“.”处或附近的QueryDSL语法错误在多对多的关系

Posted 2023-03-16

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【中文标题】“.”处或附近的QueryDSL语法错误在多对多的关系【英文标题】：QueryDSL syntax error at or near "." at many to many relationship 【发布时间】：2020-12-28 09:45:39 【问题描述】：

我正在尝试通过提供用户名从 PostgreSQL 数据库中检索用户密码和他的相关角色，没有什么太复杂的，但是，当我尝试检索我得到的这些数据时，我从 queryDSL 中得到了一些奇怪的行为SQL 语法错误：“.”处或附近的语法错误

我已经在这个项目中将 queryDSL 用于更复杂的查询，并且效果很好。

这里我使用的是投影方法，但是我也尝试使用 Tuple 而不创建投影类，并且错误完全相同。

投影：

@QueryEntity
@Immutable
public class UserAuth 

    private String password;
    private Set<Role> roles;

    public UserAuth(String password, Set<Role> roles) 
        this.password = password;
        this.roles = roles;
    

    getters and setters

以及它自己的查询：

String username = "Tom";
QUser user = QUser.user;
JPAQueryFactory queryFactory = new JPAQueryFactory(entityManager);
        UserAuth userAuth = queryFactory
                .select(Projections.constructor(UserAuth.class, user.password, user.roles))
                .from(user)
                .where(user.username.eq(username))
                .fetchOne();

休眠查询和错误：

Hibernate: 
    select
        user0_.password as col_0_0_,
        . as col_1_0_,    <----------------- HERE IS THE PROBLEM
        role2_.id as id1_7_,
        role2_.description as descript2_7_ 
    from
        user_acc user0_ 
    inner join
        user_role roles1_ 
            on user0_.id=roles1_.user_id 
    inner join
        role role2_ 
            on roles1_.role_id=role2_.id 
    where
        user0_.username=?
2020-09-09 22:24:11.367  WARN 41998 --- [nio-8080-exec-2] o.h.engine.jdbc.spi.SqlExceptionHelper   : SQL Error: 0, SQLState: 42601
2020-09-09 22:24:11.367 ERROR 41998 --- [nio-8080-exec-2] o.h.engine.jdbc.spi.SqlExceptionHelper   : ERROR: syntax error at or near "."
  Position: 37
2020-09-09 22:24:11.380 ERROR 41998 --- [nio-8080-exec-2] tUsernameAndPasswordAuthenticationFilter : An internal error occurred while trying to authenticate the user.

