1 files changed, 76 insertions, 0 deletions
diff --git a/jstests/core/existsb.js b/jstests/core/existsb.js
new file mode 100644
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+++ b/jstests/core/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.ensureIndex({ a : 1 });
+checkExistsNull();
+
+// try with a sparse index
+t.dropIndexes();
+t.ensureIndex({ a : 1 }, { sparse:true });
+checkExistsNull();
+
+// try with a compound index
+t.dropIndexes();
+t.ensureIndex({ a : 1, b : 1 });
+checkExistsNull();
+
+// try with sparse compound index
+t.dropIndexes();
+t.ensureIndex({ a : 1, b : 1 }, { sparse:true });
+checkExistsNull();