'Using Closed Projection in Spring Data JPA failed with MappingException

I try to get a subset of attributes from a JPA entity Data by using interface-based Projection in Spring Data JPA to minimize the JSON response data of an HTTP request from my frontend (Angular).

Using Closed Projection seems a good approach to handle that - simple to implement and easy to maintain.

public interface DataRepository extends JpaRepository<Data, Long> {
    List<DataView> findByLocation(String location))

    interface DataView {
        String getLocation();
    }
}

I'm using JpaRepository to get the full scope of the Spring Data Repository functionality but I receive the following exception in my Tomcat console:

org.springframework.data.mapping.MappingException: Couldn't find PersistentEntity for type class com.sun.proxy.$Proxy121!
    at org.springframework.data.mapping.context.MappingContext.getRequiredPersistentEntity(MappingContext.java:79) ~[spring-data-commons-2.5.2.jar:2.5.2]
    at org.springframework.data.mapping.context.PersistentEntities.getRequiredPersistentEntity(PersistentEntities.java:115) ~[spring-data-commons-2.5.2.jar:2.5.2]
    at org.springframework.data.rest.webmvc.PersistentEntityResourceAssembler.wrap(PersistentEntityResourceAssembler.java:90) ~[spring-data-rest-webmvc-3.5.2.jar:3.5.2]
    at org.springframework.data.rest.webmvc.PersistentEntityResourceAssembler.toModel(PersistentEntityResourceAssembler.java:73) ~[spring-data-rest-webmvc-3.5.2.jar:3.5.2]
    at org.springframework.data.rest.webmvc.AbstractRepositoryRestController.entitiesToResources(AbstractRepositoryRestController.java:110) ~[spring-data-rest-webmvc-3.5.2.jar:3.5.2]
    at org.springframework.data.rest.webmvc.AbstractRepositoryRestController.toCollectionModel(AbstractRepositoryRestController.java:80) ~[spring-data-rest-webmvc-3.5.2.jar:3.5.2]
    at org.springframework.data.rest.webmvc.RepositorySearchController.lambda$toModel$1(RepositorySearchController.java:204) ~[spring-data-rest-webmvc-3.5.2.jar:3.5.2]
    at java.base/java.util.Optional.map(Optional.java:258) ~[na:na]
    at org.springframework.data.rest.webmvc.RepositorySearchController.toModel(RepositorySearchController.java:201) ~[spring-data-rest-webmvc-3.5.2.jar:3.5.2]
    at org.springframework.data.rest.webmvc.RepositorySearchController.executeSearch(RepositorySearchController.java:185) ~[spring-data-rest-webmvc-3.5.2.jar:3.5.2]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:64) ~[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:564) ~[na:na]
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:197) ~[spring-web-5.3.8.jar:5.3.8]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:141) ~[spring-web-5.3.8.jar:5.3.8]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:106) ~[spring-webmvc-5.3.8.jar:5.3.8]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:894) ~[spring-webmvc-5.3.8.jar:5.3.8]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808) ~[spring-webmvc-5.3.8.jar:5.3.8]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.3.8.jar:5.3.8]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1063) ~[spring-webmvc-5.3.8.jar:5.3.8]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:963) ~[spring-webmvc-5.3.8.jar:5.3.8]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.3.8.jar:5.3.8]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) ~[spring-webmvc-5.3.8.jar:5.3.8]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:655) ~[servlet-api.jar:4.0.FR]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.3.8.jar:5.3.8]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:764) ~[servlet-api.jar:4.0.FR]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227) ~[catalina.jar:9.0.56]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[catalina.jar:9.0.56]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-websocket.jar:9.0.56]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[catalina.jar:9.0.56]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[catalina.jar:9.0.56]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.3.8.jar:5.3.8]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.8.jar:5.3.8]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[catalina.jar:9.0.56]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[catalina.jar:9.0.56]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.3.8.jar:5.3.8]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.8.jar:5.3.8]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[catalina.jar:9.0.56]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[catalina.jar:9.0.56]
    at org.springframework.boot.web.servlet.support.ErrorPageFilter.doFilter(ErrorPageFilter.java:126) ~[spring-boot-2.5.2.jar:2.5.2]
    at org.springframework.boot.web.servlet.support.ErrorPageFilter.access$000(ErrorPageFilter.java:64) ~[spring-boot-2.5.2.jar:2.5.2]
    at org.springframework.boot.web.servlet.support.ErrorPageFilter$1.doFilterInternal(ErrorPageFilter.java:101) ~[spring-boot-2.5.2.jar:2.5.2]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.8.jar:5.3.8]
    at org.springframework.boot.web.servlet.support.ErrorPageFilter.doFilter(ErrorPageFilter.java:119) ~[spring-boot-2.5.2.jar:2.5.2]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[catalina.jar:9.0.56]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[catalina.jar:9.0.56]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.3.8.jar:5.3.8]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.3.8.jar:5.3.8]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[catalina.jar:9.0.56]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[catalina.jar:9.0.56]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:197) ~[catalina.jar:9.0.56]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) ~[catalina.jar:9.0.56]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:540) ~[catalina.jar:9.0.56]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135) ~[catalina.jar:9.0.56]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) ~[catalina.jar:9.0.56]
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:687) ~[catalina.jar:9.0.56]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) ~[catalina.jar:9.0.56]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:357) ~[catalina.jar:9.0.56]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:382) ~[tomcat-coyote.jar:9.0.56]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) ~[tomcat-coyote.jar:9.0.56]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:895) ~[tomcat-coyote.jar:9.0.56]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1732) ~[tomcat-coyote.jar:9.0.56]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-coyote.jar:9.0.56]
    at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191) ~[tomcat-util.jar:9.0.56]
    at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659) ~[tomcat-util.jar:9.0.56]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-util.jar:9.0.56]
    at java.base/java.lang.Thread.run(Thread.java:832) ~[na:na]

