RCORE-2108: Clear backlinks when object containing nested collections is deleted (#7680)

Author: jedelbo

CHANGELOG.md

@@ -30,6 +30,7 @@
 ### Fixed
 * Fixed a bug when running a IN query on a String/Int/UUID/ObjectId property that was indexed. ([7642](https://github.com/realm/realm-core/issues/7642) since v14.6.0)
 * Fixed a bug when running a IN query on a integer property where double/float parameters were ignored. ([7642](https://github.com/realm/realm-core/issues/7642) since v14.6.0)
+* Having links in a nested collections would leave the file inconsistent if the top object is removed. ([#7657](https://github.com/realm/realm-core/issues/7657), since 14.0.0)
 
 ### Breaking changes
 * None.

src/realm/array_backlink.cpp

@@ -220,7 +220,20 @@ void ArrayBacklink::verify() const
                     REALM_ASSERT(src_obj.get_collection_ptr(src_col_key)->find_any(target_link) != npos);
                 }
                 else {
-                    REALM_ASSERT(src_obj.get<Mixed>(src_col_key).get_link() == target_link);
+                    auto val = src_obj.get<Mixed>(src_col_key);
+                    if (val.is_type(type_TypedLink)) {
+                        REALM_ASSERT(src_obj.get<Mixed>(src_col_key).get_link() == target_link);
+                    }
+                    else if (val.is_type(type_List)) {
+                        DummyParent parent(src_table, val.get_ref());
+                        Lst<Mixed> list(parent, 0);
+                        REALM_ASSERT(list.find_any(target_link) != npos);
+                    }
+                    else if (val.is_type(type_Dictionary)) {
+                        DummyParent parent(src_table, val.get_ref());
+                        Dictionary dict(parent, 0);
+                        REALM_ASSERT(dict.find_any(target_link) != npos);
+                    }
                 }
                 continue;
             }

src/realm/cluster.cpp

@@ -761,24 +761,48 @@ inline void Cluster::do_erase(size_t ndx, ColKey col_key)
     values.set_parent(this, col_ndx.val + s_first_col_index);
     set_spec<T>(values, col_ndx);
     values.init_from_parent();
-    ObjLink link;
     if constexpr (std::is_same_v<T, ArrayTypedLink>) {
-        link = values.get(ndx);
-    }
-    if constexpr (std::is_same_v<T, ArrayMixed>) {
-        Mixed value = values.get(ndx);
-        if (value.is_type(type_TypedLink)) {
-            link = value.get<ObjLink>();
+        if (ObjLink link = values.get(ndx)) {
+            if (const Table* origin_table = m_tree_top.get_owning_table()) {
+                auto target_obj = origin_table->get_parent_group()->get_object(link);
+
+                ColKey backlink_col_key =
+                    target_obj.get_table()->find_backlink_column(col_key, origin_table->get_key());
+                REALM_ASSERT(backlink_col_key);
+                target_obj.remove_one_backlink(backlink_col_key, get_real_key(ndx)); // Throws
+            }
         }
     }
-    if (link) {
-        if (const Table* origin_table = m_tree_top.get_owning_table()) {
-            auto target_obj = origin_table->get_parent_group()->get_object(link);
+    values.erase(ndx);
+}
 
-            ColKey backlink_col_key = target_obj.get_table()->find_backlink_column(col_key, origin_table->get_key());
-            REALM_ASSERT(backlink_col_key);
-            target_obj.remove_one_backlink(backlink_col_key, get_real_key(ndx)); // Throws
-        }
+inline void Cluster::do_erase_mixed(size_t ndx, ColKey col_key, ObjKey key, CascadeState& state)
+{
+    const Table* origin_table = m_tree_top.get_owning_table();
+    auto col_ndx = col_key.get_index();
+
+    ArrayMixed values(m_alloc);
+    values.set_parent(this, col_ndx.val + s_first_col_index);
+    values.init_from_parent();
+
+    Mixed value = values.get(ndx);
+    if (value.is_type(type_TypedLink)) {
+        ObjLink link = value.get<ObjLink>();
+        auto target_obj = origin_table->get_parent_group()->get_object(link);
+
+        ColKey backlink_col_key = target_obj.get_table()->find_backlink_column(col_key, origin_table->get_key());
+        REALM_ASSERT(backlink_col_key);
+        target_obj.remove_one_backlink(backlink_col_key, get_real_key(ndx)); // Throws
+    }
+    if (value.is_type(type_List)) {
+        Obj obj(origin_table->m_own_ref, get_mem(), key, ndx);
+        Lst<Mixed> list(obj, col_key);
+        list.remove_backlinks(state);
+    }
+    if (value.is_type(type_Dictionary)) {
+        Obj obj(origin_table->m_own_ref, get_mem(), key, ndx);
+        Dictionary dict(obj, col_key);
+        dict.remove_backlinks(state);
     }
     values.erase(ndx);
 }
@@ -897,7 +921,7 @@ size_t Cluster::erase(ObjKey key, CascadeState& state)
                 do_erase<ArrayBinary>(ndx, col_key);
                 break;
             case col_type_Mixed:
-                do_erase<ArrayMixed>(ndx, col_key);
+                do_erase_mixed(ndx, col_key, key, state);
                 break;
             case col_type_Timestamp:
                 do_erase<ArrayTimestamp>(ndx, col_key);

src/realm/cluster.hpp

@@ -349,6 +349,7 @@ class Cluster : public ClusterNode {
         remove_backlinks(get_owning_table(), origin_key, col, links, state);
     }
     void do_erase_key(size_t ndx, ColKey col, CascadeState& state);
+    void do_erase_mixed(size_t ndx, ColKey col, ObjKey key, CascadeState& state);
     void do_insert_key(size_t ndx, ColKey col, Mixed init_val, ObjKey origin_key);
     void do_insert_link(size_t ndx, ColKey col, Mixed init_val, ObjKey origin_key);
     void do_insert_mixed(size_t ndx, ColKey col_key, Mixed init_value, ObjKey origin_key);

