I would require ecm:mixinType and dc:subjects in a custom JSON output. The Repository.ResultSetPageProvider works well for me as long as I have no multivalued properties. Is there any chance to include the fields as the default query throws an error?

{"params":{"language":"NXQL","query":"SELECT ecm:uuid, ecm:primaryType, ecm:mixinType FROM Document WHERE ecm:ancestorId = '67614484-3e36-472d-ab21-a9ebc5a1e0c4' AND ecm:primaryType = 'File' AND ecm:isProxy = 0 AND ecm:isCheckedInVersion = 0","sortInfo":"dc:title","sortOrder":"ASC"},"context":{}}
2017-07-04 15:57:18,320 WARN [http-apr-0.0.0.0-8080-exec-23] [org.nuxeo.ecm.webengine.app.WebEngineExceptionMapper] Exception in JAX-RS processing org.nuxeo.ecm.webengine.WebException: Failed to invoke operation: Repository.ResultSetPageProvider at org.nuxeo.ecm.webengine.WebException.newException(WebException.java:133) at org.nuxeo.ecm.webengine.WebException.newException(WebException.java:122) at org.nuxeo.ecm.automation.server.jaxrs.ExecutableResource.doPost(ExecutableResource.java:87) at sun.reflect.GeneratedMethodAccessor1500.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at com.sun.jersey.spi.container.JavaMethodInvokerFactory$1.invoke(JavaMethodInvokerFactory.java:60) at com.sun.jersey.server.impl.model.method.dispatch.AbstractResourceMethodDispatchProvider$ObjectOutInvoker._dispatch(AbstractResourceMethodDispatchProvider.java:258) at com.sun.jersey.server.impl.model.method.dispatch.ResourceJavaMethodDispatcher.dispatch(ResourceJavaMethodDispatcher.java:75) at com.sun.jersey.server.impl.uri.rules.HttpMethodRule.accept(HttpMethodRule.java:302) at com.sun.jersey.server.impl.uri.rules.SubLocatorRule.accept(SubLocatorRule.java:137) at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147) at com.sun.jersey.server.impl.uri.rules.ResourceClassRule.accept(ResourceClassRule.java:108) at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147) at com.sun.jersey.server.impl.uri.rules.RootResourceClassesRule.accept(RootResourceClassesRule.java:84) at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1542) at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1473) at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1419) at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1409) at com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:409) at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:558) at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:733) at org.nuxeo.ecm.webengine.app.jersey.WebEngineServlet.containerService(WebEngineServlet.java:178) at org.nuxeo.ecm.webengine.app.jersey.WebEngineServlet.service(WebEngineServlet.java:155) at javax.servlet.http.HttpServlet.service(HttpServlet.java:731) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) at org.nuxeo.elasticsearch.ElasticSearchFilter.doFilter(ElasticSearchFilter.java:55) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) at org.nuxeo.ecm.webengine.jaxrs.session.SessionCleanupFilter.run(SessionCleanupFilter.java:50) at org.nuxeo.ecm.webengine.jaxrs.HttpFilter.doFilter(HttpFilter.java:49) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) at org.nuxeo.ecm.webengine.app.WebEngineFilter.doFilter(WebEngineFilter.java:92) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) at org.nuxeo.ecm.webengine.jaxrs.context.RequestContextFilter.run(RequestContextFilter.java:48) at org.nuxeo.ecm.webengine.jaxrs.HttpFilter.doFilter(HttpFilter.java:49) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) at org.nuxeo.ecm.platform.web.common.requestcontroller.filter.NuxeoThreadTrackerFilter.doFilter(NuxeoThreadTrackerFilter.java:43) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) at org.nuxeo.ecm.core.management.jtajca.internal.Log4jWebFilter.doFilter(Log4jWebFilter.java:69) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) at org.nuxeo.ecm.platform.ui.web.rest.FancyURLFilter.doFilter(FancyURLFilter.java:120) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) at