I read that "Behind the scenes, Spring creates a proxy instance of the projection interface for each entity object, and all calls to the proxy are forwarded to that object."

What am I doing wrong here?

If you need more information, please let me know.

Thanks in advance for your help!

Edit

I've noticed that I get a CORS error 'Access-Control-Allow-Origin' if the frontend request the URL. I assume that the response is some kind of cross origin. Is this caused by the proxy instance I pointed out before? That would be a really strange behaviour. I will try to add cors.allowed.headers to the dev tomcat instance and check that out.

Result of applying CORS filter

Same error as before if I add http://localhost:8080 or http://localhost:4200 to dev pr prod tomcat instance web.xml. I think, the proxy instance refers to another URL. Anyone has an idea?

<filter>
      <filter-name>CorsFilter</filter-name>
      <filter-class>org.apache.catalina.filters.CorsFilter</filter-class>
      <init-param>
        <param-name>cors.allowed.origins</param-name>
        <param-value>http://localhost:4200,http://localhost:8080</param-value>
      </init-param>
      <init-param>
        <param-name>cors.allowed.headers</param-name>
        <param-value>Content-Type,X-Requested-With,accept,Origin,Access-Control-Request-Method,Access-Control-Request-Headers,Access-Control-Allow-Origin</param-value>
      </init-param>
      <init-param>
        <param-name>cors.exposed.headers</param-name>
        <param-value>Access-Control-Allow-Origin</param-value>
      </init-param>
    </filter>
    <filter-mapping>
      <filter-name>CorsFilter</filter-name>
      <url-pattern>/*</url-pattern>
    </filter-mapping>

Solution 1:^[1]

The class Data must be a JPA entity. I'm doubting that Data is just a normal DTO class. The ID of entity Data is of the type Long and the parameter Integer is used to query the entity. @RequestParam is used in a controller and it is not needed here. findById already exists in CRUD repository, it is not recommended to override it. It is better to use another method name. The repository name is SensorDataRepository, it means it is meant to manage the entity SensorData rather than the entity Data.

The repository and projection interface should look something like below.

public interface DataRepository extends JpaRepository<Data, Long> {
    List<DataView> findDataViewById(Long id);

    interface DataView {
        Long getId(); // if the field name is `id`, the method name should be `getId()`
    }
}

Solution 2:^[2]

If spring-data-rest projection is fine instead of JPA projection

try

moving the DataView interface class to the same package where the Data entity is located
and add the following annotation on top of the DataView class @Projection(name = "dataView", types = Data.class)
then add the ?projection=dataView query param to your search url

for example:

http://localhost:8080/data/search/findByLocation?location=someplace&projection=dataView

Solution 3:^[3]

I came up with a new approach to find a solution to minimize the JSON response data of an HTTP request. The key word is Cache requests. It's not fixing my requested question but solved the general issue I have.

Right now, I'm caching nothing in my web app. So, for every change of navigation that causes an HTTP request, it asks the backend for data. Kind of bad behaviour.

That should be a good solution avoiding 95% of network traffic. Pretty stupid when I rethink my previous approach to just responding a subset of attributes from an entity... :)

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution	Source
Solution 1	atish.s
Solution 2
Solution 3

'Using Closed Projection in Spring Data JPA failed with MappingException

Solution 1:[1]

Solution 2:[2]

Solution 3:[3]

Sources

Related Questions

Solution 1:^[1]

Solution 2:^[2]

Solution 3:^[3]