From eade858ece492b1d6fb4ccd47585f6367928aced Mon Sep 17 00:00:00 2001
From: Ziroli <no_reply@ziz.ch>
Date: Fri, 6 Mar 2026 15:11:23 +0100
Subject: [PATCH] feat(QueryPage): support CONSTRUCT queries (#380)

Upgrade nanopub-java to 1.86.1 which adds processRdfContent(Model) to
QueryAccess, allowing CONSTRUCT query results to be received as an RDF
Model rather than tabular CSV data.

- GrlcQuery: add isConstructQuery() detecting ParsedGraphQuery
- ApiCache: add cachedRdfModels and retrieveRdfModelAsync() using the
  new processRdfContent hook
- RdfResultComponent: async lazy-loader for RDF model results
- QueryResultRdf: panel displaying CONSTRUCT results as a paginated
  Subject/Predicate/Object table with NanodashLink for URIs
- QueryPage: route CONSTRUCT queries to QueryResultRdf

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 pom.xml                                       |   2 +-
 .../knowledgepixels/nanodash/ApiCache.java    |  81 +++++++++++++
 .../knowledgepixels/nanodash/GrlcQuery.java   |  12 ++
 .../nanodash/component/QueryResultRdf.html    |  16 +++
 .../nanodash/component/QueryResultRdf.java    | 110 ++++++++++++++++++
 .../component/RdfResultComponent.java         |  65 +++++++++++
 .../nanodash/page/QueryPage.java              |  18 +++
 7 files changed, 303 insertions(+), 1 deletion(-)
 create mode 100644 src/main/java/com/knowledgepixels/nanodash/component/QueryResultRdf.html
 create mode 100644 src/main/java/com/knowledgepixels/nanodash/component/QueryResultRdf.java
 create mode 100644 src/main/java/com/knowledgepixels/nanodash/component/RdfResultComponent.java

diff --git a/pom.xml b/pom.xml
index f9b49340..1cce8f2b 100644
--- a/pom.xml
+++ b/pom.xml
@@ -101,7 +101,7 @@
     <dependency>
       <groupId>org.nanopub</groupId>
       <artifactId>nanopub</artifactId>
-      <version>1.86.0</version>
+      <version>1.86.1</version>
     </dependency>
     <!-- Temporary: dependency on Jitpack for snapshot builds -->
     <!-- <dependency>
diff --git a/src/main/java/com/knowledgepixels/nanodash/ApiCache.java b/src/main/java/com/knowledgepixels/nanodash/ApiCache.java
index 2b2d674e..70242158 100644
--- a/src/main/java/com/knowledgepixels/nanodash/ApiCache.java
+++ b/src/main/java/com/knowledgepixels/nanodash/ApiCache.java
@@ -1,5 +1,6 @@
 package com.knowledgepixels.nanodash;
 
+import org.eclipse.rdf4j.model.Model;
 import org.nanopub.extra.services.*;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -21,6 +22,7 @@ private ApiCache() {
     } // no instances allowed
 
     private transient static ConcurrentMap<String, ApiResponse> cachedResponses = new ConcurrentHashMap<>();
+    private transient static ConcurrentMap<String, Model> cachedRdfModels = new ConcurrentHashMap<>();
     private transient static ConcurrentMap<String, Integer> failed = new ConcurrentHashMap<>();
     private transient static ConcurrentMap<String, Map<String, String>> cachedMaps = new ConcurrentHashMap<>();
     private transient static ConcurrentMap<String, Long> lastRefresh = new ConcurrentHashMap<>();
@@ -242,6 +244,85 @@ public static synchronized Map<String, String> retrieveMap(QueryRef queryRef) {
         }
     }
 
