC, "age"));
Pageable pageable = new PageRequest(0,5, sort);
return personRepository.findAll(pageable);
}
@Override
public Long findAllCount() {
return personRepository.findAllCount();
}
@Transactional
@Override
public void updateOnePerson(int age, String name, int id){
personRepository.updateOnePerson(age, name, id);
}
@Override
public List<Integer> getIds() {
return personRepository.getIds();
}
}
持久化接口IPersonRepository
public interface IPersonRepository extends JpaRepository<Person, Integer>{
Person findPersonByName(String name);
List<Person> findPersonByAgeBetween(int min, int max);
//使用自定义的@Query注解，实现sql语句
@Query("select count(*) from Person")
Long findAllCount();
//使用@Modifying注解表示该hql是个增删改的操作，需要事务管理
@Query("update Person set age = ?1, name = ?2 where id = ?3")
@Modifying
void updateOnePerson(int age, String name, int id);
//原生SQL
@Query(value="select distinct id from person", nativeQuery = true)
List<Integer> getIds();
}
