说老实话，Spring Data JPA很好用，上次使用还是2013年，当时只是完成Java Bean和数据库中表的映射。
最近想起来用Spring Data JPA的起因是手头有一个项目，源代码是用原生SQL+JDBC实现的，在第一次部署时要初始化数据库，还hardcode了很多数据库配置参数。正好最近有空，就打算用Spring Boot Data JPA（spring-boot-starter-data-jpa）改造一下，仔细看了一下源代码发现和几年前已经天差地别，如果你的业务逻辑不是特别复杂或者表结构设计合理，一行真正SQL逻辑实现都不要写，良心啊，真是为我这样的懒人着想啊。
首先开始写Repository，常见的用法有两种，一个是写一个接口继承JpaRepository，代码如下：
package com.company.inventory.repository;
import java.util.List;
import org.springframework.data.jpa.repository.JpaRepository;
import comcompany.inventory.model.Device;
public interface DeviceRepository extends JpaRepository<Device, Long> {
List<Device> findBySnOrderByGmtCreatedDesc(String sn);
}
另外一个是继承CrudRepository，代码如下：
package com.company.inventory.repository;
import java.util.List;
import org.springframework.data.repository.CrudRepository;
import comcompany.inventory.model.Device;
public interface DeviceRepository extends CrudRepository<Device, Long> {
List<Device> findBySnOrderByGmtCreatedDesc(String sn);
}
JpaRepository和CrudRepository关系如下：
public interface JpaRepository<T, ID> extends PagingAndSortingRepository<T, ID>, QueryByExampleExecutor<T>
public interface PagingAndSortingRepository<T, ID> extends CrudRepository<T, ID>
public interface CrudRepository<T, ID> extends Repository<T, ID>
从上面的关系就能看出JpaRepository除了能做CrudRepository能做的所有事外，还多了分页和排序功能以及QueryByExampleExecutor提供的QueryByExample功能。但是JpaRepository也和JPA持久化技术进行了绑定。http://jtuts.com/2014/08/26/difference-between-crudrepository-and-jparepository-in-spring-data-jpa/
所以建议尽量使用CrudRepository或者PagingAndSortingRepository
Supported keywords inside method names
| 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(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<Age> ages)
|
… where x.age in ?1
|
| NotIn
|
findByAgeNotIn(Collection<Age> 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)
|
接下来是定义Entity，遇到了第一个坑，代码如下：
package com.company.inventory.model;
import java.io.Serializable;
import java.util.Date;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
@Entity
@Table( name = "device" )
public class Device implements Serializable {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private Long id;
@Column(unique = true, nullable = false)
private String sn;
@Column(name = "gmtCreated", nullable = false)
private Date gmtCreated = new Date();
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public Date getGmtCreated() {
return gmtCreated;
}
public void setGmtCreated(Date gmtCreated) {
this.gmtCreated = gmtCreated;
}
}
第一个坑，该类必须是实体类，不能继承于任何基类，除非其中的参数不需要映射到数据库中。
例如有一个基类如下：
public class BaseModel{
protected String name;
//set, get方法忽略
}
public class Person extends BaseModel implements Serializable{
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private Long id;
}
name将不能映射到数据库中。
第二个坑，如果Field类似gmtCreated，有大写字母的，默认映射到数据库字段名会变为gmt_created。如果你的设计不是这样，而是直接映射不做修改。需要在application.properties中指定Naming strategy，否则默认是org.hibernate.boot.orm.jpa.hibernate.SpringPhysicalNamingStrategy，在进行领域映射时，首字母小写，大写字母变为下划线加小写。添加代码如下：
spring.jpa.hibernate.naming.physical-strategy = org.hibernate.boot.model.naming.PhysicalNamingStrategyStandardImpl
第三个坑，如果使用like，代码如下：
public Page<User> findUserByKey(String key, int page, int size){
Page<User> result = userRepository.findAll(new Specification<User> () {
public Predicate toPredicate(Root<User> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
Join<User, Role> join = root.join("role", JoinType.INNER);
Path<String> namePath = join.get("name");
Path<String> statusPath = root.get("status");
Path<String> usernamePath = root.get("username");
Path<String> nicknamePath = root.get("nickname");
Predicate or = cb.or(cb.like(namePath, key), cb.like(usernamePath, key), cb.like(nicknamePath, key));
return cb.and(or, cb.equal(statusPath, 0));
}
}, PageRequest.of(page - 1, size));
return result;
}
其中的key，必须是类似%abc%，而不是'%abc%'。
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