SpringData JPA实现CRUD,分页与多参数排序

Posted 2020-10-17 若谷先生

　　Spring Data 项目的目的是为了简化构建基于 Spring 框架应用的数据访问计数，包括非关系数据库、Map-Reduce 框架、云数据服务等等，SpringData JPA是简化创建 JPA 数据访问层和跨存储的持久层功能，通过一个接口的继承即可实现简单的CRUD。

　　数据库的连接与项目的构建不说了，可以参考：springboot实战SpringDataJPA。我采用的是eclipse构建的普通的springboot项目。

一、创建表与实体类映射

@Entity
@Table(name = "student")
public class Student implements Serializable {
	@Id
	// id自动生成
	@GeneratedValue
	@Column(name = "id")
	private Long id;
	@Column(name = "name")
	private String name;
	@Column(name = "clas")
	private String clas;

	@Column(name = "interest")
	private String interest;

    // 省略了getter(),setter()方法　

二、创建StudentMapper 继承JpaRepository<Student, Long>，第一个参数是实体，第二个参数是主键的类型

public interface StudentMapper extends JpaRepository<Student, Long> {
	// int queryCount();
	// 自定义的方法实现findAll
	@Query(value = "select * from student where id < ?1", nativeQuery = true)
	public List<Student> findAll(Long id);
}

三、Controller内的代码如下：

@Resource
	private FirstPageService firstPageService;

	@RequestMapping(value = "/", method = RequestMethod.GET)
	@Fooish(tags = { "this_is_method" })
	String home() {
		return firstPageService.getString();
	}

	@RequestMapping(value = "/add", method = RequestMethod.GET)
	String addStudent(Student student) {
		return firstPageService.addStudent(student);
	}

	@RequestMapping(value = "/delete", method = RequestMethod.GET)
	String deleteStudent(Long id) {
		return firstPageService.deleteStudent(id);
	}

	@RequestMapping(value = "/update", method = RequestMethod.GET)
	String updateStudent(Student student) {
		return firstPageService.updateStudent(student);
	}

	@RequestMapping(value = "/list", method = RequestMethod.GET)
	List<Student> listStudent() {
		return firstPageService.listStudent();
	}

	// 采用的是自定义的方法
	@RequestMapping(value = "/list2", method = RequestMethod.GET)
	List<Student> list2Student(Long id) {
		return firstPageService.nativeQuery(id);
	}

	// 分页查询
	@RequestMapping(value = "/pageRequest", method = RequestMethod.GET)
	List<Student> pageRequest() {

		return firstPageService.pageRequest();
	}

	// 分页与排序查询
	@RequestMapping(value = "/pageAndSortRequest", method = RequestMethod.GET)
	List<Student> pageAndSortRequest() {

		return firstPageService.pageAndSortRequest();
	}

四、服务层firstPageService代码如下：

@Resource
	private StudentMapper studentMapper;

	public String getString() {

		// return name;
		// int a = studentMapper.queryCount();
		// return a + "";
		return "Hellow World!";
	}

	public String addStudent(Student stu) {
		studentMapper.save(stu);
		return "添加成功";
	}

	public String deleteStudent(Long id) {
		studentMapper.delete(id);
		return "删除成功";
	}

	public String updateStudent(Student stu) {
		// 如果有就更新，没有就添加
		studentMapper.save(stu);
		return "更新成功";
	}

	public List<Student> listStudent() {

		return studentMapper.findAll();
	}

	public List<Student> nativeQuery(Long id) {
		return studentMapper.findAll(id);
	}

　　　　// 分页查询
	public List<Student> pageRequest() {
		PageRequest pageRequest = new PageRequest(1, 3);
		Page<Student> stuPage = studentMapper.findAll(pageRequest);
		List<Student> stuList = stuPage.getContent();
		return stuList;
	}

　　　　// 分页与排序
	public List<Student> pageAndSortRequest() {
		Sort sort1 = new Sort(Sort.Direction.DESC, "id");
		Sort sort2 = new Sort(Sort.Direction.ASC, "name");
		// 把两个排序的条件取取与
		Sort sort = sort1.and(sort2);
		PageRequest pageRequest = new PageRequest(1, 2, sort);
		Page<Student> stuPage = studentMapper.findAll(pageRequest);
		List<Student> stuList = stuPage.getContent();
		return stuList;
	}

　　

通过源码的继承与实现关系可以看出，JpaRepository接口继承了PagingAndSortingRepository,QueryByExampleExecutor两个接口，PagingAndSortingRepository接口继承了CrudRepository。CrudRepository中包含了简单的数据库增，删，改，查，这四个操作还是比较简单的，下面主要介绍分页与排序；

下面的是PagingAndSortingRepository的源码：

public interface PagingAndSortingRepository extends CrudRepository {

	public abstract Iterable findAll(Sort sort);

	public abstract Page findAll(Pageable pageable);
}

这个接口提供了分页与排序的基本方法，想要实现分页查询，要实现Pageable接口，而PageRequest是该接口的一个实现类，该类的构造方法：

    // 单纯的分页
　　　　public PageRequest(int page, int size) {
		this(page, size, null);
	}

	public transient PageRequest(int page, int size, Sort.Direction direction,
			String properties[]) {
		this(page, size, new Sort(direction, properties));
	}
　　　　　　// 分页与排序，要实现Sort类
	public PageRequest(int page, int size, Sort sort) {
		super(page, size);
		this.sort = sort;
	}

　

五、按照id倒序，name顺序,查询第二页，每页显示两个的查询结果：