1 files changed, 76 insertions, 0 deletions
diff --git a/jstests/core/query/exists/existsb.js b/jstests/core/query/exists/existsb.js
new file mode 100644
index 00000000000..64ee3cf9a88
--- /dev/null
+++ b/jstests/core/query/exists/existsb.js
@@ -0,0 +1,76 @@
+// Tests for $exists against documents that store a null value
+//
+// A document with a missing value for an indexed field
+// is indexed *as if* it had the value 'null' explicitly.
+// Therefore:
+//     { b : 1 }
+//     { a : null, b : 1 }
+// look identical based on a standard index on { a : 1 }.
+//
+// -- HOWEVER!! --
+// A sparse index on { a : 1 } would include { a : null, b : 1 },
+// but would not include { b : 1 }.  In this case, the two documents
+// are treated equally.
+//
+// Also, super special edge case around sparse, compound indexes
+// from Mathias:
+//   If we have a sparse index on { a : 1, b : 1 }
+//   And we insert docs {}, { a : 1 },
+//                      { b : 1 }, and { a : 1, b : 1 }
+//   everything but {} will have an index entry.
+// Let's make sure we handle this properly!
+
+t = db.jstests_existsb;
+t.drop();
+
+t.save({});
+t.save({a: 1});
+t.save({b: 1});
+t.save({a: 1, b: null});
+t.save({a: 1, b: 1});
+
+/** run a series of checks, just on the number of docs found */
+function checkExistsNull() {
+    // Basic cases
+    assert.eq(3, t.count({a: {$exists: true}}));
+    assert.eq(2, t.count({a: {$exists: false}}));
+    assert.eq(3, t.count({b: {$exists: true}}));
+    assert.eq(2, t.count({b: {$exists: false}}));
+    // With negations
+    assert.eq(3, t.count({a: {$not: {$exists: false}}}));
+    assert.eq(2, t.count({a: {$not: {$exists: true}}}));
+    assert.eq(3, t.count({b: {$not: {$exists: false}}}));
+    assert.eq(2, t.count({b: {$not: {$exists: true}}}));
+    // Both fields
+    assert.eq(2, t.count({a: 1, b: {$exists: true}}));
+    assert.eq(1, t.count({a: 1, b: {$exists: false}}));
+    assert.eq(1, t.count({a: {$exists: true}, b: 1}));
+    assert.eq(1, t.count({a: {$exists: false}, b: 1}));
+    // Both fields, both $exists
+    assert.eq(2, t.count({a: {$exists: true}, b: {$exists: true}}));
+    assert.eq(1, t.count({a: {$exists: true}, b: {$exists: false}}));
+    assert.eq(1, t.count({a: {$exists: false}, b: {$exists: true}}));
+    assert.eq(1, t.count({a: {$exists: false}, b: {$exists: false}}));
+}
+
+// with no index, make sure we get correct results
+checkExistsNull();
+
+// try with a standard index
+t.createIndex({a: 1});
+checkExistsNull();
+
+// try with a sparse index
+t.dropIndexes();
+t.createIndex({a: 1}, {sparse: true});
+checkExistsNull();
+
+// try with a compound index
+t.dropIndexes();
+t.createIndex({a: 1, b: 1});
+checkExistsNull();
+
+// try with sparse compound index
+t.dropIndexes();
+t.createIndex({a: 1, b: 1}, {sparse: true});
+checkExistsNull();