src/realm/replication.cpp

@@ -199,6 +199,7 @@ void Replication::select_obj(ObjKey key)
         }
     }
     m_selected_obj = key;
+    m_selected_list = CollectionId();
 }
 
 void Replication::do_set(const Table* t, ColKey col_key, ObjKey key, _impl::Instruction variant)

src/realm/replication.hpp

@@ -363,6 +363,13 @@ class Replication {
         return m_logger;
     }
 
+    util::Logger* would_log(util::Logger::Level level) const noexcept
+    {
+        if (m_logger && m_logger->would_log(level))
+            return m_logger;
+        return nullptr;
+    }
+
 protected:
     Replication() = default;
 
@@ -439,13 +446,6 @@ class Replication {
                                   Mixed index) const;
     Path get_prop_name(Path&&) const;
     size_t transact_log_size();
-
-    util::Logger* would_log(util::Logger::Level level) const noexcept
-    {
-        if (m_logger && m_logger->would_log(level))
-            return m_logger;
-        return nullptr;
-    }
 };
 
 class Replication::Interrupted : public std::exception {

src/realm/table.cpp

@@ -2367,6 +2367,13 @@ Obj Table::create_object_with_primary_key(const Mixed& primary_key, FieldValues&
 
     // Check if unresolved exists
     if (unres_key) {
+        if (Replication* repl = get_repl()) {
+            if (auto logger = repl->would_log(util::Logger::Level::debug)) {
+                logger->log(LogCategory::object, util::Logger::Level::debug, "Cancel tombstone on '%1': %2",
+                            get_class_name(), unres_key);
+            }
+        }
+
         auto tombstone = m_tombstones->get(unres_key);
         ret.assign_pk_and_backlinks(tombstone);
         // If tombstones had no links to it, it may still be alive
@@ -2638,6 +2645,13 @@ Obj Table::get_or_create_tombstone(ObjKey key, ColKey pk_col, Mixed pk_val)
         }
         return tombstone;
     }
+    if (Replication* repl = get_repl()) {
+        if (auto logger = repl->would_log(util::Logger::Level::debug)) {
+            logger->log(LogCategory::object, util::Logger::Level::debug,
+                        "Create tombstone for object '%1' with primary key %2 : %3", get_class_name(), pk_val,
+                        unres_key);
+        }
+    }
     return m_tombstones->insert(unres_key, {{pk_col, pk_val}});
 }
 

test/test_list.cpp

@@ -837,11 +837,13 @@ TEST(List_NestedCollection_Links)
     auto origin = tr->add_table("origin");
     auto list_col = origin->add_column_list(type_Mixed, "any_list");
     auto any_col = origin->add_column(type_Mixed, "any");
+    auto any1_col = origin->add_column(type_Mixed, "any1");
     auto embedded_col = origin->add_column(*embedded, "sub");
 
     Obj target_obj1 = target->create_object();
     Obj target_obj2 = target->create_object();
     Obj target_obj3 = target->create_object();
+    Obj target_obj4 = target->create_object();
     Obj parent = origin->create_object();
     parent.create_and_set_linked_object(embedded_col);
     auto child_obj = parent.get_linked_object(embedded_col);
@@ -877,6 +879,8 @@ TEST(List_NestedCollection_Links)
         dict_any = o.get_dictionary(any_col);
         dict_any.insert("Godbye", target_obj1.get_link());
         CHECK_THROW_ANY(dict_any.insert("Wrong", child_obj.get_link()));
+        o.set_collection(any1_col, CollectionType::List);
+        o.get_list<Mixed>(any1_col).add(target_obj4.get_link());
 
         // Create link from a list nested in a collection nested in a Mixed property
         dict_any.insert_collection("List", CollectionType::List);
@@ -887,6 +891,7 @@ TEST(List_NestedCollection_Links)
         CHECK_EQUAL(target_obj1.get_backlink_count(), 2);
         CHECK_EQUAL(target_obj2.get_backlink_count(), 1);
         CHECK_EQUAL(target_obj3.get_backlink_count(), 1);
+        CHECK_EQUAL(target_obj4.get_backlink_count(), 1);
     };
 
     create_links();
@@ -917,15 +922,28 @@ TEST(List_NestedCollection_Links)
     CHECK_EQUAL(target_obj2.get_backlink_count(), 1);
     o.remove();
     CHECK_EQUAL(target_obj2.get_backlink_count(), 0);
+    CHECK_EQUAL(target_obj4.get_backlink_count(), 0);
     tr->commit_and_continue_as_read();
 
     create_links();
     // Clearing dictionary should remove links
     tr->promote_to_write();
     dict_any.clear();
-    tr->commit_and_continue_as_read();
     CHECK_EQUAL(target_obj1.get_backlink_count(), 1);
     CHECK_EQUAL(target_obj3.get_backlink_count(), 0);
+    o.remove();
+    tr->commit_and_continue_as_read();
+
+    create_links();
+    tr->promote_to_write();
+    // Removing the top object should remove all backlinks.
+    // This includes the links contained in the collections
+    // held by the any (dictionary) and any1 (list) properties.
+    o.remove();
+    CHECK_EQUAL(target_obj1.get_backlink_count(), 0);
+    CHECK_EQUAL(target_obj2.get_backlink_count(), 0);
+    CHECK_EQUAL(target_obj3.get_backlink_count(), 0);
+    CHECK_EQUAL(target_obj4.get_backlink_count(), 0);
 }
 
 TEST(List_NestedCollection_Unresolved)