Refactor link tracing code (#5796)

* refactor link tracing code

* LinkTranslator gets a separate file

* update changelog

* review feedback

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?.?.?)
+* Prevent migrations to an embedded object type when there are incoming links from Mixed/TypedLink properties until we can support them. ([#5796](https://github.com/realm/realm-core/pull/5796))
 * Fix a data race on RealmCoordinator::m_sync_session which could occur if multiple threads performed the initial open of a Realm at once. (since v11.8.0).
 * If a SyncSession outlived the parent Realm and then was adopted by a new Realm for the same file, other processes would not get notified for sync writes on that file.
 * Fix one cause of QoS inversion warnings when performing writes on the main thread on Apple platforms. Waiting for async notifications to be ready is now done in a QoS-aware ways.

Package.swift

@@ -75,6 +75,7 @@ let notSyncServerSources: [String] = [
  "realm/history.cpp",
  "realm/impl",
  "realm/index_string.cpp",
+ "realm/link_translator.cpp",
  "realm/list.cpp",
  "realm/mixed.cpp",
  "realm/node.cpp",

src/realm/CMakeLists.txt

@@ -41,6 +41,7 @@ set(REALM_SOURCES
  impl/simulated_failure.cpp
  impl/transact_log.cpp
  index_string.cpp
+ link_translator.cpp
  list.cpp
  node.cpp
  mixed.cpp

src/realm/link_translator.cpp

@@ -0,0 +1,94 @@
+/*************************************************************************
+ *
+ * Copyright 2022 Realm Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ **************************************************************************/
+
+#include "realm/link_translator.hpp"
+
+#include <realm/dictionary.hpp>
+#include <realm/list.hpp>
+#include <realm/set.hpp>
+
+namespace realm {
+
+LinkTranslator::LinkTranslator(Obj origin, ColKey origin_col_key)
+ : m_origin_obj(origin)
+ , m_origin_col_key(origin_col_key)
+{
+}
+
+void LinkTranslator::run()
+{
+ ColumnAttrMask attr = m_origin_col_key.get_attrs();
+ if (attr.test(col_attr_List)) {
+ if (m_origin_col_key.get_type() == col_type_LinkList) {
+ LnkLst link_list = m_origin_obj.get_linklist(m_origin_col_key);
+ on_list_of_links(link_list);
+ }
+ else if (m_origin_col_key.get_type() == col_type_Mixed) {
+ Lst<Mixed> list = m_origin_obj.get_list<Mixed>(m_origin_col_key);
+ on_list_of_mixed(list);
+ }
+ else if (m_origin_col_key.get_type() == col_type_TypedLink) {
+ Lst<ObjLink> list = m_origin_obj.get_list<ObjLink>(m_origin_col_key);
+ on_list_of_typedlink(list);
+ }
+ else {
+ throw std::runtime_error(
+ util::format("LinkTranslator unhandled list type: %1", m_origin_col_key.get_type()));
+ }
+ }
+ else if (attr.test(col_attr_Set)) {
+ if (m_origin_col_key.get_type() == col_type_Link) {
+ LnkSet set = m_origin_obj.get_linkset(m_origin_col_key);
+ on_set_of_links(set);
+ }
+ else if (m_origin_col_key.get_type() == col_type_Mixed) {
+ Set<Mixed> set = m_origin_obj.get_set<Mixed>(m_origin_col_key);
+ on_set_of_mixed(set);
+ }
+ else if (m_origin_col_key.get_type() == col_type_TypedLink) {
+ Set<ObjLink> set = m_origin_obj.get_set<ObjLink>(m_origin_col_key);
+ on_set_of_typedlink(set);
+ }
+ else {
+ throw std::runtime_error(
+ util::format("LinkTranslator unhandled set type: %1", m_origin_col_key.get_type()));
+ }
+ }
+ else if (attr.test(col_attr_Dictionary)) {
+ auto dict = m_origin_obj.get_dictionary(m_origin_col_key);
+ on_dictionary(dict);
+ }
+ else {
+ REALM_ASSERT_EX(!m_origin_col_key.is_collection(), m_origin_col_key);
+ if (m_origin_col_key.get_type() == col_type_Link) {
+ on_link_property(m_origin_col_key);
+ }
+ else if (m_origin_col_key.get_type() == col_type_Mixed) {
+ on_mixed_property(m_origin_col_key);
+ }
+ else if (m_origin_col_key.get_type() == col_type_TypedLink) {
+ on_typedlink_property(m_origin_col_key);
+ }
+ else {
+ throw std::runtime_error(
+ util::format("LinkTranslator unhandled property type: %1", m_origin_col_key.get_type()));
+ }
+ }
+}
+
+} // namespace realm

src/realm/link_translator.hpp

@@ -0,0 +1,54 @@
+/*************************************************************************
+ *
+ * Copyright 2022 Realm Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ **************************************************************************/
+
+#ifndef REALM_LINK_TRANSLATOR_HPP
+#define REALM_LINK_TRANSLATOR_HPP
+
+#include <realm/obj.hpp>
+
+namespace realm {
+
+// This construct is used when code needs to handle all
+// possible link column types. Subclass and override all
+// methods to handle each type. A good example of where
+// this is useful is when following a backlink to its
+// origin column and modifying the outgoing link from
+// whatever container it came from.
+class LinkTranslator {
+public:
+ LinkTranslator(Obj origin, ColKey origin_col_key);
+ void run();
+ virtual void on_list_of_links(LnkLst& list) = 0;
+ virtual void on_list_of_mixed(Lst<Mixed>& list) = 0;
+ virtual void on_list_of_typedlink(Lst<ObjLink>& list) = 0;
+ virtual void on_set_of_links(LnkSet& set) = 0;
+ virtual void on_set_of_mixed(Set<Mixed>& set) = 0;
+ virtual void on_set_of_typedlink(Set<ObjLink>& set) = 0;
+ virtual void on_dictionary(Dictionary& dict) = 0;
+ virtual void on_link_property(ColKey col) = 0;
+ virtual void on_mixed_property(ColKey col) = 0;
+ virtual void on_typedlink_property(ColKey col) = 0;
+
+protected:
+ Obj m_origin_obj;
+ ColKey m_origin_col_key;
+};
+
+} // namespace realm
+
+#endif // REALM_LINK_TRANSLATOR_HPP

src/realm/list.cpp

@@ -278,10 +278,9 @@ void Lst<ObjKey>::do_clear()
  ObjKey target_key = m_tree->get(ndx);
  Obj target_obj = target_table->get_object(target_key);
  target_obj.remove_one_backlink(backlink_col, m_obj.get_key()); // Throws
- size_t num_remaining = target_obj.get_backlink_count(*origin_table, m_col_key);
- if (num_remaining == 0) {
- state.m_to_be_deleted.emplace_back(target_table_key, target_key);
- }
+ // embedded objects should only have one incoming link
+ REALM_ASSERT_EX(target_obj.get_backlink_count() == 0, target_obj.get_backlink_count());
+ state.m_to_be_deleted.emplace_back(target_table_key, target_key);
  }
 
  m_tree->clear();