Spring数据JPA“找不到持久性实体”，用于列表[duplicate]

Question

很难弄清楚我是在打虫子还是在做傻事...

Spring Boot v2.0.0. M7，sping-data-jpa，sping-data-rest，MySQL

以下@Query

@Query("select DISTINCT item.statusCode from Item item")
public List<String> lookupStatusCodes();

在一个PagingAndSortingRepository上抛出一个

java.lang.IllegalArgumentException: Couldn't find PersistentEntity for type class java.lang.String!
at org.springframework.data.mapping.context.PersistentEntities.lambda$getRequiredPersistentEntity$2(PersistentEntities.java:78) ~[spring-data-commons-2.0.2.RELEASE.jar:2.0.2.RELEASE]
at java.util.Optional.orElseThrow(Unknown Source) ~[na:1.8.0_151]
at org.springframework.data.mapping.context.PersistentEntities.getRequiredPersistentEntity(PersistentEntities.java:77) ~[spring-data-commons-2.0.2.RELEASE.jar:2.0.2.RELEASE]
at org.springframework.data.rest.webmvc.PersistentEntityResourceAssembler.wrap(PersistentEntityResourceAssembler.java:72) ~[spring-data-rest-webmvc-3.0.2.RELEASE.jar:3.0.2.RELEASE]

statusCode是一个varchar，项本身作为@Entity按预期工作，但试图投影到字符串列表（或列表）

如果重要的话，我故意不想返回页面




Answer 1

无法直接映射字符串。你需要一个映射器对象。创建一个带有字符串字段的模型类-

package org.xyz.model;

import java.io.Serializable;

public class StringResult implements Serializable {

    private static final long serialVersionUID = 1L;
    private String result;

    public StringResult(
        String result) {
        super();
        this.result = result;
    }

    public String getResult() {
        return result;
    }
}

然后将查询更改为使用模型类-

@Query("select new org.xyz.model.StringResult(DISTINCT item.statusCode as result) from Item item")
public List<StringResult> lookupStatusCodes();