Add $size query option

db/jsobj.cpp

@@ -407,6 +407,8 @@ namespace mongo {
             }
             else if ( fn[1] == 'i' && fn[2] == 'n' && fn[3] == 0 )
                 return JSMatcher::opIN;
+            else if ( fn[1] == 's' && fn[2] == 'i' && fn[3] == 'z' && fn[4] == 'e' && fn[5] == 0 )
+                return JSMatcher::opSIZE;
         }
         return JSMatcher::Equality;
     }

db/matcher.cpp

@@ -258,6 +258,14 @@ namespace mongo {
                             addBasic(e, opIN); // e not actually used at the moment for $in
                             ok = true;
                         }
+                        else if ( fn[1] == 's' && fn[2] == 'i' && fn[3] == 'z' && fn[4] == 'e' ) {
+                            uassert( "$size must be a number", fe.isNumber() );
+                            BSONObjBuilder *b = new BSONObjBuilder();
+                            builders[nBuilders++] = b;
+                            b->appendAs(fe, e.fieldName());
+                            addBasic(b->done().firstElement(), opSIZE);                            
+                            ok = true;
+                        }
                         else
                             uassert("invalid $operator", false);
                     }
@@ -289,6 +297,20 @@ namespace mongo {
             return c;
         }
 
+        if ( op == opSIZE ) {
+            if ( l.type() != Array )
+                return 0;
+            int count = 0;
+            BSONObjIterator i( l.embeddedObject() );
+            while( i.more() ) {
+                BSONElement e = i.next();
+                if ( e.eoo() )
+                    break;
+                ++count;
+            }
+            return count == r.number();
+        }
+        
         /* check LT, GTE, ... */
         if ( !( l.isNumber() && r.isNumber() ) && ( l.type() != r.type() ) )
             return false;

db/matcher.h

@@ -86,7 +86,8 @@ namespace mongo {
             GTE = 0x6,
             GT = 0x4,
             opIN = 0x8, // { x : { $in : [1,2,3] } }
-            NE = 0x9
+            NE = 0x9,
+            opSIZE = 0x10
         };
 
         static int opDirection(int op) {

dbtests/matchertests.cpp

@@ -64,6 +64,16 @@ namespace MatcherTests {
         }        
     };
 
+    class Size {
+    public:
+        void run() {
+            JSMatcher m( fromjson( "{a:{$size:4}}" ) );
+            ASSERT( m.matches( fromjson( "{a:[1,2,3,4]}" ) ) );
+            ASSERT( !m.matches( fromjson( "{a:[1,2,3]}" ) ) );
+            ASSERT( !m.matches( fromjson( "{a:[1,2,3,'a','b']}" ) ) );
+        }        
+    };
+    
     class All : public UnitTest::Suite {
     public:
         All() {
@@ -71,6 +81,7 @@ namespace MatcherTests {
             add< DoubleEqual >();
             add< MixedNumericEqual >();
             add< MixedNumericGt >();
+            add< Size >();
         }
     };
     

s/shardkey.cpp

@@ -383,6 +383,7 @@ namespace mongo {
                         break;
                     case JSMatcher::opIN:
                     case JSMatcher::NE:
+                    case JSMatcher::opSIZE:
                         massert("not implemented yet relevant()", false);
                     case JSMatcher::Equality:
                         goto normal;