From 273dda0b61a10084798dc59d455ea735d19074bc Mon Sep 17 00:00:00 2001
From: Aaron <aaron@10gen.com>
Date: Fri, 25 Mar 2011 11:04:49 -0700
Subject: [PATCH] SERVER-2829 doc

---
 db/matcher.cpp | 4 +++-
 db/matcher.h   | 7 ++++++-
 jstests/in8.js | 2 ++
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/db/matcher.cpp b/db/matcher.cpp
index aa61705a5a91a..5674f29a64f60 100644
--- a/db/matcher.cpp
+++ b/db/matcher.cpp
@@ -419,7 +419,7 @@ namespace mongo {
 
     Matcher::Matcher( const Matcher &other, const BSONObj &key ) :
         where(0), constrainIndexKey_( key ), haveSize(), all(), hasArray(0), haveNeg(), _atomic(false), nRegex(0) {
-        // do not include fields which would make keyMatch() false
+        // do not include field matches which would make keyMatch() false
         for( vector< ElementMatcher >::const_iterator i = other.basics.begin(); i != other.basics.end(); ++i ) {
             if ( key.hasField( i->toMatch.fieldName() ) ) {
                 switch( i->compareOp ) {
@@ -436,12 +436,14 @@ namespace mongo {
                             break;
                         }
                     }
+                    // Can't match an array to its first indexed element.
                     if ( !i->isNot && !inContainsArray ) {
                         basics.push_back( *i );
                     }
                     break;
                 }
                 default: {
+                    // Can't match an array to its first indexed element.
                     if ( !i->isNot && i->toMatch.type() != Array ) {
                         basics.push_back( *i );
                     }
diff --git a/db/matcher.h b/db/matcher.h
index d242df64452dc..36591656ffefe 100644
--- a/db/matcher.h
+++ b/db/matcher.h
@@ -143,7 +143,12 @@ namespace mongo {
         // fast rough check to see if we must load the real doc - we also
         // compare field counts against covereed index matcher; for $or clauses
         // we just compare field counts
-        bool keyMatch() const { return !all && !haveSize && !hasArray && !haveNeg; }
+        bool keyMatch() const { return
+            !all
+            && !haveSize
+            && !hasArray // We can't match an array to its first indexed element using keymatch
+            && !haveNeg;
+        }
 
         bool atomic() const { return _atomic; }
 
diff --git a/jstests/in8.js b/jstests/in8.js
index dd56e0e5efb99..0620c0917ef82 100644
--- a/jstests/in8.js
+++ b/jstests/in8.js
@@ -10,6 +10,8 @@ t.save( {key: [[2]]} );
 function doTest() { 
     assert.eq( 1, t.count( {key:[1]} ) );
     assert.eq( 1, t.count( {key:{$in:[[1]]}} ) );
+    assert.eq( 1, t.count( {key:{$in:[[1]],$ne:[2]}} ) );
+    assert.eq( 1, t.count( {key:{$in:[[1]],$type:1}} ) );
     assert.eq( 1, t.count( {key:['1']} ) );
     assert.eq( 1, t.count( {key:{$in:[['1']]}} ) );
     assert.eq( 1, t.count( {key:[2]} ) );