SERVER-58437 Implement pushdown logic for $lookup

2 files changed, 10 insertions, 1 deletions

diff --git a/src/mongo/db/query/get_executor.cpp b/src/mongo/db/query/get_executor.cpp
index cd61dfefe7c..a08402df756 100644
--- a/src/mongo/db/query/get_executor.cpp
+++ b/src/mongo/db/query/get_executor.cpp
@@ -962,7 +962,7 @@ public:
 
     std::pair<std::unique_ptr<sbe::PlanStage>, stage_builder::PlanStageData> buildExecutableTree(
         const QuerySolution& solution) const final {
-        // TODO SERVER-58437 We don't pass '_collections' to the function below because at the
+        // TODO SERVER-62677 We don't pass '_collections' to the function below because at the
         // moment, no pushdown is actually happening. This should be changed once the logic for
         // pushdown is implemented.
         return stage_builder::buildSlotBasedExecutableTree(
diff --git a/src/mongo/db/query/multi_collection.h b/src/mongo/db/query/multi_collection.h
index 77368d13682..9b3230a2cc6 100644
--- a/src/mongo/db/query/multi_collection.h
+++ b/src/mongo/db/query/multi_collection.h
@@ -80,6 +80,15 @@ public:
         return _secondaryColls;
     }
 
+    const CollectionPtr& lookupCollection(const NamespaceString& nss) const {
+        if (_mainCollName && nss == *_mainCollName) {
+            return *_mainColl;
+        } else if (auto itr = _secondaryColls.find(nss); itr != _secondaryColls.end()) {
+            return itr->second;
+        }
+        return CollectionPtr::null;
+    }
+
     void clear() {
         _mainColl = &CollectionPtr::null;
         _secondaryColls.clear();