详解spring boot jpa整合QueryDSL来简化复杂操作

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：//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

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持脚本之家。