Java 在JPA查询中有没有从数据库中选择特定列的方法_Java_Sql_Spring_Jpa_Spring Data Jpa

Java 在JPA查询中有没有从数据库中选择特定列的方法

java sql spring jpa

Java 在JPA查询中有没有从数据库中选择特定列的方法,java,sql,spring,jpa,spring-data-jpa,Java,Sql,Spring,Jpa,Spring Data Jpa,我试图执行一个JPA SQL查询，从数据库查询中选择特定的列：“select username，ranking_points_sum from user order by ranking_points_sum ASC” 我的用户实体： @Entity @Table public class User { @Id @GeneratedValue private int id; private String firstname; private String lastname

我试图执行一个JPA SQL查询，从数据库查询中选择特定的列：“select username，ranking_points_sum from user order by ranking_points_sum ASC”

我的用户实体：

@Entity
@Table
public class User {

  @Id
  @GeneratedValue
  private int id;

  private String firstname;
  private String lastname;
  private String username;
  private int rankingPointsSum;
  private String email;
  private String password;

  @ManyToMany
  private List<Role> roles;

  private String token;

  @ManyToOne
  private Team team;

  public int getId() {
    return id;
  }

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

  public String getFirstname() {
    return firstname;
  }

  public void setFirstname(String firstname) {
    this.firstname = firstname;
  }

  public String getLastname() {
    return lastname;
  }

  public void setLastname(String lastname) {
    this.lastname = lastname;
  }

  public String getUsername() {
    return username;
  }

  public void setUsername(String username) {
    this.username = username;
  }

  public int getRankingPointsSum() {
    return rankingPointsSum;
  }

  public void setRankingPointsSum(int rankingPointsSum) {
    this.rankingPointsSum = rankingPointsSum;
  }

  public String getEmail() {
    return email;
  }

  public void setEmail(String email) {
    this.email = email;
  }

  public String getPassword() {
    return password;
  }

  public void setPassword(String password) {
    this.password = password;
  }

  public Team getTeam() {
    return team;
  }

  public void setTeam(Team team) {
    this.team = team;
  }

  public List<Role> getRoles() {
    return roles;
  }

  public void setRoles(List<Role> roles) {
    this.roles = roles;
  }

  public String getToken() {
    return token;
  }

  public void setToken(String token) {
    this.token = token;
  }
}

当我将其作为Spring启动应用程序运行并调用时，我得到以下错误：

Sun Mar 31 14:21:33 CEST 2019
There was an unexpected error (type=Internal Server Error, status=500).
could not execute query; SQL [SELECT username, ranking_points_sum from user order by ranking_points_sum ASC]; nested exception is org.hibernate.exception.SQLGrammarException: could not execute query
org.springframework.dao.InvalidDataAccessResourceUsageException: could not execute query; SQL [SELECT username, ranking_points_sum from user order by ranking_points_sum ASC]; nested exception is org.hibernate.exception.SQLGrammarException: could not execute query
    at org.springframework.orm.jpa.vendor.HibernateJpaDialect.convertHibernateAccessException(HibernateJpaDialect.java:279)
    at org.springframework.orm.jpa.vendor.HibernateJpaDialect.translateExceptionIfPossible(HibernateJpaDialect.java:253)
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.translateExceptionIfPossible(AbstractEntityManagerFactoryBean.java:527)
    at org.springframework.dao.support.ChainedPersistenceExceptionTranslator.translateExceptionIfPossible(ChainedPersistenceExceptionTranslator.java:61)
    at org.springframework.dao.support.DataAccessUtils.translateIfNecessary(DataAccessUtils.java:242)
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:153)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
    at org.springframework.data.jpa.repository.support.CrudMethodMetadataPostProcessor$CrudMethodMetadataPopulatingMethodInterceptor.invoke(CrudMethodMetadataPostProcessor.java:135)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:93)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
    at org.springframework.data.repository.core.support.SurroundingTransactionDetectorMethodInterceptor.invoke(SurroundingTransactionDetectorMethodInterceptor.java:61)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:212)
    at com.sun.proxy.$Proxy101.getRankingList(Unknown Source)
    at hhn.labsw.bugageocaching.controller.Controller.getRankingList(Controller.java:309)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:189)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:800)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1038)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1005)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:897)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:882)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:92)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:200)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:834)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1415)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:748)
Caused by: org.hibernate.exception.SQLGrammarException: could not execute query
    at org.hibernate.exception.internal.SQLExceptionTypeDelegate.convert(SQLExceptionTypeDelegate.java:63)
    at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:42)
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:113)
    at org.hibernate.loader.Loader.doList(Loader.java:2692)
    at org.hibernate.loader.Loader.doList(Loader.java:2672)
    at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2506)
    at org.hibernate.loader.Loader.list(Loader.java:2501)
    at org.hibernate.loader.custom.CustomLoader.list(CustomLoader.java:338)
    at org.hibernate.internal.SessionImpl.listCustomQuery(SessionImpl.java:2223)
    at org.hibernate.internal.AbstractSharedSessionContract.list(AbstractSharedSessionContract.java:1053)
    at org.hibernate.query.internal.NativeQueryImpl.doList(NativeQueryImpl.java:170)
    at org.hibernate.query.internal.AbstractProducedQuery.list(AbstractProducedQuery.java:1505)
    at org.hibernate.query.Query.getResultList(Query.java:135)
    at org.springframework.data.jpa.repository.query.JpaQueryExecution$CollectionExecution.doExecute(JpaQueryExecution.java:129)
    at org.springframework.data.jpa.repository.query.JpaQueryExecution.execute(JpaQueryExecution.java:91)
    at org.springframework.data.jpa.repository.query.AbstractJpaQuery.doExecute(AbstractJpaQuery.java:136)
    at org.springframework.data.jpa.repository.query.AbstractJpaQuery.execute(AbstractJpaQuery.java:125)
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.doInvoke(RepositoryFactorySupport.java:605)
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.lambda$invoke$3(RepositoryFactorySupport.java:595)
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.invoke(RepositoryFactorySupport.java:595)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
    at org.springframework.data.projection.DefaultMethodInvokingMethodInterceptor.invoke(DefaultMethodInvokingMethodInterceptor.java:59)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:294)
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:98)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:139)
    ... 64 more
Caused by: java.sql.SQLSyntaxErrorException: No such column: id
    at org.mariadb.jdbc.internal.util.exceptions.ExceptionMapper.get(ExceptionMapper.java:236)
    at org.mariadb.jdbc.internal.com.read.dao.ColumnNameMap.getIndex(ColumnNameMap.java:133)
    at org.mariadb.jdbc.internal.com.read.resultset.SelectResultSet.findColumn(SelectResultSet.java:1484)
    at org.mariadb.jdbc.internal.com.read.resultset.SelectResultSet.getInt(SelectResultSet.java:1062)
    at com.zaxxer.hikari.pool.HikariProxyResultSet.getInt(HikariProxyResultSet.java)
    at org.hibernate.type.descriptor.sql.IntegerTypeDescriptor$2.doExtract(IntegerTypeDescriptor.java:62)
    at org.hibernate.type.descriptor.sql.BasicExtractor.extract(BasicExtractor.java:47)
    at org.hibernate.type.AbstractStandardBasicType.nullSafeGet(AbstractStandardBasicType.java:261)
    at org.hibernate.type.AbstractStandardBasicType.nullSafeGet(AbstractStandardBasicType.java:257)
    at org.hibernate.type.AbstractStandardBasicType.nullSafeGet(AbstractStandardBasicType.java:247)
    at org.hibernate.type.AbstractStandardBasicType.hydrate(AbstractStandardBasicType.java:333)
    at org.hibernate.loader.Loader.extractKeysFromResultSet(Loader.java:793)
    at org.hibernate.loader.Loader.getRowFromResultSet(Loader.java:718)
    at org.hibernate.loader.Loader.processResultSet(Loader.java:990)
    at org.hibernate.loader.Loader.doQuery(Loader.java:948)
    at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:340)
    at org.hibernate.loader.Loader.doList(Loader.java:2689)
    ... 87 more

