feat: add implicit ordering for startAt(DocumentReference) calls (#417)

Author: schmidt-sebastian

google-cloud-firestore/src/main/java/com/google/cloud/firestore/Query.java

@@ -988,9 +988,14 @@ public Query startAt(@Nonnull DocumentSnapshot snapshot) {
    */
   @Nonnull
   public Query startAt(Object... fieldValues) {
-    Cursor cursor = createCursor(options.getFieldOrders(), fieldValues, true);
+    ImmutableList<FieldOrder> fieldOrders =
+        fieldValues.length == 1 && fieldValues[0] instanceof DocumentReference
+            ? createImplicitOrderBy()
+            : options.getFieldOrders();
+    Cursor cursor = createCursor(fieldOrders, fieldValues, true);
 
     Builder newOptions = options.toBuilder();
+    newOptions.setFieldOrders(fieldOrders);
     newOptions.setStartCursor(cursor);
     return new Query(rpcContext, newOptions.build());
   }
@@ -1069,9 +1074,14 @@ public Query startAfter(@Nonnull DocumentSnapshot snapshot) {
    * @return The created Query.
    */
   public Query startAfter(Object... fieldValues) {
-    Cursor cursor = createCursor(options.getFieldOrders(), fieldValues, false);
+    ImmutableList<FieldOrder> fieldOrders =
+        fieldValues.length == 1 && fieldValues[0] instanceof DocumentReference
+            ? createImplicitOrderBy()
+            : options.getFieldOrders();
+    Cursor cursor = createCursor(fieldOrders, fieldValues, false);
 
     Builder newOptions = options.toBuilder();
+    newOptions.setFieldOrders(fieldOrders);
     newOptions.setStartCursor(cursor);
     return new Query(rpcContext, newOptions.build());
   }
@@ -1105,9 +1115,14 @@ public Query endBefore(@Nonnull DocumentSnapshot snapshot) {
    */
   @Nonnull
   public Query endBefore(Object... fieldValues) {
-    Cursor cursor = createCursor(options.getFieldOrders(), fieldValues, true);
+    ImmutableList<FieldOrder> fieldOrders =
+        fieldValues.length == 1 && fieldValues[0] instanceof DocumentReference
+            ? createImplicitOrderBy()
+            : options.getFieldOrders();
+    Cursor cursor = createCursor(fieldOrders, fieldValues, true);
 
     Builder newOptions = options.toBuilder();
+    newOptions.setFieldOrders(fieldOrders);
     newOptions.setEndCursor(cursor);
     return new Query(rpcContext, newOptions.build());
   }
@@ -1121,9 +1136,14 @@ public Query endBefore(Object... fieldValues) {
    */
   @Nonnull
   public Query endAt(Object... fieldValues) {
-    Cursor cursor = createCursor(options.getFieldOrders(), fieldValues, false);
+    ImmutableList<FieldOrder> fieldOrders =
+        fieldValues.length == 1 && fieldValues[0] instanceof DocumentReference
+            ? createImplicitOrderBy()
+            : options.getFieldOrders();
+    Cursor cursor = createCursor(fieldOrders, fieldValues, false);
 
     Builder newOptions = options.toBuilder();
+    newOptions.setFieldOrders(fieldOrders);
     newOptions.setEndCursor(cursor);
     return new Query(rpcContext, newOptions.build());
   }

google-cloud-firestore/src/test/java/com/google/cloud/firestore/QueryTest.java

@@ -18,6 +18,7 @@
 
 import static com.google.cloud.firestore.LocalFirestoreHelper.COLLECTION_ID;
 import static com.google.cloud.firestore.LocalFirestoreHelper.DOCUMENT_NAME;
+import static com.google.cloud.firestore.LocalFirestoreHelper.DOCUMENT_PATH;
 import static com.google.cloud.firestore.LocalFirestoreHelper.SINGLE_FIELD_SNAPSHOT;
 import static com.google.cloud.firestore.LocalFirestoreHelper.endAt;
 import static com.google.cloud.firestore.LocalFirestoreHelper.filter;
@@ -598,6 +599,26 @@ public void withDocumentIdAndDocumentSnapshotCursor() {
     assertEquals(queryRequest, runQuery.getValue());
   }
 
+  @Test
+  public void withDocumentReferenceCursor() {
+    doAnswer(queryResponse())
+        .when(firestoreMock)
+        .streamRequest(
+            runQuery.capture(),
+            streamObserverCapture.capture(),
+            Matchers.<ServerStreamingCallable>any());
+
+    DocumentReference documentCursor = firestoreMock.document(DOCUMENT_PATH);
+    Value documentValue = reference(DOCUMENT_NAME);
+
+    query.startAt(documentCursor).get();
+
+    RunQueryRequest queryRequest =
+        query(order("__name__", StructuredQuery.Direction.ASCENDING), startAt(documentValue, true));
+
+    assertEquals(queryRequest, runQuery.getValue());
+  }
+
   @Test
   public void withExtractedDirectionForDocumentSnapshotCursor() {
     doAnswer(queryResponse())

google-cloud-firestore/src/test/java/com/google/cloud/firestore/it/ITSystemTest.java

@@ -554,6 +554,20 @@ public void startAfter() throws Exception {
     assertEquals(2L, querySnapshot.getDocuments().get(0).get("foo"));
   }
 
+  @Test
+  public void startAfterAddsAnImplicitOrderByForDocumentReferences() throws Exception {
+    DocumentReference doc1 = randomColl.document("doc1");
+    DocumentReference doc2 = randomColl.document("doc2");
+
+    doc1.set(map("foo", 1)).get();
+    doc2.set(map("foo", 1)).get();
+
+    QuerySnapshot querySnapshot = randomColl.startAfter(doc1).get().get();
+    assertEquals(1, querySnapshot.size());
+    Iterator<QueryDocumentSnapshot> documents = querySnapshot.iterator();
+    assertEquals(doc2, documents.next().getReference());
+  }
+
   @Test
   public void endAt() throws Exception {
     addDocument("foo", 1);