org.springframework.security.authentication.InternalAuthenticationServiceException: could not extract ResultSet; SQL [n/a]; nested exception is org.hibernate.exception.SQLGrammarException: could not extract ResultSet
    at org.springframework.security.authentication.dao.DaoAuthenticationProvider.retrieveUser(DaoAuthenticationProvider.java:123) ~[spring-security-core-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.authentication.dao.AbstractUserDetailsAuthenticationProvider.authenticate(AbstractUserDetailsAuthenticationProvider.java:144) ~[spring-security-core-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.authentication.ProviderManager.authenticate(ProviderManager.java:175) ~[spring-security-core-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at com.rooms.jwt.JwtUsernameAndPasswordAuthenticationFilter.attemptAuthentication(JwtUsernameAndPasswordAuthenticationFilter.java:39) ~[classes/:na]
    at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:212) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:116) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.header.HeaderWriterFilter.doHeadersAfter(HeaderWriterFilter.java:92) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:77) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:105) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:56) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:334) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:215) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:178) ~[spring-security-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:358) ~[spring-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:271) ~[spring-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:526) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:861) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1579) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) ~[na:na]
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) ~[na:na]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-9.0.27.jar:9.0.27]
    at java.base/java.lang.Thread.run(Thread.java:834) ~[na:na]
Caused by: org.springframework.dao.InvalidDataAccessResourceUsageException: could not extract ResultSet; SQL [n/a]; nested exception is org.hibernate.exception.SQLGrammarException: could not extract ResultSet
    at org.springframework.orm.jpa.vendor.HibernateJpaDialect.convertHibernateAccessException(HibernateJpaDialect.java:281) ~[spring-orm-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.orm.jpa.vendor.HibernateJpaDialect.translateExceptionIfPossible(HibernateJpaDialect.java:255) ~[spring-orm-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.translateExceptionIfPossible(AbstractEntityManagerFactoryBean.java:528) ~[spring-orm-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.dao.support.ChainedPersistenceExceptionTranslator.translateExceptionIfPossible(ChainedPersistenceExceptionTranslator.java:61) ~[spring-tx-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.dao.support.DataAccessUtils.translateIfNecessary(DataAccessUtils.java:242) ~[spring-tx-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:153) ~[spring-tx-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:747) ~[spring-aop-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:689) ~[spring-aop-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at com.rooms.auth.ApplicationUserDaoService$$EnhancerBySpringCGLIB$$9df7f693.selectApplicationUserByUsername(<generated>) ~[classes/:na]
    at com.rooms.auth.ApplicationUserService.loadUserByUsername(ApplicationUserService.java:21) ~[classes/:na]
    at org.springframework.security.authentication.dao.DaoAuthenticationProvider.retrieveUser(DaoAuthenticationProvider.java:108) ~[spring-security-core-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    ... 50 common frames omitted
Caused by: org.hibernate.exception.SQLGrammarException: could not extract ResultSet
    at org.hibernate.exception.internal.SQLStateConversionDelegate.convert(SQLStateConversionDelegate.java:103) ~[hibernate-core-5.4.14.Final.jar:5.4.14.Final]
    at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:42) ~[hibernate-core-5.4.14.Final.jar:5.4.14.Final]
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:113) ~[hibernate-core-5.4.14.Final.jar:5.4.14.Final]
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:99) ~[hibernate-core-5.4.14.Final.jar:5.4.14.Final]
    at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.extract(ResultSetReturnImpl.java:67) ~[hibernate-core-5.4.14.Final.jar:5.4.14.Final]
    at org.hibernate.loader.Loader.getResultSet(Loader.java:2292) ~[hibernate-core-5.4.14.Final.jar:5.4.14.Final]
    at org.hibernate.loader.Loader.executeQueryStatement(Loader.java:2050) ~[hibernate-core-5.4.14.Final.jar:5.4.14.Final]
    at org.hibernate.loader.Loader.executeQueryStatement(Loader.java:2012) ~[hibernate-core-5.4.14.Final.jar:5.4.14.Final]
    at org.hibernate.loader.Loader.doQuery(Loader.java:953) ~[hibernate-core-5.4.14.Final.jar:5.4.14.Final]
    at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:354) ~[hibernate-core-5.4.14.Final.jar:5.4.14.Final]
    at org.hibernate.loader.Loader.doList(Loader.java:2838) ~[hibernate-core-5.4.14.Final.jar:5.4.14.Final]
    at org.hibernate.loader.Loader.doList(Loader.java:2820) ~[hibernate-core-5.4.14.Final.jar:5.4.14.Final]
    at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2652) ~[hibernate-core-5.4.14.Final.jar:5.4.14.Final]
    at org.hibernate.loader.Loader.list(Loader.java:2647) ~[hibernate-core-5.4.14.Final.jar:5.4.14.Final]
    at org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:506) ~[hibernate-core-5.4.14.Final.jar:5.4.14.Final]
    at org.hibernate.hql.internal.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:396) ~[hibernate-core-5.4.14.Final.jar:5.4.14.Final]
    at org.hibernate.engine.query.spi.HQLQueryPlan.performList(HQLQueryPlan.java:219) ~[hibernate-core-5.4.14.Final.jar:5.4.14.Final]
    at org.hibernate.internal.SessionImpl.list(SessionImpl.java:1404) ~[hibernate-core-5.4.14.Final.jar:5.4.14.Final]
    at org.hibernate.query.internal.AbstractProducedQuery.doList(AbstractProducedQuery.java:1565) ~[hibernate-core-5.4.14.Final.jar:5.4.14.Final]
    at org.hibernate.query.internal.AbstractProducedQuery.list(AbstractProducedQuery.java:1533) ~[hibernate-core-5.4.14.Final.jar:5.4.14.Final]
    at org.hibernate.query.internal.AbstractProducedQuery.getSingleResult(AbstractProducedQuery.java:1581) ~[hibernate-core-5.4.14.Final.jar:5.4.14.Final]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
    at org.springframework.orm.jpa.SharedEntityManagerCreator$DeferredQueryInvocationHandler.invoke(SharedEntityManagerCreator.java:409) ~[spring-orm-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at com.sun.proxy.$Proxy161.getSingleResult(Unknown Source) ~[na:na]
    at com.querydsl.jpa.impl.AbstractJPAQuery.getSingleResult(AbstractJPAQuery.java:173) ~[querydsl-jpa-4.2.1.jar:na]
    at com.querydsl.jpa.impl.AbstractJPAQuery.fetchOne(AbstractJPAQuery.java:253) ~[querydsl-jpa-4.2.1.jar:na]
    at com.rooms.auth.ApplicationUserDaoService.selectApplicationUserByUsername(ApplicationUserDaoService.java:61) ~[classes/:na]
    at com.rooms.auth.ApplicationUserDaoService$$FastClassBySpringCGLIB$$c677177b.invoke(<generated>) ~[classes/:na]
    at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218) ~[spring-core-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:769) ~[spring-aop-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163) ~[spring-aop-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:747) ~[spring-aop-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:139) ~[spring-tx-5.2.1.RELEASE.jar:5.2.1.RELEASE]
    ... 56 common frames omitted
Caused by: org.postgresql.util.PSQLException: ERROR: syntax error at or near "."
  Position: 37
    at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:2497) ~[postgresql-42.2.8.jar:42.2.8]
    at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:2233) ~[postgresql-42.2.8.jar:42.2.8]
    at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:310) ~[postgresql-42.2.8.jar:42.2.8]
    at org.postgresql.jdbc.PgStatement.executeInternal(PgStatement.java:446) ~[postgresql-42.2.8.jar:42.2.8]
    at org.postgresql.jdbc.PgStatement.execute(PgStatement.java:370) ~[postgresql-42.2.8.jar:42.2.8]
    at org.postgresql.jdbc.PgPreparedStatement.executeWithFlags(PgPreparedStatement.java:149) ~[postgresql-42.2.8.jar:42.2.8]
    at org.postgresql.jdbc.PgPreparedStatement.executeQuery(PgPreparedStatement.java:108) ~[postgresql-42.2.8.jar:42.2.8]
    at com.zaxxer.hikari.pool.ProxyPreparedStatement.executeQuery(ProxyPreparedStatement.java:52) ~[HikariCP-3.4.1.jar:na]
    at com.zaxxer.hikari.pool.HikariProxyPreparedStatement.executeQuery(HikariProxyPreparedStatement.java) ~[HikariCP-3.4.1.jar:na]
    at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.extract(ResultSetReturnImpl.java:57) ~[hibernate-core-5.4.14.Final.jar:5.4.14.Final]
    ... 87 common frames omitted

