feat: prevent draft creation for unchanged dataset metadata

src/main/java/edu/harvard/iq/dataverse/api/Datasets.java

@@ -849,7 +849,12 @@ public Response updateDraftVersion(@Context ContainerRequestContext crc, String
                 return error( Response.Status.BAD_REQUEST, "You may not add files via this api.");
             }
 
-            boolean updateDraft = ds.getLatestVersion().isDraft();
+            DatasetVersion latestVersion = ds.getLatestVersion();
+            if (isDatasetVersionNoOp(incomingVersion, latestVersion)) {
+                return ok(json(latestVersion, true));
+            }
+
+            boolean updateDraft = latestVersion.isDraft();
 
             DatasetVersion managedVersion;
             if (updateDraft) {
@@ -882,6 +887,12 @@ public Response updateDraftVersion(@Context ContainerRequestContext crc, String
         }
     }
 
+    // Helper extracted to make no-op detection testable.
+    static boolean isDatasetVersionNoOp(DatasetVersion incomingVersion, DatasetVersion latestVersion) {
+        DatasetVersionDifference diff = new DatasetVersionDifference(incomingVersion, latestVersion);
+        return diff.getDetailDataByBlock().isEmpty() && diff.getChangedTermsAccess().isEmpty();
+    }
+
     @GET
     @AuthRequired
     @Path("{id}/versions/{versionId}/metadata")

src/test/java/edu/harvard/iq/dataverse/api/DatasetsIT.java

@@ -7540,6 +7540,66 @@ public void testGetDatasetWithTermsOfUseAndGuestbook() throws IOException, JsonP
                 .body("data.guestbookId", equalTo(guestbook.getId().intValue()));
     }
 
+    @Test
+    public void testUpdateDatasetMetadataNoOp() {
+        String apiToken = getSuperuserToken();
+        String collectionAlias = UtilIT.createRandomCollectionGetAlias(apiToken);
+        UtilIT.publishDataverseViaNativeApi(collectionAlias, apiToken)
+                .then().assertThat().statusCode(OK.getStatusCode());
+
+        String updateJsonFile = "doc/sphinx-guides/source/_static/api/dataset-update-metadata.json";
+
+        // 1. Create a dataset and update it with known metadata from a file
+        Response createDataset = UtilIT.createRandomDatasetViaNativeApi(collectionAlias, apiToken);
+        createDataset.then().assertThat().statusCode(CREATED.getStatusCode());
+        Integer datasetId = UtilIT.getDatasetIdFromResponse(createDataset);
+        String datasetPid = UtilIT.getDatasetPersistentIdFromResponse(createDataset);
+
+        UtilIT.updateDatasetMetadataViaNative(datasetPid, updateJsonFile, apiToken)
+                .then().assertThat().statusCode(OK.getStatusCode());
+        UtilIT.publishDatasetViaNativeApi(datasetId, "major", apiToken)
+                .then().assertThat().statusCode(OK.getStatusCode());
+        UtilIT.getDatasetVersion(datasetPid, DS_VERSION_DRAFT, apiToken)
+                .then().assertThat().statusCode(NOT_FOUND.getStatusCode());
+
+        // 2. Call API with identical metadata (Published case)
+        UtilIT.updateDatasetMetadataViaNative(datasetPid, updateJsonFile, apiToken)
+                .then().assertThat().statusCode(OK.getStatusCode());
+
+        // 3. Verify no draft was created
+        UtilIT.getDatasetVersion(datasetPid, DS_VERSION_DRAFT, apiToken)
+                .then().assertThat().statusCode(NOT_FOUND.getStatusCode());
+
+        // 4. Test the scenario where a draft ALREADY exists
+        String currentMetadata = UtilIT.getDatasetJson(updateJsonFile);
+        String draftJson = currentMetadata.replace("\"newTitle\"", "\"Updated Title\"");
+
+        given()
+                .header(API_TOKEN_HTTP_HEADER, apiToken)
+                .body(draftJson)
+                .contentType("application/json")
+                .put("/api/datasets/:persistentId/versions/" + DS_VERSION_DRAFT + "?persistentId=" + datasetPid)
+                .then().assertThat().statusCode(OK.getStatusCode());
+
+        Response draftResponse = UtilIT.getDatasetVersion(datasetPid, DS_VERSION_DRAFT, apiToken);
+        draftResponse.then().assertThat().statusCode(OK.getStatusCode());
+        String lastUpdateTimeBefore = draftResponse.jsonPath().getString("data.lastUpdateTime");
+
+        // 5. Call API with identical metadata to the current draft
+        given()
+                .header(API_TOKEN_HTTP_HEADER, apiToken)
+                .body(draftJson)
+                .contentType("application/json")
+                .put("/api/datasets/:persistentId/versions/" + DS_VERSION_DRAFT + "?persistentId=" + datasetPid)
+                .then().assertThat().statusCode(OK.getStatusCode());
+
+        // 6. Verify it was a no-op (lastUpdateTime should NOT have changed)
+        Response draftResponseAfter = UtilIT.getDatasetVersion(datasetPid, DS_VERSION_DRAFT, apiToken);
+        String lastUpdateTimeAfter = draftResponseAfter.jsonPath().getString("data.lastUpdateTime");
+
+        assertEquals(lastUpdateTimeBefore, lastUpdateTimeAfter, "Last update time should not change for no-op metadata update on draft");
+    }
+
     private String getSuperuserToken() {
         Response createResponse = UtilIT.createRandomUser();
         String adminApiToken = UtilIT.getApiTokenFromResponse(createResponse);

src/test/java/edu/harvard/iq/dataverse/api/DatasetsTest.java

@@ -3,17 +3,44 @@
 import edu.harvard.iq.dataverse.Dataset;
 import edu.harvard.iq.dataverse.GlobalId;
 import edu.harvard.iq.dataverse.pidproviders.doi.AbstractDOIProvider;
+import edu.harvard.iq.dataverse.*;
 import org.junit.jupiter.api.Test;
+
 import java.util.HashSet;
+import java.util.List;
 import java.util.Set;
 import java.util.function.Predicate;
 import java.util.stream.Collectors;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertFalse;
 
 public class DatasetsTest {
 
+    @Test
+    public void testIsDatasetVersionNoOp() {
+        DatasetVersion incoming = emptyVersion();
+        DatasetVersion latest = emptyVersion();
+        assertTrue(Datasets.isDatasetVersionNoOp(incoming, latest));
+
+        DatasetField field = new DatasetField();
+        DatasetFieldType type = new DatasetFieldType();
+        type.setName("title");
+        type.setChildDatasetFieldTypes(List.of());
+        field.setDatasetFieldType(type);
+        field.setDatasetFieldValues(List.of(new DatasetFieldValue(field, "Changed title")));
+        incoming.setDatasetFields(List.of(field));
+
+        assertFalse(Datasets.isDatasetVersionNoOp(incoming, latest));
+    }
+
+    private static DatasetVersion emptyVersion() {
+        DatasetVersion v = new DatasetVersion();
+        v.setTermsOfUseAndAccess(new TermsOfUseAndAccess());
+        return v;
+    }
+
     /**
      * Test cleanup filter
      */