转载：spring boot-jpa整合QueryDSL来简化复杂操作

版权声明：本文为博主原创文章，转载请注明出处。 http://blog.csdn.net/liuchuanhong1/article/details/70244261

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

        <dependency>
            <groupId>com.querydslgroupId>
            <artifactId>querydsl-jpaartifactId>
        dependency>
        <dependency>
            <groupId>com.querydslgroupId>
            <artifactId>querydsl-aptartifactId>
            <scope>providedscope>
        dependency>

2、pom文件中，加入编译插件

<plugin>
                <groupId>com.mysema.mavengroupId>
                <artifactId>apt-maven-pluginartifactId>
                <version>1.1.3version>
                <executions>
                    <execution>
                        <goals>
                            <goal>processgoal>
                        goals>
                        <configuration>
                            <outputDirectory>target/generated-sources/javaoutputDirectory>
                            <processor>com.querydsl.apt.jpa.JPAAnnotationProcessorprocessor>
                        configuration>
                    execution>
                executions>
            plugin>

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(Pathextends User> 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

<outputDirectory>target/generated-sources/javaoutputDirectory>

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QueryDslPredicateExecutor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：

http://blog.csdn.net/liuchuanhong1/article/details/52042477

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：

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