SERVER-12129 meta projection operator should overwrite fields

3 files changed, 40 insertions, 2 deletions

diff --git a/src/mongo/db/exec/projection_exec.cpp b/src/mongo/db/exec/projection_exec.cpp
index 05a33a24002..15a224cbe72 100644
--- a/src/mongo/db/exec/projection_exec.cpp
+++ b/src/mongo/db/exec/projection_exec.cpp
@@ -479,6 +479,14 @@ namespace mongo {
                                   const MatchDetails* details,
                                   const ArrayOpType arrayOpType) const {
 
+
+        // Skip if the field name matches a computed $meta field.
+        // $meta projection fields can exist at the top level of
+        // the result document and the field names cannot be dotted.
+        if (_meta.find(elt.fieldName()) != _meta.end()) {
+            return Status::OK();
+        }
+
         FieldMap::const_iterator field = _fields.find(elt.fieldName());
         if (field == _fields.end()) {
             if (_include) {
diff --git a/src/mongo/db/exec/projection_exec.h b/src/mongo/db/exec/projection_exec.h
index eefeb5e8c9a..796e8c62283 100644
--- a/src/mongo/db/exec/projection_exec.h
+++ b/src/mongo/db/exec/projection_exec.h
@@ -178,10 +178,10 @@ namespace mongo {
 
         ArrayOpType _arrayOpType;
 
-        // Is there an elemMatch or positional operator?
+        // Is there an slice, elemMatch or meta operator?
         bool _hasNonSimple;
 
-        // Is there a projection over a dotted field?
+        // Is there a projection over a dotted field or a $ positional operator?
         bool _hasDottedField;
 
         // The full query expression.  Used when we need MatchDetails.
diff --git a/src/mongo/db/exec/projection_exec_test.cpp b/src/mongo/db/exec/projection_exec_test.cpp
index 6267f32fabe..59af37dd6d4 100644
--- a/src/mongo/db/exec/projection_exec_test.cpp
+++ b/src/mongo/db/exec/projection_exec_test.cpp
@@ -34,6 +34,7 @@
 
 #include <memory>
 #include "mongo/db/json.h"
+#include "mongo/db/exec/working_set_computed_data.h"
 #include "mongo/db/matcher/expression_parser.h"
 #include "mongo/unittest/unittest.h"
 
@@ -64,12 +65,14 @@ namespace {
      * specStr - projection specification
      * queryStr - query
      * objStr - object to run projection on
+     * data - computed data. Owned by working set member created in this function if not null.
      * expectedStatusOK - expected status of transformation
      * expectedObjStr - expected object after successful projection.
      *                  Ignored if expectedStatusOK is false.
      */
 
     void testTransform(const char* specStr, const char* queryStr, const char* objStr,
+                       WorkingSetComputedData* data,
                        bool expectedStatusOK, const char* expectedObjStr) {
         // Create projection exec object.
         BSONObj spec = fromjson(specStr);
@@ -81,6 +84,9 @@ namespace {
         WorkingSetMember wsm;
         wsm.state = WorkingSetMember::OWNED_OBJ;
         wsm.obj = fromjson(objStr);
+        if (data) {
+            wsm.addComputed(data);
+        }
 
         // Transform object
         Status status = exec.transform(&wsm);
@@ -125,6 +131,14 @@ namespace {
         }
     }
 
+    /**
+     * testTransform without computed data argument.
+     */
+    void testTransform(const char* specStr, const char* queryStr, const char* objStr,
+                       bool expectedStatusOK, const char* expectedObjStr) {
+        testTransform(specStr, queryStr, objStr, NULL, expectedStatusOK, expectedObjStr);
+    }
+
     //
     // position $
     //
@@ -186,4 +200,20 @@ namespace {
         testTransform("{a: {$slice: [10, 10]}}", "{}", "{a: [4, 6, 8]}", true, "{a: []}");
     }
 
+    //
+    // $meta
+    // $meta projections add computed values to the projected object.
+    //
+
+    TEST(ProjectionExecTest, TransformMetaTextScore) {
+        // Query {} is ignored.
+        testTransform("{b: {$meta: 'textScore'}}", "{}", "{a: 'hello'}",
+                      new mongo::TextScoreComputedData(100),
+                      true, "{a: 'hello', b: 100}");
+        // Projected meta field should overwrite existing field.
+        testTransform("{b: {$meta: 'textScore'}}", "{}", "{a: 'hello', b: -1}",
+                      new mongo::TextScoreComputedData(100),
+                      true, "{a: 'hello', b: 100}");
+    }
+
 }  // namespace