小编给大家分享一下spring boot jpa如何整合QueryDSL来简化复杂操作，相信大部分人都还不怎么了解，因此分享这篇文章给大家参考一下，希望大家阅读完这篇文章后大有收获，下面让我们一起去了解一下吧！
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前言
使用过spring data jpa的同学，都很清楚，对于复杂的sql查询，处理起来还是比较复杂的，而本文中的QueryDSL就是用来简化JPA操作的。
Querydsl定义了一种常用的静态类型语法，用于在持久域模型数据之上进行查询。JDO和JPA是Querydsl的主要集成技术。本文旨在介绍如何使用Querydsl与JPA组合使用。JPA的Querydsl是JPQL和Criteria查询的替代方法。QueryDSL仅仅是一个通用的查询框架，专注于通过Java API构建类型安全的SQL查询。
要想使用QueryDSL，需要做两个前提操作：
1、pom文件中，加入依赖
com.querydsl
querydsl-jpa
com.querydsl
querydsl-apt
provided
2、pom文件中，加入编译插件
com.mysema.maven
apt-maven-plugin
1.1.3
process
target/generated-sources/java
com.querydsl.apt.jpa.JPAAnnotationProcessor
该插件会查找使用javax.persistence.Entity注解的域类型，并为它们生成对应的查询类型。下面以User实体类来说明，生成的查询类型如下：
package com.chhliu.springboot.jpa.entity;
import static com.querydsl.core.types.PathMetadataFactory.*;
import com.querydsl.core.types.dsl.*;
import com.querydsl.core.types.PathMetadata;
import javax.annotation.Generated;
import com.querydsl.core.types.Path;
/**
* QUser is a Querydsl query type for User
*/
@Generated("com.querydsl.codegen.EntitySerializer")
public class QUser extends EntityPathBase {
private static final long serialVersionUID = 1153899872L;
public static final QUser user = new QUser("user");
public final StringPath address = createString("address");
public final NumberPath age = createNumber("age", Integer.class);
public final NumberPath id = createNumber("id", Integer.class);
public final StringPath name = createString("name");
public QUser(String variable) {
super(User.class, forVariable(variable));
}
public QUser(Path path) {
super(path.getType(), path.getMetadata());
}
public QUser(PathMetadata metadata) {
super(User.class, metadata);
}
}我们建立好实体类之后，然后运行mvn clean complie命令，就会在
target/generated-sources/java
目录下生成对应的查询类型。然后将生成的类都拷贝到项目中，即可。
本文涉及到的Entity如下：
package com.chhliu.springboot.jpa.entity;
import java.io.Serializable;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
@Entity
@Table(name="t_user")
public class User implements Serializable{
/**
*
*/
private static final long serialVersionUID = 1L;
@Id()
@GeneratedValue(strategy = GenerationType.AUTO)
private int id;
private String name;
private String address;
private int age;
…………省略getter，setter方法…………
/**
* attention:
* Details：方便查看测试结果
* @author chhliu
*/
@Override
public String toString() {
return "User [id=" + id + ", name=" + name + ", address=" + address + ", age=" + age + "]";
}
}上面的这个实体类，主要用于单表操作。
package com.chhliu.springboot.jpa.entity;
import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToOne;
import javax.persistence.Table;
/**
* 描述：TODO
* @author chhliu
*/
@Entity
@Table(name="PERSON")
public class Person {
@Id
@GeneratedValue
private Integer id;
private String name;
private String address;
@OneToOne(mappedBy="person", cascade={CascadeType.PERSIST, CascadeType.REMOVE, CascadeType.MERGE})
private IDCard idCard;
…………省略getter，setter方法…………
@Override
public String toString() {
return "Person [id=" + id + ", name=" + name + ", address=" + address + ", idCard=" + idCard + "]";
}
}package com.chhliu.springboot.jpa.entity;
import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToOne;
import javax.persistence.Table;
/**
* 描述：
* @author chhliu
*/
@Entity
@Table(name="IDCARD")
public class IDCard {
@Id
@GeneratedValue
private Integer id;
private String idNo;
@OneToOne(cascade={CascadeType.MERGE, CascadeType.REMOVE, CascadeType.PERSIST}, fetch=FetchType.EAGER)
private Person person;
…………省略getter，setter方法…………
@Override
public String toString() {
return "IDCard [id=" + id + ", idNo=" + idNo + ", person=" + person + "]";
}
}上面两个Entity主要用于一对一关系的示例操作
package com.chhliu.springboot.jpa.entity;
