如何定义这个原生查询返回类型？答案

【问题标题】：How to define this native query return type?如何定义这个原生查询返回类型？
【发布时间】：2020-12-19 15:50:46
【问题描述】：

为了计算添加到数据库表名称 url_store 的项目数，我使用 Spring JPA 的本机查询：

@Query(value="SELECT count(dateadded), dateadded from url_store WHERE dateadded >= ? and dateadded <= ? group by dateadded",
    nativeQuery=true)
    List<CountByDay> getAddedCountByDay(Date fromDate, Date toDate);

CountByDay DTO 对象，应该包含在返回的 List 中：

import java.util.Date;

public class CountByDay {

    public CountByDay(Integer count, Date dateAdded){
        this.count = count;
        this.dateAdded = dateAdded;
    }

    public Integer getCount() {
        return count;
    }

    public void setCount(Integer count) {
        this.count = count;
    }

    private Integer count;

    public Date getDateAdded() {
        return dateAdded;
    }

    public void setDateAdded(Date dateAdded) {
        this.dateAdded = dateAdded;
    }

    private Date dateAdded;

}

当我调用 getAddedCountByDay 方法时，我收到错误：

org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from type [org.springframework.data.jpa.repository.query.AbstractJpaQuery$TupleConverter$TupleBackedMap] to type [CountByDay]
    at org.springframework.core.convert.support.GenericConversionService.handleConverterNotFound(GenericConversionService.java:321) ~[spring-core-5.2.8.RELEASE.jar:5.2.8.RELEASE]

看来我没有正确定义 dto CountByDay？如何正确定义 dto 以返回 CountByDay 对象列表？

【问题讨论】：

标签： spring spring-boot jpa

【解决方案1】：

我建议你尝试使用构造函数表达式 JPQL：

SELECT new CountByDay(count(dateadded), dateadded) from url_store WHERE dateadded >= ? and dateadded <= ? group by dateadded

【讨论】：

【解决方案2】：

我得到了这个工作：

1.重新定义CountByDay

import java.util.Date;

public interface CountByDay {
Date getDateAdded();
int getCnt();
}

2.更新查询

@Query(value="SELECT count(dateadded) as cnt, dateadded as dateadded from url_store WHERE dateadded >= ? and dateadded <= ? group by dateadded",
    nativeQuery=true)
    List<CountByDay> getAddedCountByDay(Date fromDate, Date toDate);

这有帮助：No converter found capable of converting from type to type

【讨论】：