使用jpa和querydsl来实现嵌套属性的查询

百科知识2025-04-261

1、引入相关的jpa和querydsl相关的包

com.querydsl querydsl-jpa ${querydsl.version} com.querydsl querydsl-apt ${querydsl.version} provided org.springframework.boot spring-boot-starter-data-jpa

说明:

  1. 我这里的jpa的版本没有配置版本号，是因为我的工程继承了一个parent的父工程，父工程已经配置了版本号，所以子工程会继承父工程的版本号，顺便说一下，这里我使用的版本号是2.5.5，因为我使用的spingboot的版本号是springboot2.5.5
  2. 同样的道理，我的父工程了配置了querydsl的版本，子工程直接继承，我这里的版本是4.4.0,但是这里有个疑问，我顺着父工程去寻找属性querydsl.version，但是没有找到，如果有小伙伴知道怎么找，希望能给我回复

2、引入实体类Message

@Entity
@Table(name = "msg_message")
public class Message implements Serializable {
@Id
@Column(name="id")
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
@Embedded
@AttributeOverrides({
@AttributeOverride( name = "address", column = @Column(name = "from_address")),
@AttributeOverride( name = "name", column = @Column(name = "from_name"))
})
private MessageAddress fromMessageAddress;
@AttributeOverrides({
@AttributeOverride( name = "address", column = @Column(name = "to_address")),
@AttributeOverride( name = "name", column = @Column(name = "to_name"))
})
@Embedded
private MessageAddress toMessageAddress;
private Long templateId;
private String sendMsg;
@Embedded
private Creator creator;
/**

  • 消息编码
    */
    private String messageCode;
    public String getMessageCode() {
    return messageCode;
    }
    private String status;
    public Message(){
    }
    private Message(MessageAddress fromMessageAddress, MessageAddress toMessageAddress, Long templateId,
    String sendMsg, Creator creator, String status) {
    this.fromMessageAddress = fromMessageAddress;
    this.toMessageAddress = toMessageAddress;
    this.templateId = templateId;
    this.sendMsg = sendMsg;
    this.creator = creator;
    this.status = status;
    this.messageCode = generateMessageCode();
    }
    private String generateMessageCode() {
    String msgCode="%s-%s-%s";
    //默认技术类，一般是站内信息
    String type = "1";
    Long templateId = this.templateId;
    Calendar calendar = Calendar.getInstance();
    int year = calendar.get(Calendar.YEAR);
    int month = calendar.get(Calendar.MONTH)+1;
    int date = calendar.get(Calendar.DAY_OF_MONTH);
    String time;
    if (month <10) {
    time = ""+year+"0"+month+date;
    } else {
    time = ""+year+month+date;
    }
    return String.format(msgCode, type,templateId, time);
    }
    public static Message newMessageInfo(MessageAddress fromMessageAddress, MessageAddress toMessageAddress, Long templateId,
    String sendMsg, Creator creator, String status) {
    return new Message(fromMessageAddress, toMessageAddress, templateId, sendMsg, creator,status);
    }
    public String getStatus() {
    return status;
    }
    public void setStatus(String status) {
    this.status = status;
    }
    public MessageAddress getFromMessageAddress() {
    return fromMessageAddress;
    }
    public void setFromMessageAddress(MessageAddress fromMessageAddress) {
    this.fromMessageAddress = fromMessageAddress;
    }
    public void setId(Long id) {
    this.id = id;
    }
    public MessageAddress getToMessageAddress() {
    return toMessageAddress;
    }
    public void setToMessageAddress(MessageAddress toMessageAddress) {
    this.toMessageAddress = toMessageAddress;
    }
    public Long getTemplateId() {
    return templateId;
    }
    public void setTemplateId(Long templateId) {
    this.templateId = templateId;
    }
    public String getSendMsg() {
    return sendMsg;
    }
    public void setSendMsg(String sendMsg) {
    this.sendMsg = sendMsg;
    }
    public Creator getCreator() {
    return creator;
    }
    public void setCreator(Creator creator) {
    this.creator = creator;
    }
    public void setMessageCode(String messageCode) {
    this.messageCode = messageCode;
    }
    @Override
    public String toString() {
    return "Message{" +
    "id=" + id +
    ", fromMessageAddress=" + fromMessageAddress +
    ", toMessageAddress=" + toMessageAddress +
    ", templateId=" + templateId +
    ", sendMsg='" + sendMsg + '\'' +
    ", creator=" + creator +
    ", messageCode='" + messageCode + '\'' +
    ", status='" + status + '\'' +
    '}';
    }
    }
    @Embeddable
    public class MessageAddress implements Serializable {
    private String address;
    private String name;
    public MessageAddress(){}
    public MessageAddress(String address, String name) {
    this.address = address;
    this.name = name;
    }
    public String getAddress() {
    return address;
    }
    public String getName() {
    return name;
    }
    @Override
    public String toString() {
    return "Address{" +
    "address='" + address + '\'' +
    ", name='" + name + '\'' +
    '}';
    }
    @Override
    public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;
    MessageAddress that = (MessageAddress) o;
    return address.equals(that.address);
    }
    @Override
    public int hashCode() {
    return Objects.hash(address);
    }
    }
    @Embeddable
    public class Creator {
    private Long creatorId;
    private String creatorName;
    private Long modifierId;
    private String telephone;
    private Long createTime;
    private Long modifyTime;
    public Creator(){}
    private Creator(Long creatorId, String creatorName, String telephone){
    this.creatorId = creatorId;
    this.creatorName = creatorName;
    this.telephone = telephone;
    this.createTime = System.currentTimeMillis();
    this.modifyTime = System.currentTimeMillis();
    this.modifierId = creatorId;
    }
    /**
  • 创建一个新的创建者信息
  • @param creatorId 创建人id
  • @param creatorName 创建人名称
  • @param telephone 电话号码
  • @return 创建者信息
    */
    public static Creator newCreatorInfo(Long creatorId, String creatorName, String telephone) {
    return new Creator(creatorId,creatorName,telephone);
    }
    public Creator withCreateTime(Long createTime) {
    this.createTime = createTime;
    return this;
    }
    public Creator withModifyTime() {
    this.modifyTime = System.currentTimeMillis();
    return this;
    }
    public Creator withModifierId(Long modifierId) {
    this.modifierId = modifierId;
    return this;
    }
    public Long getCreatorId() {
    return creatorId;
    }
    public String getCreatorName() {
    return creatorName;
    }
    public String getTelephone() {
    return telephone;
    }
    public Long getCreateTime() {
    return createTime;
    }
    public Long getModifyTime() {
    return modifyTime;
    }
    public void setCreatorId(Long creatorId) {
    this.creatorId = creatorId;
    }
    public void setCreatorName(String creatorName) {
    this.creatorName = creatorName;
    }
    public void setTelephone(String telephone) {
    this.telephone = telephone;
    }
    public void setCreateTime(Long createTime) {
    this.createTime = createTime;
    }
    public void setModifyTime(Long modifyTime) {
    this.modifyTime = modifyTime;
    }
    public Long getModifierId() {
    return modifierId;
    }
    @Override
    public String toString() {
    return "CreatorInfo{" +
    "creatorId=" + creatorId +
    ", creatorName='" + creatorName + '\'' +
    ", modifierId=" + modifierId +
    ", telephone='" + telephone + '\'' +
    ", createTime=" + createTime +
    ", modifyTime=" + modifyTime +
    '}';
    }
    }

