1 files changed, 28 insertions, 22 deletions
diff --git a/src/mongo/db/pipeline/dependencies.cpp b/src/mongo/db/pipeline/dependencies.cpp
index bb6b7175ae5..a1fc3b88a19 100644
--- a/src/mongo/db/pipeline/dependencies.cpp
+++ b/src/mongo/db/pipeline/dependencies.cpp
@@ -41,34 +41,40 @@ using std::vector;
 
 namespace str = mongoutils::str;
 
-BSONObj DepsTracker::toProjection() const {
-    if (fields.empty() && !needWholeDocument) {
-        if (_needTextScore) {
-            // We only need the text score, but there is no easy way to express this in the query
-            // projection language. We use $noFieldsNeeded with a textScore meta-projection since
-            // this is an inclusion projection which will exclude all existing fields but add the
-            // textScore metadata.
-            return BSON("_id" << 0 << "$noFieldsNeeded" << 1 << Document::metaFieldTextScore
-                              << BSON("$meta"
-                                      << "textScore"));
-        } else {
-            // We truly need no information (we are doing a count or something similar). In this
-            // case, the DocumentSourceCursor will know there aren't any dependencies, and we can
-            // ignore the documents returned from the query system. We pass an empty object as the
-            // projection so that we have a chance of using the COUNT_SCAN optimization.
-            return BSONObj();
-        }
+bool DepsTracker::_appendMetaProjections(BSONObjBuilder* projectionBuilder) const {
+    if (_needTextScore) {
+        projectionBuilder->append(Document::metaFieldTextScore,
+                                  BSON("$meta"
+                                       << "textScore"));
     }
+    if (_needSortKey) {
+        projectionBuilder->append(Document::metaFieldSortKey,
+                                  BSON("$meta"
+                                       << "sortKey"));
+    }
+    return (_needTextScore || _needSortKey);
+}
 
+BSONObj DepsTracker::toProjection() const {
     BSONObjBuilder bb;
 
-    if (_needTextScore)
-        bb.append(Document::metaFieldTextScore,
-                  BSON("$meta"
-                       << "textScore"));
+    const bool needsMetadata = _appendMetaProjections(&bb);
 
-    if (needWholeDocument)
+    if (needWholeDocument) {
         return bb.obj();
+    }
+
+    if (fields.empty()) {
+        if (needsMetadata) {
+            // We only need metadata, but there is no easy way to express this in the query
+            // projection language. We use $noFieldsNeeded with a meta-projection since this is an
+            // inclusion projection which will exclude all existing fields but add the metadata.
+            bb.append("_id", 0);
+            bb.append("$noFieldsNeeded", 1);
+        }
+        // We either need nothing (as we would if this was logically a count), or only the metadata.
+        return bb.obj();
+    }
 
     bool needId = false;
     string last;