Fix coercion from ObjectID to String

lib/dao.js

@@ -1135,12 +1135,7 @@ DataAccessObject._coerce = function (where) {
     }
     // Check there is an operator
     var operator = null;
-    if ('object' === typeof val) {
+    if (val.constructor === Object) {
-      if (Object.keys(val).length !== 1) {
-        // Skip if there are not only one properties
-        // as the assumption for operators is not true here
-        continue;
-      }
       for (var op in operators) {
         if (op in val) {
           val = val[op];
@@ -1182,7 +1177,7 @@ DataAccessObject._coerce = function (where) {
         }
       }
     } else {
-      if (val !== null && val !== undefined) {
+      if (val != null) {
         val = DataType(val);
       }
     }

test/loopback-dl.test.js

@@ -1269,6 +1269,18 @@ describe('DataAccessObject', function () {
     assert.deepEqual(where, {id: '1'});
     where = model._coerce({id: '1'});
     assert.deepEqual(where, {id: '1'});
+
+    // Mockup MongoDB ObjectID
+    function ObjectID(id) {
+      this.id = id;
+    }
+
+    ObjectID.prototype.toString = function() {
+      return this.id;
+    };
+
+    where = model._coerce({id: new ObjectID('1')});
+    assert.deepEqual(where, {id: '1'});
   });
 
   it('should be able to coerce where clause for number types', function () {