spring data jpa 通过创建方法名来做查询,只能做简单的查询,那如果我们要做复杂一些的查询呢,多条件分页怎么办,这里,spring data jpa为我们提供了JpaSpecificationExecutor接口,只要简单实现toPredicate方法就可以实现复杂的查询
1.首先让我们的接口继承于JpaSpecificationExecutor
public interface TaskDao extends JpaSpecificationExecutor<Task>{
}
2.JpaSpecificationExecutor提供了以下接口
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);
}
其中Specification就是需要我们传进去的参数,它是一个接口
public interface Specification<T> {
Predicate toPredicate(Root<T> root, CriteriaQuery<?> query, CriteriaBuilder cb);
}
提供唯一的一个方法toPredicate,我们只要按照JPA 2.0 criteria api写好查询条件就可以了,关于JPA 2.0 criteria api的介绍和使用,欢迎参考
http://blog.csdn.net/dracotianlong/article/details/28445725
http://developer.51cto.com/art/200911/162722.htm
2.接下来我们在service bean
@Service
public class TaskService {
@Autowired TaskDao taskDao ;
/** * 复杂查询测试 * @param page * @param size * @return */
public Page<Task> findBySepc(int page, int size){
PageRequest pageReq = this.buildPageRequest(page, size);
Page<Task> tasks = this.taskDao.findAll(new MySpec(), pageReq);
return tasks;
}
/** * 建立分页排序请求 * @param page * @param size * @return */
private PageRequest buildPageRequest(int page, int size) {
Sort sort = new Sort(Direction.DESC,"createTime");
return new PageRequest(page,size, sort);
}
/** * 建立查询条件 * @author liuxg * @date 2016年3月30日 下午2:04:39 */
private class MySpec implements Specification<Task>{
@Override
public Predicate toPredicate(Root<Task> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
//1.混合条件查询
/*Path<String> exp1 = root.get("taskName"); Path<Date> exp2 = root.get("createTime"); Path<String> exp3 = root.get("taskDetail"); Predicate predicate = cb.and(cb.like(exp1, "%taskName%"),cb.lessThan(exp2, new Date())); return cb.or(predicate,cb.equal(exp3, "kkk")); 类似的sql语句为: Hibernate: select count(task0_.id) as col_0_0_ from tb_task task0_ where ( task0_.task_name like ? ) and task0_.create_time<? or task0_.task_detail=? */
//2.多表查询
/*Join<Task,Project> join = root.join("project", JoinType.INNER); Path<String> exp4 = join.get("projectName"); return cb.like(exp4, "%projectName%"); Hibernate: select count(task0_.id) as col_0_0_ from tb_task task0_ inner join tb_project project1_ on task0_.project_id=project1_.id where project1_.project_name like ?*/
return null ;
}
}
}
3.实体类task代码如下
@Entity
@Table(name = "tb_task")
public class Task {
private Long id ;
private String taskName ;
private Date createTime ;
private Project project;
private String taskDetail ;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
@Column(name = "task_name")
public String getTaskName() {
return taskName;
}
public void setTaskName(String taskName) {
this.taskName = taskName;
}
@Column(name = "create_time")
@DateTimeFormat(pattern = "yyyy-MM-dd hh:mm:ss")
public Date getCreateTime() {
return createTime;
}
public void setCreateTime(Date createTime) {
this.createTime = createTime;
}
@Column(name = "task_detail")
public String getTaskDetail() {
return taskDetail;
}
public void setTaskDetail(String taskDetail) {
this.taskDetail = taskDetail;
}
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "project_id")
public Project getProject() {
return project;
}
public void setProject(Project project) {
this.project = project;
}
}
通过重写toPredicate方法,返回一个查询 Predicate,spring data jpa会帮我们进行查询。
也许你觉得,每次都要写一个类来实现Specification很麻烦,那或许你可以这么写
public class TaskSpec {
public static Specification<Task> method1(){
return new Specification<Task>(){
@Override
public Predicate toPredicate(Root<Task> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
return null;
}
};
}
public static Specification<Task> method2(){
return new Specification<Task>(){
@Override
public Predicate toPredicate(Root<Task> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
return null;
}
};
}
}
那么用的时候,我们就这么用
Page<Task> tasks = this.taskDao.findAll(TaskSpec.method1(), pageReq);
JpaSpecificationExecutor的介绍就到这里,下次再看看怎么通过写hql或者sql语句来进行查询