SPRING DATA REST PROJECTIONS，o.s.d.r.w.RepositoryRestExceptionHandler：PersistentEntity 不能为空

Question

应用程序属性：

spring.h2.console.enabled=true
spring.h2.console.path=/console
spring.datasource.url=jdbc:h2:mem:
logging.level.org.hibernate.SQL=debug`

这是我的 pom.xml：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>uk.co.rbrt</groupId>
    <artifactId>spring-data-native-query-projection</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>spring-data-native-query-projection</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.7.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-rest</artifactId>
        </dependency>

        <!-- Springs Java Persistence API -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <scope>runtime</scope>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>
</project>

数据类：

package uk.co.rbrt;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;


@Entity
public class Person
{
    @Id
    @GeneratedValue
    private Long id;

    @Column(nullable = false)
    private String name;

    @Column(nullable = false)
    private int age;

    public Person()
    {
        // default no-arg constructor
    }

    public Long getId()
    {
        return id;
    }

    public void setId(Long id)
    {
        this.id = id;
    }

    public String getName()
    {
        return name;
    }

    public void setName(String name)
    {
        this.name = name;
    }

    public int getAge()
    {
        return age;
    }

    public void setAge(int age)
    {
        this.age = age;
    }
}

投影界面：

package uk.co.rbrt;

public interface PersonSummary 
{
    String getName();

    int getAge();
}

存储库：

package uk.co.rbrt;

import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.CrudRepository;

import java.util.List;

public interface PersonRepository extends CrudRepository<Person, Long>
{
    List<PersonSummary> findAllProjectedBy();

    Query(value = "SELECT name AS name, age AS age FROM Person")
    List<PersonSummary> findAllProjectedJpaQuery();

    @Query(value = "SELECT name AS name, age AS age FROM Person", nativeQuery = true)
    List<PersonSummary> findAllProjectedNativeQuery();

    PersonSummary findProjectedById(long id);

    @Query(value = "SELECT name AS name, age AS age FROM Person WHERE id = ?1")
    PersonSummary findProjectedByIdJpaQuery(long id);

    @Query(value = "SELECT name AS name, age AS age FROM Person WHERE id = ?1", nativeQuery = true)
    PersonSummary findProjectedByIdNativeQuery(long id);
}

主类：

package uk.co.rbrt;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class SpringDataNativeQueryProjectionApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringDataNativeQueryProjectionApplication.class, args);
    }
}

但我得到了：

2017-09-17 18:15:11.242 DEBUG 8959 --- [nio-8080-exec-2] org.hibernate.SQL                        : SELECT name AS name, age AS age FROM Person
2017-09-17 18:15:11.246 ERROR 8959 --- [nio-8080-exec-2] o.s.d.r.w.RepositoryRestExceptionHandler : PersistentEntity must not be null!

使用 Eclipse Maven Springboot 项目，它编译正常，但我无法调试它，因为问题存在于框架中。

有人可以分享一下为什么春天会这样吗？它不应该识别投影接口并映射出 JSON 响应吗？

Answer 1

这里是带有 JPA 投影的更正 PersonRepository。

public interface PersonRepository extends CrudRepository<Person, Long>
{
    @Query(value = "SELECT p.name AS name, p.age AS age FROM Person AS p")
    List<PersonSummary> findAllProjectedJpaQuery();

    @Query(value = ""SELECT p.name AS name, p.age AS age FROM Person AS p"", nativeQuery = true)
    List<PersonSummary> findAllProjectedNativeQuery();

    PersonSummary findProjectedById(long id);

    @Query(value = "SELECT p.name AS name, p.age AS age FROM Person AS p WHERE id = ?1")
    PersonSummary findProjectedByIdJpaQuery(long id);

    @Query(value = "SELECT p.name AS name, p.age AS age FROM Person AS p", nativeQuery = true)
    PersonSummary findProjectedByIdNativeQuery(long id);

}

你可以找到一个具体的例子here。