fix: Adding skolemize to the SparqlHandler (#265)

* Adding skolemize to the SparqlHandler

* Adding a test to check if the skolemized node is used inside the query

* Adding regression test for skolemization in mutations

src/SparqlHandler.js

@@ -60,7 +60,7 @@ export default class SparqlHandler {
     let subject, where;
     // If the only condition is a subject, we need no WHERE clause
     if (conditions.length === 1) {
-      subject = this.termToString(conditions[0].subject);
+      subject = this.termToString(skolemize(conditions[0].subject));
       where = [];
     }
     // Otherwise, create a WHERE clause from all conditions
@@ -76,7 +76,7 @@ export default class SparqlHandler {
     for (const { predicate, reverse, objects } of predicateObjects) {
       // Mutate either only the specified objects, or all of them
       const objectStrings = objects ?
-        objects.map(o => this.termToString(o)) :
+        objects.map(o => this.termToString(skolemize(o))) :
         [this.createVar(predicate.value, scope)];
       // Generate a triple pattern for all subjects
       mutations.push(...this.triplePatterns(subject, predicate, objectStrings, reverse));

test/integration/mutation-expressions-test.js

@@ -2,10 +2,11 @@ import PathProxy from '../../src/PathProxy';
 import PathExpressionHandler from '../../src/PathExpressionHandler';
 import InsertFunctionHandler from '../../src/InsertFunctionHandler';
 import DeleteFunctionHandler from '../../src/DeleteFunctionHandler';
+import SparqlHandler from '../../src/SparqlHandler';
 import MutationExpressionsHandler from '../../src/MutationExpressionsHandler';
 import JSONLDResolver from '../../src/JSONLDResolver';
 import context from '../context';
-import { namedNode, literal } from '@rdfjs/data-model';
+import { namedNode, literal, blankNode } from '@rdfjs/data-model';
 
 describe('a query path with a path expression handler', () => {
   const handlers = {
@@ -224,4 +225,23 @@ describe('a query path with a path expression handler', () => {
       },
     ]);
   });
+
+  it('skolemizes blank nodes inside mutationExpressions', async () => {
+    const handler = new SparqlHandler();
+    const mutationExpressions = [
+      {
+        mutationType: 'INSERT',
+        conditions: [{ subject: blankNode('a') }],
+        predicateObjects: [{
+          predicate: namedNode('https://example.org/p'),
+          objects: [blankNode('b')],
+        }],
+      },
+    ];
+
+    const query = await handler.handle({}, { mutationExpressions });
+
+    expect(query).toContain('urn:ldflex:sk0');
+    expect(query).toContain('urn:ldflex:sk1');
+  });
 });