+    private static void updateRdfModel(QueryRef queryRef) throws FailedApiCallException, APINotReachableException, NotEnoughAPIInstancesException {
+        final Model[] modelRef = new Model[1];
+        QueryAccess qa = new QueryAccess() {
+            @Override
+            protected void processHeader(String[] line) {}
+            @Override
+            protected void processLine(String[] line) {}
+            @Override
+            protected void processRdfContent(Model model) {
+                modelRef[0] = model;
+            }
+        };
+        qa.call(queryRef);
+        if (modelRef[0] == null) {
+            throw new FailedApiCallException(new Exception("No RDF content in response for query: " + queryRef.getQueryId()));
+        }
+        String cacheId = queryRef.getAsUrlString();
+        logger.info("Updating cached RDF model for {}", cacheId);
+        cachedRdfModels.put(cacheId, modelRef[0]);
+        lastRefresh.put(cacheId, System.currentTimeMillis());
+    }
+
+    /**
+     * Retrieves a cached RDF model for a CONSTRUCT query, triggering a background fetch if needed.
+     *
+     * @param queryRef The QueryRef for the CONSTRUCT query.
+     * @return The cached RDF Model, or null if not yet available.
+     */
+    public static Model retrieveRdfModelAsync(QueryRef queryRef) {
+        long timeNow = System.currentTimeMillis();
+        String cacheId = queryRef.getAsUrlString();
+        logger.info("Retrieving cached RDF model asynchronously for {}", cacheId);
+        boolean isCached = false;
+        boolean needsRefresh = true;
+        if (cachedRdfModels.containsKey(cacheId) && cachedRdfModels.get(cacheId) != null) {
+            long cacheAge = timeNow - lastRefresh.get(cacheId);
+            isCached = cacheAge < 24 * 60 * 60 * 1000;
+            needsRefresh = cacheAge > 60 * 1000;
+        }
+        if (failed.get(cacheId) != null && failed.get(cacheId) > 2) {
+            failed.remove(cacheId);
+            throw new RuntimeException("Query failed: " + cacheId);
+        }
+        if (needsRefresh && !isRunning(cacheId)) {
+            refreshStart.put(cacheId, timeNow);
+            new Thread(() -> {
+                try {
+                    if (runAfter.containsKey(cacheId)) {
+                        while (System.currentTimeMillis() < runAfter.get(cacheId)) {
+                            Thread.sleep(100);
+                        }
+                        runAfter.remove(cacheId);
+                    }
+                    if (failed.get(cacheId) != null) {
+                        Thread.sleep(1000);
+                    }
+                    Thread.sleep(100 + new Random().nextLong(400));
+                } catch (InterruptedException ex) {
+                    logger.error("Interrupted while waiting to refresh RDF cache: {}", ex.getMessage());
+                }
+                try {
+                    updateRdfModel(queryRef);
+                } catch (Exception ex) {
+                    logger.error("Failed to update RDF cache for {}: {}", cacheId, ex.getMessage());
+                    cachedRdfModels.remove(cacheId);
+                    failed.merge(cacheId, 1, Integer::sum);
+                    lastRefresh.put(cacheId, System.currentTimeMillis());
+                } finally {
+                    refreshStart.remove(cacheId);
+                }
+            }).start();
+        }
+        if (isCached) {
+            return cachedRdfModels.get(cacheId);
+        } else {
+            return null;
+        }
+    }
+
     /**
      * Clears the cached response for a specific query reference and sets a delay before the next refresh can occur.
      *
diff --git a/src/main/java/com/knowledgepixels/nanodash/GrlcQuery.java b/src/main/java/com/knowledgepixels/nanodash/GrlcQuery.java
index 923a9430..cbf95465 100644
--- a/src/main/java/com/knowledgepixels/nanodash/GrlcQuery.java
+++ b/src/main/java/com/knowledgepixels/nanodash/GrlcQuery.java
@@ -10,6 +10,7 @@
 import org.eclipse.rdf4j.model.vocabulary.RDFS;
 import org.eclipse.rdf4j.query.algebra.Var;
 import org.eclipse.rdf4j.query.algebra.helpers.AbstractSimpleQueryModelVisitor;
+import org.eclipse.rdf4j.query.parser.ParsedGraphQuery;
 import org.eclipse.rdf4j.query.parser.ParsedQuery;
 import org.eclipse.rdf4j.query.parser.sparql.SPARQLParser;
 import org.nanopub.Nanopub;
@@ -85,6 +86,7 @@ public static GrlcQuery get(String id) {
     private String label;
     private String description;
     private final List<String> placeholdersList;
+    private boolean constructQuery;
 
     /**
      * Constructs a GrlcQuery object by parsing the provided query ID or URI.
@@ -139,6 +141,7 @@ private GrlcQuery(String id) {
 
         final Set<String> placeholders = new HashSet<>();
         ParsedQuery query = new SPARQLParser().parseQuery(sparql, null);
+        constructQuery = query instanceof ParsedGraphQuery;
         try {
             query.getTupleExpr().visitChildren(new AbstractSimpleQueryModelVisitor<Exception>() {
 
@@ -249,6 +252,15 @@ public List<String> getPlaceholdersList() {
         return placeholdersList;
     }
 