    这里我需要对Message的属性toAddrsss里的字段address进行查询以及对sendMsg进行查询，还要按照creator属性里面的createTime进行排序，同时进行分页，

    由于我的这个对象具有嵌入的属性，所以在使用单纯的jsa进行分页查询的时候，我尝试了很多方法也没有成功，所以我才想尝试一下querydsl

    一下是我的query service方法

    /**

  • 能进行模糊匹配
  • @param address 消息接收者地址
  • @param page 页号
  • @param size 每页数据
  • @param sendMsg 消息内容查询参数
  • @return 分页消息信息
    */
    public Page queryMessageInfo(String address, int page, int size, String sendMsg) {
    Pageable pageable = PageRequest.of(page, size);
    QMessage message = QMessage.message;
    QueryResults queryResults = this.query.select(Projections.bean(MessageDto.class,
    message.sendMsg.as("msg"),message.id.as("id"),message.creator.createTime.as("createTime"))).from(message)
    .where(message.sendMsg.like(sendMsg).and(message.toMessageAddress.address.eq(address)))
    .orderBy(message.creator.createTime.desc())
    .offset(pageable.getOffset())
    .limit(pageable.getPageSize())
    .fetchResults();
    return new PageImpl<>(queryResults.getResults(),pageable, queryResults.getTotal());
    }

    一看到这里，小伙伴跟定会懵了，你的QMessage是哪里来的？你的MessageDto是做啥的呢？

    且听我慢慢说来

    1. 这个QMessage是插件生成的，因此需要在工程的pom中配置以下插件
    com.mysema.maven apt-maven-plugin 1.1.3 process target/generated-sources com.querydsl.apt.jpa.JPAAnnotationProcessor

          2.这个MessageDto就是为了只展示前台需要的数据，如果使用Message的话，会将全部数据返回给前台，这样也可以，但是不是最优化的做法。

          3.这里的this.query是啥？其实呢?它就是这个

    @Autowired
    private EntityManager entityManager;
    private JPAQuery query;
    @PostConstruct
    public void init() {
    this.query = new JPAQuery<>(entityManager);
    }
    注意:第一点中的代码会在maven build的时候才会生成，而且生成的目录是target/generated-sources
    如下图所示

注意：这里还特别用蓝色和黄色给予区别对待。
顺便贴出MessageDto对象
public class MessageDto {
private Long id;
private String msg;
private Long createTime;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getMsg() {
return msg;
}
public void setMsg(String msg) {
this.msg = msg;
}
public Long getCreateTime() {
return createTime;
}
public void setCreateTime(Long createTime) {
this.createTime = createTime;
}
}

最后我们在讨论下

QueryResults queryResults = this.query.select(message).from(message)
.where(message.sendMsg.like(sendMsg).and(message.toMessageAddress.address.eq(address)))
.orderBy(message.creator.createTime.desc())
.offset(pageable.getOffset())
.limit(pageable.getPageSize())
.fetchResults();

如果代码写成这样，会有什么好处和不好的地方？

如果不适用MessageDTo,只查询出Message的部分属性应该怎么写呢？

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文章标题：使用jpa和querydsl来实现嵌套属性的查询
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