From 2f2b9ab58fbc54249187c3280271ff49c5bbbd71 Mon Sep 17 00:00:00 2001
From: Louis Chatriot <louis.chatriot@gmail.com>
Date: Sat, 22 Jun 2013 18:11:07 +0200
Subject: [PATCH] Implemented  comparator

---
 lib/model.js       | 14 ++++++++++++++
 test/model.test.js | 20 +++++++++++++++++++-
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/lib/model.js b/lib/model.js
index 16e1016..ba70bf2 100644
--- a/lib/model.js
+++ b/lib/model.js
@@ -503,6 +503,20 @@ comparisonFunctions.$nin = function (a, b) {
   return !comparisonFunctions.$in(a, b);
 };
 
+comparisonFunctions.$exists = function (value, exists) {
+  if (exists || exists === '') {   // This will be true for all values of exists except false, null, undefined and 0
+    exists = true;                 // That's strange behaviour (we should only use true/false) but that's the way Mongo does it...
+  } else {
+    exists = false;
+  }
+
+  if (value === undefined) {
+    return !exists
+  } else {
+    return exists;
+  }
+};
+
 
 /**
  * Match any of the subqueries
diff --git a/test/model.test.js b/test/model.test.js
index 44ed540..ad02e57 100644
--- a/test/model.test.js
+++ b/test/model.test.js
@@ -770,7 +770,7 @@ describe('Model', function () {
 
 
     // General behaviour is tested in the block about $lt. Here we just test operators work
-    describe('Other comparison operators: $lte, $gt, $gte, $ne, $in', function () {
+    describe('Other comparison operators: $lte, $gt, $gte, $ne, $in, $exists', function () {
 
       it('$lte', function () {
         model.match({ a: 5 }, { a: { $lte: 6 } }).should.equal(true);
@@ -819,6 +819,24 @@ describe('Model', function () {
         (function () { model.match({ a: 5 }, { a: { $in: 5 } }); }).should.throw();
       });
 
+      it('$exists', function () {
+        model.match({ a: 5 }, { a: { $exists: 1 } }).should.equal(true);
+        model.match({ a: 5 }, { a: { $exists: true } }).should.equal(true);
+        model.match({ a: 5 }, { a: { $exists: new Date() } }).should.equal(true);
+        model.match({ a: 5 }, { a: { $exists: '' } }).should.equal(true);
+        model.match({ a: 5 }, { a: { $exists: [] } }).should.equal(true);
+        model.match({ a: 5 }, { a: { $exists: {} } }).should.equal(true);
+
+        model.match({ a: 5 }, { a: { $exists: 0 } }).should.equal(false);
+        model.match({ a: 5 }, { a: { $exists: false } }).should.equal(false);
+        model.match({ a: 5 }, { a: { $exists: null } }).should.equal(false);
+        model.match({ a: 5 }, { a: { $exists: undefined } }).should.equal(false);
+
+        model.match({ a: 5 }, { b: { $exists: true } }).should.equal(false);
+
+        model.match({ a: 5 }, { b: { $exists: false } }).should.equal(true);
+      });
+
     });