Can pick index with more key specificity than required by sort / find spec

4 files changed, 30 insertions, 9 deletions

diff --git a/db/jsobj.cpp b/db/jsobj.cpp
index 16bbbdd4b1f..e7c8862119c 100644
--- a/db/jsobj.cpp
+++ b/db/jsobj.cpp
@@ -739,6 +739,13 @@ namespace mongo {
         }
         return b.done();
     }
+
+    /**
+     sets element field names to empty string
+     If a field in pattern is missing, it is omitted from the returned
+     object.  Unlike extractFieldsDotted, it does not return an empty
+     object on missing pattern field.
+     */
     BSONObj BSONObj::extractFieldsUnDotted(BSONObj pattern) const {
         BSONObjBuilder b;
         BSONObjIterator i(pattern);
@@ -747,9 +754,8 @@ namespace mongo {
             if ( e.eoo() )
                 break;
             BSONElement x = getField(e.fieldName());
-            if ( x.eoo() )
-                return BSONObj();
-            b.appendAs(x, "");
+            if ( !x.eoo() )
+                b.appendAs(x, "");
         }
         return b.obj();
     }
diff --git a/db/jsobj.h b/db/jsobj.h
index 55bf59314a8..26b0a40dd0a 100644
--- a/db/jsobj.h
+++ b/db/jsobj.h
@@ -566,6 +566,9 @@ namespace mongo {
         
         /**
            sets element field names to empty string
+           If a field in pattern is missing, it is omitted from the returned
+           object.  Unlike extractFieldsDotted, it does not return an empty
+           object on missing pattern field.
         */
         BSONObj extractFieldsUnDotted(BSONObj pattern) const;
         
diff --git a/db/query.cpp b/db/query.cpp
index 33def1372ec..5195dea984a 100644
--- a/db/query.cpp
+++ b/db/query.cpp
@@ -58,11 +58,11 @@ namespace mongo {
         while ( 1 ) {
             BSONElement ie = i.next();
             BSONElement se = s.next();
-            if ( ie.eoo() ) {
-                if ( !se.eoo() )
-                    return 0;
+            if ( ie.eoo() && !se.eoo() )
+                return 0;
+            if ( ie.eoo() || se.eoo() )
                 return direction;
-            }
+
             if ( strcmp( ie.fieldName(), se.fieldName() ) != 0 )
                 return 0;
 
@@ -146,6 +146,11 @@ namespace mongo {
 
         set<string> queryFields;
         query.getFieldNames(queryFields);
+        if ( queryFields.size() == 0 ) {
+            DEV out() << "getIndexCursor fail " << ns << '\n';
+            return auto_ptr<Cursor>();            
+        }
+        
         // regular query without order by
         for (int i = 0; i < d->nIndexes; i++ ) {
             BSONObj idxInfo = d->indexes[i].info.obj(); // { name:, ns:, key: }
@@ -153,7 +158,12 @@ namespace mongo {
             set<string> keyFields;
             idxKey.getFieldNames(keyFields);
 
-            if ( keyFields == queryFields ) {
+            bool subset = true;
+            for( set<string>::iterator j = queryFields.begin(); subset && j != queryFields.end(); ++j )
+                if ( keyFields.count( *j ) == 0 )
+                    subset = false;
+            
+            if ( subset ) {
                 BSONObj q = query.extractFieldsUnDotted(idxKey);
                 assert(q.objsize() != 0); // guard against a seg fault if details is 0
                                                                                                                
diff --git a/jstests/index7.js b/jstests/index7.js
index 7bd46a82568..bfbe9c8e07f 100644
--- a/jstests/index7.js
+++ b/jstests/index7.js
@@ -42,12 +42,14 @@ f.drop();
 f.ensureIndex( { a: 1, b: 1 } );
 index( f.find().sort( { a: 1, b: 1 } ) );
 index( f.find().sort( { a: -1, b: -1 } ) );
+index( f.find().sort( { a: 1 } ) );
+index( f.find().sort( { a: 1 } ).hint( { a: 1, b: 1 } ) );
 noIndex( f.find().sort( { a: 1, b: -1 } ) );
 noIndex( f.find().sort( { b: 1, a: 1 } ) );
 
 noIndex( f.find() );
 noIndex( f.find( { c: 1 } ) );
-noIndex( f.find( { a: 1 } ) ); // Once we enhance the query optimizer, this should get an index.
+index( f.find( { a: 1 } ) );
 index( f.find( { a: 1, b: 1 } ) );
 index( f.find( { b: 1, a: 1 } ) );