Projection fully tested for cursor

lib/cursor.js

@@ -84,7 +84,11 @@ Cursor.prototype.project = function (candidates) {
   // Do the actual projection
   candidates.forEach(function (candidate) {
     var toPush = action === 1 ? _.pick(candidate, keys) : _.omit(candidate, keys);
-    if (keepId) { toPush._id = candidate._id; }
+    if (keepId) {
+      toPush._id = candidate._id;
+    } else {
+      delete toPush._id;
+    }
     res.push(toPush);
   });
 
@@ -161,7 +165,7 @@ Cursor.prototype._exec = function(callback) {
     res = this.project(res);
   } catch (e) {
     error = e;
-    res = null;
+    res = undefined;
   }
 
   if (this.execFn) {

test/cursor.test.js

@@ -719,21 +719,60 @@ describe('Cursor', function () {
         assert.deepEqual(docs[4], { age: 89, _id: doc4._id });   // No problems if one field to take doesn't exist
 
         cursor.projection({ age: 1, name: 1, _id: 0 });
+        cursor.exec(function (err, docs) {
+          assert.isNull(err);
+          docs.length.should.equal(5);
+          assert.deepEqual(docs[0], { age: 5, name: 'Jo' });
+          assert.deepEqual(docs[1], { age: 23, name: 'LM' });
+          assert.deepEqual(docs[2], { age: 52, name: 'Grafitti' });
+          assert.deepEqual(docs[3], { age: 57, name: 'Louis' });
+          assert.deepEqual(docs[4], { age: 89 });   // No problems if one field to take doesn't exist
+
+          done();
+        });
+      });
+    });
+
+    it('Can omit only the expected fields', function (done) {
+      var cursor = new Cursor(d, {});
+      cursor.sort({ age: 1 });   // For easier finding
+      cursor.projection({ age: 0, name: 0 });
       cursor.exec(function (err, docs) {
         assert.isNull(err);
         docs.length.should.equal(5);
         // Takes the _id by default
-          assert.deepEqual(docs[0], { age: 5, name: 'Jo', _id: doc0._id });
-          assert.deepEqual(docs[1], { age: 23, name: 'LM', _id: doc3._id });
-          assert.deepEqual(docs[2], { age: 52, name: 'Grafitti', _id: doc2._id });
-          assert.deepEqual(docs[3], { age: 57, name: 'Louis', _id: doc1._id });
-          assert.deepEqual(docs[4], { age: 89, _id: doc4._id });   // No problems if one field to take doesn't exist
+        assert.deepEqual(docs[0], { planet: 'B', _id: doc0._id });
+        assert.deepEqual(docs[1], { planet: 'S', _id: doc3._id });
+        assert.deepEqual(docs[2], { planet: 'C', _id: doc2._id });
+        assert.deepEqual(docs[3], { planet: 'R', _id: doc1._id });
+        assert.deepEqual(docs[4], { planet: 'Earth', _id: doc4._id });
+
+        cursor.projection({ age: 0, name: 0, _id: 0 });
+        cursor.exec(function (err, docs) {
+          assert.isNull(err);
+          docs.length.should.equal(5);
+          assert.deepEqual(docs[0], { planet: 'B' });
+          assert.deepEqual(docs[1], { planet: 'S' });
+          assert.deepEqual(docs[2], { planet: 'C' });
+          assert.deepEqual(docs[3], { planet: 'R' });
+          assert.deepEqual(docs[4], { planet: 'Earth' });
 
           done();
         });
       });
     });
 
+    it('Cannot use both modes except for _id', function (done) {
+      var cursor = new Cursor(d, {});
+      cursor.sort({ age: 1 });   // For easier finding
+      cursor.projection({ age: 1, name: 0 });
+      cursor.exec(function (err, docs) {
+        assert.isNotNull(err);
+        assert.isUndefined(docs);
+        done();
+      });
+    });
+
   });   // ==== End of 'Projections' ====
 
 });