fix(node): give every element of a struct-built array its own id

code/+openminds/Node.m

@@ -120,6 +120,14 @@
             else
                 if ~isscalar(instance) % Preallocate object array
                     obj(1, numel(instance)) = feval( class(obj) );
+                    % Growing the array fills the elements in between with
+                    % copies of one default object, so those copies share
+                    % the id that object generated. Every element gets its
+                    % own blank node id here; fromStruct replaces it when
+                    % the struct carries an identifier.
+                    for i = 1:numel(obj)
+                        obj(i).id = obj(i).generateInstanceId();
+                    end
                 end
                 for i = 1:numel( instance )
                     % Todo: Separate method to handle reference structure.

tools/tests/unitTests/CollectionTest.m

@@ -269,6 +269,36 @@ function testSaveAndLoad(testCase)
             testCase.verifyTrue(newCollection.isKey(org.id));
         end
 
+        function testEmbeddedArrayOfFourSurvivesRoundTrip(testCase)
+        % A multi-valued embedded property is saved without identifiers
+        % and read back as a struct array. Each value must come back as a
+        % node of its own, or the owning node fails the uniqueness check
+        % on that property and is dropped from the loaded collection. Four
+        % values, so that the array holds more than one element between
+        % the first and the last.
+
+            hashes = openminds.core.data.Hash.empty;
+            for digest = ["1", "2", "3", "4"]
+                hashes(end+1) = openminds.core.data.Hash( ...
+                    "algorithm", "SHA-1", "digest", digest); %#ok<AGROW>
+            end
+            file = openminds.core.data.File("name", "data.bin", ...
+                "IRI", "https://example.org/data.bin", "hash", hashes);
+
+            filePath = 'embedded-array.jsonld';
+            openminds.Collection(file).save(filePath);
+            reloaded = openminds.Collection(filePath);
+
+            testCase.assertTrue(reloaded.isKey(file.id), ...
+                'The node holding the embedded values was dropped on load.')
+            reloadedFile = reloaded.get(file.id);
+            testCase.assertNumElements(reloadedFile.hash, 4)
+            identifiers = arrayfun(@(h) string(h.id), reloadedFile.hash);
+            testCase.verifyEqual(numel(unique(identifiers)), 4, ...
+                'The embedded values share an identifier after loading.')
+            testCase.verifyEqual([reloadedFile.hash.digest], ["1", "2", "3", "4"])
+        end
+
         function testSaveWithMetadataStoreOption(testCase)
         % A store passed to save by name-value must be the store used.
         % This went through obj.MetadataStore instead, which is empty

tools/tests/unitTests/InstanceTest.m

@@ -98,5 +98,26 @@ function testSaveLoadForTypedInstance(testCase, MetadataType)
             testCase.verifyEqual(S.itemPreSave, itemPreSave, ...
                 sprintf('Loaded object does not match the original for %s', metadataType.ClassName));
         end
+
+        function testStructArrayWithoutIdsGetsDistinctIds(testCase)
+        % A multi-valued embedded property is read as a struct array with
+        % no identifiers, and each element must become a node of its own.
+        % Four elements, so that the array holds more than one element
+        % between the first and the last.
+
+            structs = struct( ...
+                'algorithm', {"SHA-1", "SHA-1", "SHA-1", "SHA-1"}, ...
+                'digest', {"1", "2", "3", "4"});
+
+            hashes = openminds.core.data.Hash(structs);
+
+            testCase.assertNumElements(hashes, 4)
+            identifiers = arrayfun(@(h) string(h.id), hashes);
+            testCase.verifyEqual(numel(unique(identifiers)), 4, ...
+                'Elements built from one struct array share an identifier.')
+            testCase.verifyTrue(all(startsWith(identifiers, "_:")), ...
+                'An element whose struct carries no identifier gets a blank node id.')
+            testCase.verifyEqual([hashes.digest], ["1", "2", "3", "4"])
+        end
     end
 end