From 676403ecdacc37f1bf2434a2ab471f570e093a2c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=B8rgen=20Edelbo?= <jorgen.edelbo@mongodb.com>
Date: Fri, 9 Apr 2021 09:25:16 +0200
Subject: [PATCH] Update after review

---
 src/realm/query.cpp        |  6 ++++--
 src/realm/query_engine.cpp | 13 +++----------
 test/test_query2.cpp       | 13 +++++++++++++
 3 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/src/realm/query.cpp b/src/realm/query.cpp
index 33acb9f6d8c..d2436ae4ba1 100644
--- a/src/realm/query.cpp
+++ b/src/realm/query.cpp
@@ -416,9 +416,11 @@ std::unique_ptr<ParentNode> make_condition_node(const Table& table, ColKey colum
                 else if (value.is_type(type_TypedLink)) {
                     ObjLink link = value.get_link();
                     auto target_table = table.get_link_target(column_key);
-                    if (target_table->get_key() == link.get_table_key()) {
-                        key = link.get_obj_key();
+                    if (target_table->get_key() != link.get_table_key()) {
+                        // This will never match
+                        return std::unique_ptr<ParentNode>{new ExpressionNode(std::make_unique<FalseExpression>())};
                     }
+                    key = link.get_obj_key();
                 }
                 return std::unique_ptr<ParentNode>{new LinksToNode<Cond>(column_key, key)};
             }
diff --git a/src/realm/query_engine.cpp b/src/realm/query_engine.cpp
index ddabde7459b..864d2e27d24 100644
--- a/src/realm/query_engine.cpp
+++ b/src/realm/query_engine.cpp
@@ -711,12 +711,9 @@ size_t LinksToNode<Equal>::find_first_local(size_t start, size_t end)
     }
     else if (m_column_type == col_type_Link) {
         for (auto& key : m_target_keys) {
-            if (key) {
-                // LinkColumn stores link to row N as the integer N + 1
-                auto pos = static_cast<const ArrayKey*>(m_leaf_ptr)->find_first(key, start, end);
-                if (pos != realm::npos) {
-                    return pos;
-                }
+            auto pos = static_cast<const ArrayKey*>(m_leaf_ptr)->find_first(key, start, end);
+            if (pos != realm::npos) {
+                return pos;
             }
         }
     }
@@ -732,10 +729,6 @@ size_t LinksToNode<NotEqual>::find_first_local(size_t start, size_t end)
     ObjKey key = m_target_keys[0];
 
     if (m_column_type == col_type_LinkList || m_condition_column_key.is_set()) {
-        if (!key) {
-            // Null key is never found in link lists
-            return start;
-        }
         BPlusTree<ObjKey> links(m_table.unchecked_ptr()->get_alloc());
         for (size_t i = start; i < end; i++) {
             if (ref_type ref = static_cast<const ArrayList*>(m_leaf_ptr)->get(i)) {
diff --git a/test/test_query2.cpp b/test/test_query2.cpp
index a413aa66461..ed3aa7270b9 100644
--- a/test/test_query2.cpp
+++ b/test/test_query2.cpp
@@ -5216,10 +5216,16 @@ TEST(Query_LinksTo)
     q = source->column<Link>(col_link).is_null();
     tv = q.find_all();
     CHECK_EQUAL(tv.size(), 6);
+    q = source->where().equal(col_link, Mixed()); // Null
+    tv = q.find_all();
+    CHECK_EQUAL(tv.size(), 6);
 
     q = source->column<Link>(col_link) != null();
     found_key = q.find();
     CHECK_EQUAL(found_key, source_keys[2]);
+    q = source->where().not_equal(col_link, Mixed()); // Null
+    tv = q.find_all();
+    CHECK_EQUAL(tv.size(), 4);
 
     auto linklist = source->get_object(source_keys[1]).get_linklist_ptr(col_linklist);
     linklist->add(target_keys[6]);
@@ -5246,6 +5252,13 @@ TEST(Query_LinksTo)
     q = source->where().not_equal(col_linklist, Mixed(target_keys[6]));
     tv = q.find_all();
     CHECK_EQUAL(tv.size(), 2);
+
+    q = source->where().equal(col_linklist, Mixed());
+    tv = q.find_all();
+    CHECK_EQUAL(tv.size(), 0); // LinkList never matches null
+    q = source->where().not_equal(col_linklist, Mixed());
+    tv = q.find_all();
+    CHECK_EQUAL(tv.size(), 3);
 }
 
 TEST(Query_Group_bug)