import java.util.List;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
/**
* 描述：Order实体类
* @author chhliu
*/
@Entity
@Table(name="ORDER_C")
public class Order {
@Id
@GeneratedValue
@Column(name="ID")
private Integer id;
@Column(length=20, name="ORDER_NAME")
private String orderName;
@Column(name="COUNT")
private Integer count;
@OneToMany(mappedBy = "order",cascade={CascadeType.PERSIST,CascadeType.REMOVE},fetch = FetchType.EAGER)
private List orderItems;
…………省略getter，setter方法…………
}package com.chhliu.springboot.jpa.entity;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;
/**
* 描述：OrderItem实体类
* @author chhliu
*/
@Entity
@Table(name="ORDER_ITEM")
public class OrderItem {
@Id
@GeneratedValue
@Column(name="ID", nullable=false)
private Integer id;
@Column(name="ITEM_NAME", length=20)
private String itemName;
@Column(name="PRICE")
private Integer price;
@ManyToOne(cascade={CascadeType.PERSIST,CascadeType.REMOVE, CascadeType.MERGE}, fetch=FetchType.EAGER)
@JoinColumn(name = "ORDER_ID")
private Order order;
…………省略getter，setter方法…………
}上面两个Entity用于展示一对多关系的示例操作。
首先，我们来看单表操作
1、使用spring data jpa
要想使用spring data jpa提供的QueryDSL功能，很简单，直接继承接口即可。Spring Data JPA中提供了QueryDslPredicateExecutor接口,用于支持QueryDSL的查询操作接口，如下：
package com.chhliu.springboot.jpa.repository;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.querydsl.QueryDslPredicateExecutor;
import com.chhliu.springboot.jpa.entity.User;
public interface UserRepositoryDls extends JpaRepository, QueryDslPredicateExecutor{
// 继承接口
}
QueryDslPredicateExecutor接口提供了如下方法：
public interface QueryDslPredicateExecutor {
T findOne(Predicate predicate);
Iterable findAll(Predicate predicate);
Iterable findAll(Predicate predicate, Sort sort);
Iterable findAll(Predicate predicate, OrderSpecifier... orders);
Iterable findAll(OrderSpecifier... orders);
Page findAll(Predicate predicate, Pageable pageable);
long count(Predicate predicate);
boolean exists(Predicate predicate);
}
以上方法的使用和spring data jpa中的其他接口使用方法类似，详情请参考：https://www.jb51.net/article/137757.htm
测试如下：
public User findUserByUserName(final String userName){
/**
* 该例是使用spring data QueryDSL实现
*/
QUser quser = QUser.user;
Predicate predicate = quser.name.eq(userName);// 根据用户名，查询user表
return repository.findOne(predicate);
}对应的sql如下：
复制代码 代码如下:
select user0_.id as id1_5_, user0_.address as address2_5_, user0_.age as age3_5_, user0_.name as name4_5_ from t_user user0_ where user0_.name=?
单表操作示例代码如下：
package com.chhliu.springboot.jpa.repository;
import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.Query;
import javax.transaction.Transactional;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageRequest;
import org.springframework.data.domain.Sort;
import org.springframework.stereotype.Component;
import com.chhliu.springboot.jpa.entity.QUser;
import com.chhliu.springboot.jpa.entity.User;
import com.querydsl.core.types.Predicate;
import com.querydsl.jpa.impl.JPAQueryFactory;
/**
* 描述：QueryDSL JPA
* @author chhliu
*/
@Component
@Transactional
public class UserRepositoryManagerDsl {
@Autowired
private UserRepositoryDls repository;
@Autowired
@PersistenceContext
private EntityManager entityManager;
private JPAQueryFactory queryFactory;
@PostConstruct
public void init() {
queryFactory = new JPAQueryFactory(entityManager);
}
public User findUserByUserName(final String userName){
/**
* 该例是使用spring data QueryDSL实现
*/
QUser quser = QUser.user;
Predicate predicate = quser.name.eq(userName);
return repository.findOne(predicate);
}
/**
* attention:
* Details：查询user表中的所有记录
*/
public List findAll(){
QUser quser = QUser.user;
return queryFactory.selectFrom(quser)
.fetch();
}
/**
* Details：单条件查询
*/
