spring data jpa条件分组查询及分页

原book对象

 package com.shaying.domain;

 import javax.persistence.Column;
 import javax.persistence.Entity;
 import javax.persistence.GeneratedValue;
 import javax.persistence.GenerationType;
 import javax.persistence.Id;
 import javax.persistence.Table;

 import lombok.Data;

 @Data//可省略get、set方法，后续可直接使用get、set方法
 @Entity
 @Table(name="books")
 public class Book {
     @Id
     @GeneratedValue(strategy=GenerationType.IDENTITY)
     private Integer id;
     @Column()
     private String title;
     @Column()
     private Integer type;
     @Column()
     private double price;
     public Book(){}
     public Book(String title, double price) {
         this.title = title;
         this.price = price;
     }

     public String toString() {
         return "Book [id=" + id + ", title=" + title + ", type=" + type + ", price=" + price + "]";
     }
 }

BookInfo对象

 package com.shaying.domain;

 import lombok.Data;

 @Data
 public class BookInfo {
     private Integer type;
     private double maxPrice;
     private double sumPrice;

     public BookInfo(){}
     public BookInfo(Integer type, double maxPrice, double sumPrice) {
         this.type = type;
         this.maxPrice = maxPrice;
         this.sumPrice = sumPrice;
     }

     public String toString() {
         return "BookInfo [type=" + type + ", maxPrice=" + maxPrice + ", sumPrice=" + sumPrice + "]";
     }
 }

组建条件分组查询语句，返回分页查询结果

 package com.shaying.service;

 import java.util.List;

 import javax.persistence.EntityManager;
 import javax.persistence.TypedQuery;
 import javax.persistence.criteria.CriteriaBuilder;
 import javax.persistence.criteria.CriteriaQuery;
 import javax.persistence.criteria.Root;

 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.PageImpl;
 import org.springframework.data.domain.PageRequest;
 import org.springframework.data.domain.Pageable;
 import org.springframework.stereotype.Service;

 import com.shaying.domain.Book;
 import com.shaying.domain.BookInfo;

 @Service
 public class BookQueryService {

     @Autowired
     private EntityManager entityManager;

     /**
      * select type,max(price) maxPrice,sum(price) sumPrice from books group by type
      */
     public Page<BookInfo> groupBy(int index, int pageSize){
         //新建一个页面，存放页面信息
         Pageable page = new PageRequest(index, pageSize);
         //criteriaBuilder用于构建CriteriaQuery的构建器对象
         CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
         //criteriaQuery包含查询语句的各个部分，如where、max、sum、groupBy、orderBy等
         CriteriaQuery<BookInfo> criteriaQuery = criteriaBuilder.createQuery(BookInfo.class);
         //获取查询实例的属性，select * from books
         Root<Book> root = criteriaQuery.from(Book.class);
         //相当于select type,max(price) maxPrice,sum(price) sumPrice from books中select 与 from之间的部分
         criteriaQuery.multiselect(root.get("type"), criteriaBuilder.max(root.get("price")), criteriaBuilder.sum(root.get("price")));
         //where type = 1
         criteriaQuery.where(criteriaBuilder.equal(root.get("type"), 1));
         //group by type
         criteriaQuery.groupBy(root.get("type"));
         //criteriaQuery拼成的sql是select type,max(price) maxPrice,sum(price) sumPrice from books group by type；查询出的列与对象BookInfo的属性对应
         //记录当前sql查询结果总条数
         List<BookInfo> counts = entityManager.createQuery(criteriaQuery).getResultList();
         //sql查询对象
         TypedQuery<BookInfo> createQuery = entityManager.createQuery(criteriaQuery);
         //设置分页参数
         createQuery.setFirstResult(index*pageSize);
         createQuery.setMaxResults(pageSize);
         //返回查询的分页结果，createQuery.getResultList()为分页查询的结果对象，counts.size()为设置分页参数之前查询的总数
         return new PageImpl<BookInfo>(createQuery.getResultList(), page, counts.size());
     }
 }