我的角色类只有一个 id 和 description 属性，它与用户是多对多的关系。

如果我只将投影更改为密码，它可以正常工作但使用角色，queryDSL 通过那个奇怪的“。”询问数据库。除了 role.id 和 role.description，我不知道为什么。

有人可以帮助我吗？我在互联网上找不到任何关于这种行为的信息，我不知道我做错了什么。

提前谢谢你。

【问题讨论】：

【参考方案1】：

问题是您的查询返回平面关系对象列表password-role。 EntityManager 仅为实体转换平面关系。至于projection的结果，你必须手动转换。

你需要dto这样的类

public class PasswordRole 

    private String password;
    private Role role;

    public UserAuth(String password, Role role) 
        this.password = password;
        this.role = role;
    

    //getters

您的查询

String username = "Tom";
QUser user = QUser.user;
QRole role = QRole.role;

JPAQueryFactory queryFactory = new JPAQueryFactory(entityManager);
List<PasswordRole> passwordRoles = queryFactory
                .select(Projections.constructor(PasswordRole.class, user.password, role))
                .from(user)
                .join(user.roles, role)
                .where(user.username.eq(username))
                .fetch();

然后你必须将List<PasswordRole> 转换为UserAuth

public UserAuth toUserAuth(List<PasswordRole> passwordRoles) 
   if(passwordRoles.isEmpty()) 
       throw new IllegalArgumentException("empty list of passwordRoles");
   

   Set<Role> roles = passwordRoles.stream().map(PasswordRole::getRole)
                                  .distinct().collect(Collectors.toSet());

   return new UserAuth(passwordRoles.get(0).getPassword(), roles);

【讨论】：

非常感谢，它有效:) 一个问题，使用这种方法，当我们从数据库中获取数据时，密码将与关联角色的数量一样多，即：( password:123, Role:Basic; password: 123, role: Premium; password 123, role: Admin ...) 在获取数据库中的数据？数据库只能返回平面数据。有一些特定的数据库相关函数（例如 mysql GROUP_CONCAT）。但一般来说是不可能的。 Entity manager 可以将平面查询结果转化为实体。

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