如何映射弹簧数据jpa中的特定列？

Question

每当我点击提交按钮提供一些值，我想从数据库中选择一些列，并显示在我的jsp页面上。表单成功提交，但我得到这个错误：

java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to com.psc.Entity.CandidateappearagainstadvtcodeEntity

所以我觉得不管数据返回仓库不与Entity映射。请提出，如何解决这个问题？

控制器：

@RequestMapping(value = "/getCandidateDetails", method = RequestMethod.POST) 
    public String getCandidateDetails(Model model,@RequestParam("studentmasterid") String studentmasterid){ 
     System.out.println(studentmasterid); 
     List<CandidateappearagainstadvtcodeEntity> candidates=candidateappearagainstadvtcodeEntityRepository.findBystudentmasterid(studentmasterid); 

     return "payments"; 
    } 

模式是这样的：

@Entity 
@Table(name = "CANDIDATEAPPEARAGAINSTADVTCODE", schema = "PSCNEPALCOMMERCIALDATABASEU1", catalog = "") 
public class CandidateappearagainstadvtcodeEntity { 
    private long id; 
    private String advertisementcode; 
    private Integer ageonlastdateday; 
    private Integer ageonlastdatemonth; 
    private Integer ageonlastdateyear; 
    private String applicationnumber; 
    private String attendancestatus; 
    private String candidatefirstname; 
    private String dateofbirthinnepali; 
    private String documentverificationstatus; 
    private String examinationcenterid; 
    private String examresultsstatus; 
    private String fathername; 
    private Long firstcoding; 
    private String studentmasterid; 
    //getters setters// 

库：

public interface CandidateappearagainstadvtcodeEntityRepository extends JpaRepository<CandidateappearagainstadvtcodeEntity,Long> { 

    @Query("select c.studentmasterid,c.advertisementcode,c.candidatefirstname from CandidateappearagainstadvtcodeEntity c where c.studentmasterid=?1") 
    List<CandidateappearagainstadvtcodeEntity> findBystudentmasterid(String masterId); 
} 

的applicationContext.xml：

<?xml version="1.0" encoding="UTF-8"?> 
<beans xmlns="http://www.springframework.org/schema/beans" 
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
     xmlns:context="http://www.springframework.org/schema/context" 
     xmlns:util="http://www.springframework.org/schema/util" 
     xmlns:jpa="http://www.springframework.org/schema/data/jpa" 
     xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.2.xsd 
      http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsd 
      http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.2.xsd 
      http://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa-1.0.xsd"> 

    <context:annotation-config/> 
    <context:component-scan base-package="com.psc"/> 

    <bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"> 
    <property name="location"> 
    <value>/WEB-INF/db.properties</value> 
    </property> 
    </bean> 

    <!-- BoneCP configuration --> 
    <bean id="mainDataSource" class="com.jolbox.bonecp.BoneCPDataSource" destroy-method="close"> 
     <property name="driverClass" value="${jdbc.driver}" /> 
     <property name="jdbcUrl" value="${jdbc.url}" /> 
     <property name="username" value="${jdbc.username}"/> 
     <property name="password" value="${jdbc.password}"/> 
     <property name="idleConnectionTestPeriodInMinutes" value="60"/> 
     <property name="idleMaxAgeInMinutes" value="240"/> 
     <property name="maxConnectionsPerPartition" value="30"/> 
     <property name="minConnectionsPerPartition" value="10"/> 
     <property name="partitionCount" value="3"/> 
     <property name="acquireIncrement" value="5"/> 
     <property name="statementsCacheSize" value="100"/> 
     <property name="releaseHelperThreads" value="3"/> 
    </bean> 

    <!-- SPRING - JPA --> 
    <jpa:repositories 
      base-package="com.psc" /> 

    <bean class="org.springframework.orm.jpa.JpaTransactionManager" 
      id="transactionManager"> 
     <property name="entityManagerFactory" 
        ref="entityManagerFactory" /> 
     <property name="jpaDialect"> 
      <bean class="org.springframework.orm.jpa.vendor.HibernateJpaDialect" /> 
     </property> 
    </bean> 

    <bean id="entityManagerFactory" 
      class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"> 
     <property name="dataSource" ref="mainDataSource" /> 
     <property name="packagesToScan" value="com.psc"/> 
     <property name="jpaVendorAdapter"> 
      <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter"> 
       <property name="generateDdl" value="true" /> 
       <property name="showSql" value="false"/> 
       <property name="databasePlatform" value="org.hibernate.dialect.Oracle12cDialect"/> 
       <property name="database" value="ORACLE"/> 
      </bean> 
     </property> 
     <property name="jpaProperties"> 
      <props> 
       <prop key="hibernate.hbm2ddl.auto">update</prop> 
       <prop key="hibernate.dialect">org.hibernate.dialect.Oracle12cDialect</prop> 
      </props> 
     </property> 
    </bean> 

</beans> 

Answer 1

JPA存储库通常会返回域模型。从docs

Spring Data Repositories usually return the domain model when using query methods. However, sometimes, you may need to alter the view of that model for various reasons. In this section, you will learn how to define projections to serve up simplified and reduced views of resources.

你的库法findBystudentmasterid将返回一个列表Object[]因此ClassCastException。如果你想要得到特定的列试Projections。

Chekout docs和this回答如何使用投影。