perf: perform matching over indices

src/N3Store.js

@@ -1026,6 +1026,31 @@ export default class N3Store {
   }
 }
 
+/**
+ * Returns a subset of the `index` with that part of the index
+ * matching the `ids` array. `ids` contains 3 elements that are
+ * either numerical ids; or `null`.
+ *
+ * `false` is returned when there are no matching indices; this should
+ * *not* be set as the value for an index.
+ */
+function indexMatch(index, ids, depth = 0) {
+  const ind = ids[depth];
+  if (ind && !(ind in index))
+    return false;
+
+  let target = false;
+  for (const key in (ind ? { [ind]: index[ind] } : index)) {
+    const result = depth === 2 ? null : indexMatch(index[key], ids, depth + 1);
+
+    if (result !== false) {
+      target = target || Object.create(null);
+      target[key] = result;
+    }
+  }
+  return target;
+}
+
 /**
  * A class that implements both DatasetCore and Readable.
  */
@@ -1039,8 +1064,27 @@ class DatasetCoreAndReadableStream extends Readable {
     if (!this._filtered) {
       const { n3Store, graph, object, predicate, subject } = this;
       const newStore = this._filtered = new N3Store({ factory: n3Store._factory, entityIndex: this.options.entityIndex });
-      for (const quad of n3Store.readQuads(subject, predicate, object, graph))
-        newStore.addQuad(quad);
+      const graphs = n3Store._getGraphs(graph);
+
+      let subjectId, predicateId, objectId;
+
+      // Translate IRIs to internal index keys.
+      if (subject   && !(subjectId   = newStore._termToNumericId(subject))   ||
+          predicate && !(predicateId = newStore._termToNumericId(predicate)) ||
+          object    && !(objectId    = newStore._termToNumericId(object)))
+        return newStore;
+
+      for (const graph in graphs) {
+        const subjects = indexMatch(graphs[graph].subjects, [subjectId, predicateId, objectId]);
+        if (subjects) {
+          newStore._graphs[graph] = {
+            subjects,
+            predicates: indexMatch(graphs[graph].predicates, [predicateId, objectId, subjectId]),
+            objects: indexMatch(graphs[graph].objects, [objectId, subjectId, predicateId]),
+          };
+        }
+      }
+      newStore._size = null;
     }
     return this._filtered;
   }

test/N3Store-test.js

@@ -2,6 +2,7 @@ import {
   Store,
   termFromId, termToId,
   EntityIndex,
+  DataFactory,
 } from '../src';
 import {
   NamedNode,
@@ -13,6 +14,8 @@ import namespaces from '../src/IRIs';
 import { Readable } from 'readable-stream';
 import { arrayifyStream } from 'arrayify-stream';
 
+const { namedNode } = DataFactory;
+
 describe('Store', () => {
   describe('The Store export', () => {
     it('should be a function', () => {
@@ -695,6 +698,14 @@ describe('Store', () => {
 
           expect(nextDataset.has(new Quad('s2', 'p1', 'o1'))).toBe(true);
           expect(nextDataset.has(new Quad('s2', 'p2', 'o2'))).toBe(true);
+          expect(nextDataset.match(namedNode('s2'), null, null).has(new Quad('s2', 'p2', 'o2'))).toBe(true);
+          expect(nextDataset.match(null, namedNode('p2'), null).has(new Quad('s2', 'p2', 'o2'))).toBe(true);
+          expect(nextDataset.match(null, null, namedNode('o2')).has(new Quad('s2', 'p2', 'o2'))).toBe(true);
+          expect(nextDataset.size).toBe(2);
+          nextDataset.add(new Quad('s2', 'p1', 'onew'));
+          expect(nextDataset.size).toBe(3);
+          nextDataset.add(new Quad('s2', 'p1', 'onew'));
+          expect(nextDataset.size).toBe(3);
 
           nextDataset.delete(new Quad('s2', 'p1', 'o1'));
           nextDataset.delete(new Quad('s2', 'p2', 'o2'));