org.nuxeo.ecm.platform.web.common.requestcontroller.filter.NuxeoRequestControllerFilter.doFilter(NuxeoRequestControllerFilter.java:146) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) at org.nuxeo.ecm.webdav.service.WIRequestFilter.doFilter(WIRequestFilter.java:61) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) at org.nuxeo.ecm.platform.ui.web.auth.NuxeoAuthenticationFilter.doFilterInternal(NuxeoAuthenticationFilter.java:598) at org.nuxeo.ecm.platform.ui.web.auth.service.NuxeoAuthFilterChain.doFilter(NuxeoAuthFilterChain.java:51) at org.nuxeo.ecm.platform.ui.web.auth.oauth.NuxeoOAuthFilter.doFilter(NuxeoOAuthFilter.java:122) at org.nuxeo.ecm.platform.ui.web.auth.service.NuxeoAuthFilterChain.doFilter(NuxeoAuthFilterChain.java:49) at org.nuxeo.ecm.platform.ui.web.auth.oauth2.NuxeoOAuth2Filter.doFilter(NuxeoOAuth2Filter.java:83) at org.nuxeo.ecm.platform.ui.web.auth.service.NuxeoAuthFilterChain.doFilter(NuxeoAuthFilterChain.java:49) at org.nuxeo.ecm.platform.ui.web.auth.NuxeoAuthenticationFilter.doFilter(NuxeoAuthenticationFilter.java:408) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) at com.thetransactioncompany.cors.CORSFilter.doFilter(CORSFilter.java:208) at com.thetransactioncompany.cors.CORSFilter.doFilter(CORSFilter.java:274) at org.nuxeo.ecm.platform.web.common.requestcontroller.filter.NuxeoCorsFilter.doFilter(NuxeoCorsFilter.java:49) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) at org.nuxeo.ecm.platform.web.common.exceptionhandling.NuxeoExceptionFilter.doFilter(NuxeoExceptionFilter.java:77) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) at org.nuxeo.ecm.platform.web.common.encoding.NuxeoEncodingFilter.doFilter(NuxeoEncodingFilter.java:75) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:436) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1078) at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:625) at org.apache.tomcat.util.net.AprEndpoint$SocketWithOptionsProcessor.run(AprEndpoint.java:2454) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Thread.java:745) Caused by: org.nuxeo.ecm.automation.TraceException: ****** chain ****** Name: Repository.ResultSetPageProvider Aliases: [Resultset.PageProvider] Exception: OperationException Caught error: Failed to execute query: NXQL: SELECT ecm:uuid, ecm:primaryType, ecm:mixinType FROM Document WHERE ecm:ancestorId = '67614484-3e36-472d-ab21-a9ebc5a1e0c4' AND ecm:primaryType = 'File' AND ecm:isProxy = 0 AND ecm:isCheckedInVersion = 0 ORDER BY dc:title, Cannot select on column: ecm:mixinType Caused by: null ****** Hierarchy calls ****** org.nuxeo.ecm.automation.core.operations.services.ResultSetPageProviderOperation at org.nuxeo.ecm.automation.core.impl.OperationServiceImpl.run(OperationServiceImpl.java:234) at org.nuxeo.ecm.automation.core.impl.OperationServiceImpl.run(OperationServiceImpl.java:117) at org.nuxeo.ecm.automation.server.jaxrs.OperationResource.execute(OperationResource.java:58) at org.nuxeo.ecm.automation.server.jaxrs.ExecutableResource.doPost(ExecutableResource.java:68) ... 90 more Caused by: org.nuxeo.ecm.automation.OperationException: Failed to execute query: NXQL: SELECT ecm:uuid, ecm:primaryType, ecm:mixinType FROM Document WHERE ecm:ancestorId = '67614484-3e36-472d-ab21-a9ebc5a1e0c4' AND ecm:primaryType = 'File' AND ecm:isProxy = 0 AND ecm:isCheckedInVersion = 0 ORDER BY dc:title, Cannot select on column: ecm:mixinType at org.nuxeo.ecm.automation.core.operations.services.ResultSetPageProviderOperation.run(ResultSetPageProviderOperation.java:244) at sun.reflect.GeneratedMethodAccessor2293.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.nuxeo.ecm.automation.core.impl.InvokableMethod.doInvoke(InvokableMethod.java:164) at org.nuxeo.ecm.automation.core.impl.InvokableMethod.invoke(InvokableMethod.java:177) at org.nuxeo.ecm.automation.core.impl.CompiledChainImpl.doInvoke(CompiledChainImpl.java:130) at org.nuxeo.ecm.automation.core.impl.CompiledChainImpl.invoke(CompiledChainImpl.java:116) at org.nuxeo.ecm.automation.core.impl.OperationServiceImpl.run(OperationServiceImpl.java:210) ... 93 more