FluxOnAssembly cannot be cast to java.lang.Iterable

Bug report Hi everyone! I wanted to try out new the new spring boot 2.0.0 M7 with reactive web and rest repositories. I have a very minimal setup with a normal mongo document and a simple reactive repository like bellow:

@Repository
@RepositoryRestResource
public interface PostRepository extends ReactiveMongoRepository<Post, String> {
}

@Document
@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
public class Post {
    @Id
    @JsonProperty(access = READ_ONLY)
    private String id;

    @NotEmpty
    @Length(max = 300)
    private String title;

    @NotEmpty
    private String description;

    private Instant createdAt = Instant.now();
    private Instant updatedAt = Instant.now();
}

After going to http://localhost:8080/posts I’m getting such errors:

java.lang.ClassCastException: reactor.core.publisher.FluxOnAssembly cannot be cast to java.lang.Iterable
	at org.springframework.data.repository.support.ReflectionRepositoryInvoker.invokeFindAllReflectively(ReflectionRepositoryInvoker.java:327) ~[spring-data-commons-2.0.2.RELEASE.jar:2.0.2.RELEASE]
	at org.springframework.data.repository.support.ReflectionRepositoryInvoker.invokeFindAll(ReflectionRepositoryInvoker.java:92) ~[spring-data-commons-2.0.2.RELEASE.jar:2.0.2.RELEASE]
	at org.springframework.data.repository.support.ReflectionRepositoryInvoker.invokeFindAllReflectively(ReflectionRepositoryInvoker.java:315) ~[spring-data-commons-2.0.2.RELEASE.jar:2.0.2.RELEASE]
	at org.springframework.data.repository.support.ReflectionRepositoryInvoker.invokeFindAll(ReflectionRepositoryInvoker.java:101) ~[spring-data-commons-2.0.2.RELEASE.jar:2.0.2.RELEASE]
	at org.springframework.data.rest.core.support.UnwrappingRepositoryInvokerFactory$UnwrappingRepositoryInvoker.invokeFindAll(UnwrappingRepositoryInvokerFactory.java:161) ~[spring-data-rest-core-3.0.2.RELEASE.jar:3.0.2.RELEASE]
	at org.springframework.data.rest.webmvc.RepositoryEntityController.getCollectionResource(RepositoryEntityController.java:202) ~[spring-data-rest-webmvc-3.0.2.RELEASE.jar:3.0.2.RELEASE]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_131]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_131]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_131]
	at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_131]
	at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:209) ~[spring-web-5.0.2.RELEASE.jar:5.0.2.RELEASE]
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136) ~[spring-web-5.0.2.RELEASE.jar:5.0.2.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102) ~[spring-webmvc-5.0.2.RELEASE.jar:5.0.2.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:871) ~[spring-webmvc-5.0.2.RELEASE.jar:5.0.2.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:777) ~[spring-webmvc-5.0.2.RELEASE.jar:5.0.2.RELEASE]
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.0.2.RELEASE.jar:5.0.2.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:991) ~[spring-webmvc-5.0.2.RELEASE.jar:5.0.2.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:925) ~[spring-webmvc-5.0.2.RELEASE.jar:5.0.2.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:978) [spring-webmvc-5.0.2.RELEASE.jar:5.0.2.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:870) [spring-webmvc-5.0.2.RELEASE.jar:5.0.2.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:635) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:855) [spring-webmvc-5.0.2.RELEASE.jar:5.0.2.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) [tomcat-embed-websocket-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) [spring-web-5.0.2.RELEASE.jar:5.0.2.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.2.RELEASE.jar:5.0.2.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:108) [spring-web-5.0.2.RELEASE.jar:5.0.2.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.2.RELEASE.jar:5.0.2.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:81) [spring-web-5.0.2.RELEASE.jar:5.0.2.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.2.RELEASE.jar:5.0.2.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) [spring-web-5.0.2.RELEASE.jar:5.0.2.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-5.0.2.RELEASE.jar:5.0.2.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:478) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_131]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_131]
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.23.jar:8.5.23]
	at java.lang.Thread.run(Thread.java:748) [na:1.8.0_131]

[odrotbohm]

It’s not compatible with WebFlux (as that basically needs a rewrite), but it’s of course to Spring MVC based apps built with Boot 2.0.

[odrotbohm]

I’ve left a comment about the current state of affairs in the corresponding ticket in Spring Data REST’s tracker.