public User findOneByUserName(final String userName){
QUser quser = QUser.user;
return queryFactory.selectFrom(quser)
.where(quser.name.eq(userName))
.fetchOne();
}
/**
* Details：单表多条件查询
*/
public User findOneByUserNameAndAddress(final String userName, final String address){
QUser quser = QUser.user;
return queryFactory.select(quser)
.from(quser) // 上面两句代码等价与selectFrom
.where(quser.name.eq(userName).and(quser.address.eq(address)))// 这句代码等同于where(quser.name.eq(userName), quser.address.eq(address))
.fetchOne();
}
/**
* Details：使用join查询
*/
public List findUsersByJoin(){
QUser quser = QUser.user;
QUser userName = new QUser("name");
return queryFactory.selectFrom(quser)
.innerJoin(quser)
.on(quser.id.intValue().eq(userName.id.intValue()))
.fetch();
}
/**
* Details：将查询结果排序
*/
public List findUserAndOrder(){
QUser quser = QUser.user;
return queryFactory.selectFrom(quser)
.orderBy(quser.id.desc())
.fetch();
}
/**
* Details：Group By使用
*/
public List findUserByGroup(){
QUser quser = QUser.user;
return queryFactory.select(quser.name)
.from(quser)
.groupBy(quser.name)
.fetch();
}
/**
* Details：删除用户
*/
public long deleteUser(String userName){
QUser quser = QUser.user;
return queryFactory.delete(quser).where(quser.name.eq(userName)).execute();
}
/**
* Details：更新记录
*/
public long updateUser(final User u, final String userName){
QUser quser = QUser.user;
return queryFactory.update(quser).where(quser.name.eq(userName))
.set(quser.name, u.getName())
.set(quser.age, u.getAge())
.set(quser.address, u.getAddress())
.execute();
}
/**
* Details：使用原生Query
*/
public User findOneUserByOriginalSql(final String userName){
QUser quser = QUser.user;
Query query = queryFactory.selectFrom(quser)
.where(quser.name.eq(userName)).createQuery();
return (User) query.getSingleResult();
}
/**
* Details：分页查询单表
*/
public Page findAllAndPager(final int offset, final int pageSize){
Predicate predicate = QUser.user.id.lt(10);
Sort sort = new Sort(new Sort.Order(Sort.Direction.DESC, "id"));
PageRequest pr = new PageRequest(offset, pageSize, sort);
return repository.findAll(predicate, pr);
}
}多表操作示例(一对一)如下：
package com.chhliu.springboot.jpa.repository;
import java.util.ArrayList;
import java.util.List;
import javax.annotation.PostConstruct;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import com.chhliu.springboot.jpa.dto.PersonIDCardDto;
import com.chhliu.springboot.jpa.entity.QIDCard;
import com.chhliu.springboot.jpa.entity.QPerson;
import com.querydsl.core.QueryResults;
import com.querydsl.core.Tuple;
import com.querydsl.core.types.Predicate;
import com.querydsl.jpa.impl.JPAQuery;
import com.querydsl.jpa.impl.JPAQueryFactory;
@Component
public class PersonAndIDCardManager {
@Autowired
@PersistenceContext
private EntityManager entityManager;
private JPAQueryFactory queryFactory;
@PostConstruct
public void init() {
queryFactory = new JPAQueryFactory(entityManager);
}
/**
* Details：多表动态查询
*/
public List findAllPersonAndIdCard(){
Predicate predicate = (QPerson.person.id.intValue()).eq(QIDCard.iDCard.person.id.intValue());
JPAQuery jpaQuery = queryFactory.select(QIDCard.iDCard.idNo, QPerson.person.address, QPerson.person.name)
.from(QIDCard.iDCard, QPerson.person)
.where(predicate);
return jpaQuery.fetch();
}
/**
* Details：将查询结果以DTO的方式输出
*/
public List findByDTO(){
Predicate predicate = (QPerson.person.id.intValue()).eq(QIDCard.iDCard.person.id.intValue());
JPAQuery jpaQuery = queryFactory.select(QIDCard.iDCard.idNo, QPerson.person.address, QPerson.person.name)
.from(QIDCard.iDCard, QPerson.person)
.where(predicate);
List tuples = jpaQuery.fetch();
List dtos = new ArrayList();
if(null != tuples && !tuples.isEmpty()){
for(Tuple tuple:tuples){
