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

<!--query dsl --> <dependency> <groupId>com.querydsl</groupId> <artifactId>querydsl-jpa</artifactId> </dependency> <dependency> <groupId>com.querydsl</groupId> <artifactId>querydsl-apt</artifactId> <scope>provided</scope> </dependency>

2、pom文件中，加入编译插件

<plugin> <groupId>com.mysema.maven</groupId> <artifactId>apt-maven-plugin</artifactId> <version>1.1.3</version> <executions> <execution> <goals> <goal>process</goal> </goals> <configuration> <outputDirectory>target/generated-sources/java</outputDirectory> <processor>com.querydsl.apt.jpa.JPAAnnotationProcessor</processor> </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<User> { private static final long serialVersionUID = 1153899872L; public static final QUser user = new QUser("user"); public final StringPath address = createString("address"); public final NumberPath<Integer> age = createNumber("age", Integer.class); public final NumberPath<Integer> id = createNumber("id", Integer.class); public final StringPath name = createString("name"); public QUser(String variable) { super(User.class, forVariable(variable)); } public QUser(Path<? extends 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/java</outputDirectory>

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<OrderItem> 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<User, Integer>, QueryDslPredicateExecutor<User>{// 继承接口 }

QueryDslPredicateExecutor接口提供了如下方法：

public interface QueryDslPredicateExecutor<T> { T findOne(Predicate predicate); Iterable<T> findAll(Predicate predicate); Iterable<T> findAll(Predicate predicate, Sort sort); Iterable<T> findAll(Predicate predicate, OrderSpecifier<?>... orders); Iterable<T> findAll(OrderSpecifier<?>... orders); Page<T> 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：

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<User> 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<User> 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<User> findUserAndOrder(){ QUser quser = QUser.user; return queryFactory.selectFrom(quser) .orderBy(quser.id.desc()) .fetch(); } /** * Details：Group By使用 */ public List<String> 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<User> 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<Tuple> findAllPersonAndIdCard(){ Predicate predicate = (QPerson.person.id.intValue()).eq(QIDCard.iDCard.person.id.intValue()); JPAQuery<Tuple> 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<PersonIDCardDto> findByDTO(){ Predicate predicate = (QPerson.person.id.intValue()).eq(QIDCard.iDCard.person.id.intValue()); JPAQuery<Tuple> jpaQuery = queryFactory.select(QIDCard.iDCard.idNo, QPerson.person.address, QPerson.person.name) .from(QIDCard.iDCard, QPerson.person) .where(predicate); List<Tuple> tuples = jpaQuery.fetch(); List<PersonIDCardDto> dtos = new ArrayList<PersonIDCardDto>(); 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<Tuple> 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<PersonIDCardDto> 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<PersonIDCardDto> 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<PersonIDCardDto> 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<Tuple> findOrderAndOrderItemByOrderName(String orderName){ //添加查询条件 Predicate predicate = QOrder.order.orderName.eq(orderName); JPAQuery<Tuple> 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<Tuple> findAllByOrderName(String orderName){ //添加查询条件 Predicate predicate = QOrder.order.orderName.eq(orderName); JPAQuery<Tuple> 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。