+    /**
+     * Returns true if this is a CONSTRUCT query (returns RDF graph data instead of tabular data).
+     *
+     * @return true if CONSTRUCT query
+     */
+    public boolean isConstructQuery() {
+        return constructQuery;
+    }
+
     /**
      * Creates a list of query parameter fields for the placeholders in the query.
      *
diff --git a/src/main/java/com/knowledgepixels/nanodash/component/QueryResultRdf.html b/src/main/java/com/knowledgepixels/nanodash/component/QueryResultRdf.html
new file mode 100644
index 00000000..88dd5a8b
--- /dev/null
+++ b/src/main/java/com/knowledgepixels/nanodash/component/QueryResultRdf.html
@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<html xmlns:wicket="http://wicket.apache.org">
+
+<head>
+  <link rel="stylesheet" href="../../../../../webapp/style.css?for-local-testing-only" type="text/css" media="screen"
+        title="Stylesheet"/>
+</head>
+<body>
+
+<wicket:panel>
+  <table wicket:id="table"></table>
+</wicket:panel>
+
+</body>
+
+</html>
diff --git a/src/main/java/com/knowledgepixels/nanodash/component/QueryResultRdf.java b/src/main/java/com/knowledgepixels/nanodash/component/QueryResultRdf.java
new file mode 100644
index 00000000..e8258891
--- /dev/null
+++ b/src/main/java/com/knowledgepixels/nanodash/component/QueryResultRdf.java
@@ -0,0 +1,110 @@
+package com.knowledgepixels.nanodash.component;
+
+import org.apache.wicket.extensions.ajax.markup.html.repeater.data.table.AjaxNavigationToolbar;
+import org.apache.wicket.extensions.markup.html.repeater.data.grid.ICellPopulator;
+import org.apache.wicket.extensions.markup.html.repeater.data.table.AbstractColumn;
+import org.apache.wicket.extensions.markup.html.repeater.data.table.DataTable;
+import org.apache.wicket.extensions.markup.html.repeater.data.table.HeadersToolbar;
+import org.apache.wicket.extensions.markup.html.repeater.data.table.NoRecordsToolbar;
+import org.apache.wicket.extensions.markup.html.repeater.data.sort.ISortState;
+import org.apache.wicket.extensions.markup.html.repeater.data.table.ISortableDataProvider;
+import org.apache.wicket.extensions.markup.html.repeater.util.SingleSortState;
+import org.apache.wicket.markup.html.basic.Label;
+import org.apache.wicket.markup.html.panel.Panel;
+import org.apache.wicket.markup.repeater.Item;
+import org.apache.wicket.model.IModel;
+import org.apache.wicket.model.Model;
+import org.eclipse.rdf4j.model.IRI;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+
+/**
+ * Component for displaying CONSTRUCT query results as a subject/predicate/object table.
+ */
+public class QueryResultRdf extends Panel {
+
+    public QueryResultRdf(String id, org.eclipse.rdf4j.model.Model rdfModel) {
+        super(id);
+
+        List<String[]> rows = new ArrayList<>();
+        for (org.eclipse.rdf4j.model.Statement st : rdfModel) {
+            rows.add(new String[]{
+                st.getSubject().stringValue(),
+                st.getPredicate().stringValue(),
+                st.getObject().stringValue()
+            });
+        }
+
+        List<AbstractColumn<String[], String>> columns = new ArrayList<>();
+        columns.add(new TripleColumn("Subject", 0));
+        columns.add(new TripleColumn("Predicate", 1));
+        columns.add(new TripleColumn("Object", 2));
+
+        DataTable<String[], String> table = new DataTable<>("table", columns, new TripleDataProvider(rows), 20);
+        table.addBottomToolbar(new AjaxNavigationToolbar(table));
+        table.addBottomToolbar(new NoRecordsToolbar(table));
+        table.addTopToolbar(new HeadersToolbar<>(table, null));
+        add(table);
+    }
+
+    private static class TripleDataProvider implements ISortableDataProvider<String[], String> {
+
+        private final List<String[]> rows;
+        private final SingleSortState<String> sortState = new SingleSortState<>();
+
+        TripleDataProvider(List<String[]> rows) {
+            this.rows = rows;
+        }
+
+        @Override
+        public Iterator<String[]> iterator(long first, long count) {
+            int f = (int) first;
+            int t = (int) Math.min(first + count, rows.size());
+            return rows.subList(f, t).iterator();
+        }
+
+        @Override
+        public long size() {
+            return rows.size();
+        }
+
+        @Override
+        public IModel<String[]> model(String[] object) {
+            return Model.of(object);
+        }
+
+        @Override
+        public ISortState<String> getSortState() {
+            return sortState;
+        }
+
+        @Override
+        public void detach() {
+        }
+
+    }
+
+    private static class TripleColumn extends AbstractColumn<String[], String> {
+
+        private final int index;
+
+        TripleColumn(String title, int index) {
+            super(new Model<>(title));
+            this.index = index;
+        }
+
+        @Override
+        public void populateItem(Item<ICellPopulator<String[]>> cellItem, String componentId, IModel<String[]> rowModel) {