String address = tuple.get(QPerson.person.address);
String name = tuple.get(QPerson.person.name);
String idCard = tuple.get(QIDCard.iDCard.idNo);
PersonIDCardDto dto = new PersonIDCardDto();
dto.setAddress(address);
dto.setIdNo(idCard);
dto.setName(name);
dtos.add(dto);
}
}
return dtos;
}
/**
* Details：多表动态查询，并分页
*/
public QueryResults findByDtoAndPager(int offset, int pageSize){
Predicate predicate = (QPerson.person.id.intValue()).eq(QIDCard.iDCard.person.id.intValue());
return queryFactory.select(QIDCard.iDCard.idNo, QPerson.person.address, QPerson.person.name)
.from(QIDCard.iDCard, QPerson.person)
.where(predicate)
.offset(offset)
.limit(pageSize)
.fetchResults();
}
}上面将查询结果以DTO的方式输出的示例中，在查询结束后，将查询结果手动的转换成了DTO对象，这种方式其实不太优雅，QueryDSL给我们提供了更好的方式，见下面的示例：
/**
* Details：方式一：使用Bean投影
*/
public List findByDTOUseBean(){
Predicate predicate = (QPerson.person.id.intValue()).eq(QIDCard.iDCard.person.id.intValue());
return queryFactory.select(
Projections.bean(PersonIDCardDto.class, QIDCard.iDCard.idNo, QPerson.person.address, QPerson.person.name))
.from(QIDCard.iDCard, QPerson.person)
.where(predicate)
.fetch();
}
/**
* Details：方式二：使用fields来代替setter
*/
public List findByDTOUseFields(){
Predicate predicate = (QPerson.person.id.intValue()).eq(QIDCard.iDCard.person.id.intValue());
return queryFactory.select(
Projections.fields(PersonIDCardDto.class, QIDCard.iDCard.idNo, QPerson.person.address, QPerson.person.name))
.from(QIDCard.iDCard, QPerson.person)
.where(predicate)
.fetch();
}
/**
* Details：方式三：使用构造方法，注意构造方法中属性的顺序必须和构造器中的顺序一致
*/
public List findByDTOUseConstructor(){
Predicate predicate = (QPerson.person.id.intValue()).eq(QIDCard.iDCard.person.id.intValue());
return queryFactory.select(
Projections.constructor(PersonIDCardDto.class, QPerson.person.name, QPerson.person.address, QIDCard.iDCard.idNo))
.from(QIDCard.iDCard, QPerson.person)
.where(predicate)
.fetch();
}
上面只是提供了几种思路，当然，还可以使用@QueryProjection来实现，非常灵活。
一对多示例：
package com.chhliu.springboot.jpa.repository;
import java.util.List;
import javax.annotation.PostConstruct;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import com.chhliu.springboot.jpa.entity.QOrder;
import com.chhliu.springboot.jpa.entity.QOrderItem;
import com.querydsl.core.Tuple;
import com.querydsl.core.types.Predicate;
import com.querydsl.jpa.impl.JPAQuery;
import com.querydsl.jpa.impl.JPAQueryFactory;
@Component
public class OrderAndOrderItemManager {
@Autowired
@PersistenceContext
private EntityManager entityManager;
private JPAQueryFactory queryFactory;
@PostConstruct
public void init() {
queryFactory = new JPAQueryFactory(entityManager);
}
/**
* Details：一对多，条件查询
*/
public List findOrderAndOrderItemByOrderName(String orderName){
//添加查询条件
Predicate predicate = QOrder.order.orderName.eq(orderName);
JPAQuery jpaQuery = queryFactory.select(QOrder.order, QOrderItem.orderItem)
.from(QOrder.order, QOrderItem.orderItem)
.where(QOrderItem.orderItem.order.id.intValue().eq(QOrder.order.id.intValue()), predicate);
//拿到结果
return jpaQuery.fetch();
}
/**
* Details：多表连接查询
*/
public List findAllByOrderName(String orderName){
//添加查询条件
Predicate predicate = QOrder.order.orderName.eq(orderName);
JPAQuery jpaQuery = queryFactory.select(QOrder.order, QOrderItem.orderItem)
.from(QOrder.order, QOrderItem.orderItem)
.rightJoin(QOrder.order)
.on(QOrderItem.orderItem.order.id.intValue().eq(QOrder.order.id.intValue()));
jpaQuery.where(predicate);
//拿到结果
return jpaQuery.fetch();
}
}从上面的示例中，我们可以看出，QueryDSL大大的简化了我们的操作
以上是“spring boot jpa如何整合QueryDSL来简化复杂操作”这篇文章的所有内容，感谢各位的阅读！相信大家都有了一定的了解，希望分享的内容对大家有所帮助，如果还想学习更多知识，欢迎关注创新互联行业资讯频道！
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