SERVER-1752 SERVER-4529 Do not incorrectly use fast count mode when matching against a null value.

1 files changed, 28 insertions, 9 deletions

diff --git a/jstests/indexy.js b/jstests/indexy.js
index 3f52f16590d..def63743785 100644
--- a/jstests/indexy.js
+++ b/jstests/indexy.js
@@ -1,16 +1,35 @@
-// Test count matching when null key is generated even though it should not be matched in a standard query. SERVER-4529
+// Null index keys may be generated for documents that do not match null.  In particular, for index
+// { 'a.c':1 } the document { a:[ {}, { c:10 } ] } generates index keys { '':null } and { '':10 }.
+// While the query { a:{ $elemMatch:{ c:null } } } has been designated to match this document, the
+// query { 'a.c':null } has been designated to not match this document.
+//
+// Because the above and similar queries do not match the document but do match documents lacking
+// any 'a.c' field (which also generate a { '':null } key), a Matcher is required when it is
+// necessary to select matching documents for these queries.  As a result, the fast count in which
+// the matcher is bypassed (SERVER-1752) cannot be used for such queries.  The following tests check
+// that the count is calculated correctly in cases where fast count mode should not be applied.
+//
+// SERVER-4529
 
 t = db.jstests_indexy;
 t.drop();
 
-t.save({a:[{},{c:10}]});
+function assertNoMatch( query ) {
+    // Check that no results are returned by a find.
+    assert.eq( 0, t.find( query ).itcount() );
+    // Check that no results are counted by a count.
+    assert.eq( 0, t.find( query ).count() );
+}
 
-assert.eq( 0, t.find({'a.c':null}).itcount() );
-assert.eq( 0, t.find({'a.c':null}).count() );
+t.save({a:[{},{c:10}]});
+assertNoMatch( { 'a.c':null } );
 
 t.ensureIndex({'a.c':1});
-
-assert.eq( 0, t.find({'a.c':null}).itcount() );
-if( 0 ) { // SERVER-4529
-assert.eq( 0, t.find({'a.c':null}).count() );
-}
+// No equality match against null.
+assertNoMatch( { 'a.c':null } );
+// No $in match against null.
+assertNoMatch( { 'a.c':{ $in:[ null ] } } );
+assertNoMatch( { 'a.c':{ $in:[ null, 1 ] } } );
+// No match for a query generating the field range [[ minkey, {} ]], which includes the value null,
+// on the field 'a.c'.
+assertNoMatch( { 'a.c':{ $lt:{} } } );