Fix No notification for write transaction that contains only change t…

…o backlink property (#6074) * notify backlink object in case of modifications * entry in the changelog * Update test/object-store/object.cpp Co-authored-by: James Stone <[email protected]> * code review * adding some more testing * code review Co-authored-by: James Stone <[email protected]>
realm · Dec 5, 2022 · a4fafc1 · a4fafc1
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -7,6 +7,7 @@
 ### Fixed
 * <How do the end-user experience this issue? what was the impact?> ([#????](https://github.com/realm/realm-core/issues/????), since v?.?.?)
 * Fixed `realm_add_realm_refresh_callback` and notify immediately that there is not transaction snapshot to advance to. ([#6075](https://github.com/realm/realm-core/issues/6075), since v12.6.0)
+* Fix no notification for write transaction that contains only change to backlink property. ([#4994](https://github.com/realm/realm-core/issues/4994), since v11.4.1)
 
 ### Breaking changes
 * FLX Subscription API reworked to better match SDK consumption patterns ([#6065](https://github.com/realm/realm-core/pull/6065)). Not all changes are breaking, but listing them all here together.

diff --git a/src/realm/object-store/impl/deep_change_checker.cpp b/src/realm/object-store/impl/deep_change_checker.cpp
@@ -397,7 +397,11 @@ void CollectionKeyPathChangeChecker::find_changed_columns(std::vector<ColKey>& c
         auto last_column_key = last_key_path_element.second;
         if (last_column_key.get_type() == col_type_BackLink) {
             auto iterator = m_info.tables.find(table.get_key());
-            if (iterator != m_info.tables.end() && !iterator->second.insertions_empty()) {
+            auto table_has_changed = [iterator] {
+                return !iterator->second.insertions_empty() || !iterator->second.modifications_empty() ||
+                       !iterator->second.deletions_empty();
+            };
+            if (iterator != m_info.tables.end() && table_has_changed()) {
                 ColKey root_column_key = key_path[0].second;
                 changed_columns.push_back(root_column_key);
             }

diff --git a/test/object-store/object.cpp b/test/object-store/object.cpp
@@ -914,6 +914,38 @@ TEST_CASE("object") {
                         REQUIRE(change.columns.size() == 1);
                         REQUIRE_INDICES(change.columns[col_target_backlink.value], 0);
                     }
+                    SECTION("changes to backlink are reported both to origin and destination object") {
+                        Object object_origin2;
+                        write([&] {
+                            Obj obj_origin2 = table_origin->create_object_with_primary_key(300);
+                            object_origin2 = Object{r, obj_origin2};
+                        });
+
+                        // add a backlink
+                        auto token_with_backlink = require_change(object_target, key_path_array_target_backlink);
+                        write([&] {
+                            object_origin2.set_property_value(d, "link", util::Any(object_target));
+                        });
+                        REQUIRE_INDICES(change.modifications, 0);
+                        REQUIRE(change.columns.size() == 1);
+                        REQUIRE_INDICES(change.columns[col_target_backlink.value], 0);
+
+                        // nullify a backlink
+                        write([&] {
+                            object_origin2.set_property_value(d, "link", std::any());
+                        });
+                        REQUIRE_INDICES(change.modifications, 0);
+                        REQUIRE(change.columns.size() == 1);
+                        REQUIRE_INDICES(change.columns[col_target_backlink.value], 0);
+
+                        // remove a backlink
+                        write([&] {
+                            table_origin->remove_object(object_origin2.obj().get_key());
+                        });
+                        REQUIRE_INDICES(change.modifications, 0);
+                        REQUIRE(change.columns.size() == 1);
+                        REQUIRE_INDICES(change.columns[col_target_backlink.value], 0);
+                    }
                 }
             }