如果我将JPA Repository查询更改为从数据库中选择所有内容，如下所示：

public interface UserRepository extends CrudRepository<User, Integer> {
  User findByUsername(String username);

  @Query(value = "SELECT * from user order by ranking_points_sum ASC", nativeQuery = true)
  List<User> getRankingList();
}

问题是，我不需要整个数据库表，我只需要这两列用户名，作为JSON返回的排名点和

那么，有什么方法可以做到这一点吗？

异常消息说没有这样的列：id。这意味着，从数据库中获取的任何内容都没有实体映射所需的字段

换句话说，您不能执行以下操作：

"SELECT username, ranking_points_sum from user order by ranking_points_sum ASC"

比如说，结果是一个用户列表，因为用户实体有字段，这些字段需要是查询的结果，比如id。这也是为什么使用*的同一个查询可以工作的原因——所有列都是获取的，所有字段都是映射的。

JPA SQL query:没有这样的事情。要么是SQL，要么是JPQL，这是不同的语言。查询选择两列，但方法的返回类型为List。用户有更多的属性，这些属性不是由查询返回的。因此，不能仅从两个返回列创建用户。如果您希望查询返回一个用户，只需使用带有select u from User u….的JPQL查询。。。。如果您需要两个属性，那么也可以使用JPQL，选择u.username，u.rankingPointsSum from User u…，但将返回类型设置为List。@JBNizet那么我如何才能将这两个属性作为JSON返回，而不构造用户对象？请参阅我编辑的注释。但是，从数据库控制台执行查询时，它不会出现任何问题。

public interface UserRepository extends CrudRepository<User, Integer> {
  User findByUsername(String username);

  @Query(value = "SELECT * from user order by ranking_points_sum ASC", nativeQuery = true)
  List<User> getRankingList();
}

// 20190331142532
// http://localhost:8080/api/getRankingList

[
  {
    "id": 1,
    "firstname": "Timo",
    "lastname": "Volkmann",
    "username": "moximoti",
    "rankingPointsSum": 0,
    "email": "test@user.com",
    "password": "$2a$10$c3Fo5nuUG.nlwXP94qc7qO01/UC1OL2DebEm.5zYlisKJGRhXMnqq",
    "roles": [
      {
        "id": 0,
        "name": "admin"
      }
    ],
    "token": "$2a$10$3hIZTTN/96h8LU0tEF/em.mhTZr8e14oug94JjOknRtDMMHZc/doK"
  }
]

"SELECT username, ranking_points_sum from user order by ranking_points_sum ASC"