+            String value = rowModel.getObject()[index];
+            if (value.matches("https?://.+")) {
+                cellItem.add(new NanodashLink(componentId, value));
+            } else {
+                cellItem.add(new Label(componentId, value));
+            }
+        }
+
+    }
+
+}
diff --git a/src/main/java/com/knowledgepixels/nanodash/component/RdfResultComponent.java b/src/main/java/com/knowledgepixels/nanodash/component/RdfResultComponent.java
new file mode 100644
index 00000000..d6ca99b5
--- /dev/null
+++ b/src/main/java/com/knowledgepixels/nanodash/component/RdfResultComponent.java
@@ -0,0 +1,65 @@
+package com.knowledgepixels.nanodash.component;
+
+import com.knowledgepixels.nanodash.ApiCache;
+import org.apache.wicket.Component;
+import org.apache.wicket.markup.html.basic.Label;
+import org.eclipse.rdf4j.model.Model;
+import org.nanopub.extra.services.QueryRef;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * A component that asynchronously loads and displays the RDF result of a CONSTRUCT query.
+ */
+public abstract class RdfResultComponent extends ResultComponent {
+
+    private final QueryRef queryRef;
+    private Model model = null;
+    private static final Logger logger = LoggerFactory.getLogger(RdfResultComponent.class);
+
+    /**
+     * Constructor.
+     *
+     * @param id       the component id
+     * @param queryRef the QueryRef for the CONSTRUCT query
+     */
+    public RdfResultComponent(String id, QueryRef queryRef) {
+        super(id);
+        this.queryRef = queryRef;
+    }
+
+    @Override
+    public Component getLazyLoadComponent(String markupId) {
+        while (true) {
+            if (!ApiCache.isRunning(queryRef)) {
+                try {
+                    model = ApiCache.retrieveRdfModelAsync(queryRef);
+                    if (model != null) break;
+                } catch (Exception ex) {
+                    return new Label(markupId, "<span class=\"negative\">API call failed.</span>").setEscapeModelStrings(false);
+                }
+            }
+            try {
+                Thread.sleep(100);
+            } catch (InterruptedException ex) {
+                logger.error("Interrupted while waiting for RDF response", ex);
+            }
+        }
+        return getRdfResultComponent(markupId, model);
+    }
+
+    @Override
+    protected boolean isContentReady() {
+        return model != null || !ApiCache.isRunning(queryRef);
+    }
+
+    /**
+     * Implement to return the component that displays the RDF result.
+     *
+     * @param markupId the markup ID for the component
+     * @param model    the RDF model from the CONSTRUCT query
+     * @return a Component that displays the RDF model
+     */
+    public abstract Component getRdfResultComponent(String markupId, Model model);
+
+}
diff --git a/src/main/java/com/knowledgepixels/nanodash/page/QueryPage.java b/src/main/java/com/knowledgepixels/nanodash/page/QueryPage.java
index f3fd2753..525f5172 100644
--- a/src/main/java/com/knowledgepixels/nanodash/page/QueryPage.java
+++ b/src/main/java/com/knowledgepixels/nanodash/page/QueryPage.java
@@ -3,12 +3,17 @@
 import com.github.jsonldjava.shaded.com.google.common.base.Charsets;
 import com.google.common.collect.ArrayListMultimap;
 import com.google.common.collect.Multimap;
+import com.knowledgepixels.nanodash.ApiCache;
 import com.knowledgepixels.nanodash.GrlcQuery;
 import com.knowledgepixels.nanodash.Utils;
 import com.knowledgepixels.nanodash.ViewDisplay;
 import com.knowledgepixels.nanodash.component.QueryParamField;
+import com.knowledgepixels.nanodash.component.QueryResultRdf;
 import com.knowledgepixels.nanodash.component.QueryResultTableBuilder;
+import com.knowledgepixels.nanodash.component.RdfResultComponent;
 import com.knowledgepixels.nanodash.component.TitleBar;
+import org.apache.wicket.Component;
+import org.eclipse.rdf4j.model.Model;
 import org.apache.wicket.RestartResponseException;
 import org.apache.wicket.feedback.FeedbackMessage;
 import org.apache.wicket.markup.html.WebMarkupContainer;
@@ -174,6 +179,19 @@ public void onSubmit() {
 
         if (queryId == null) {
             add(new Label("resulttable").setVisible(false));
+        } else if (q.isConstructQuery()) {
+            QueryRef constructQueryRef = new QueryRef(queryId, queryParams);
+            Model rdfModel = ApiCache.retrieveRdfModelAsync(constructQueryRef);
+            if (rdfModel != null) {
+                add(new QueryResultRdf("resulttable", rdfModel));
+            } else {
+                add(new RdfResultComponent("resulttable", constructQueryRef) {
+                    @Override
+                    public Component getRdfResultComponent(String markupId, Model model) {
+                        return new QueryResultRdf(markupId, model);
+                    }
+                });
+            }
         } else {
             add(QueryResultTableBuilder.create("resulttable", new QueryRef(queryId, queryParams), new ViewDisplay(20)).plain(true).build());
         }