diff --git a/lib/dao.js b/lib/dao.js
index cef7552d..d01cd468 100644
--- a/lib/dao.js
+++ b/lib/dao.js
@@ -1878,7 +1878,7 @@ DataAccessObject.prototype.setAttributes = function setAttributes(data) {
 };
 
 DataAccessObject.prototype.unsetAttribute = function unsetAttribute(name, nullify) {
-  if (nullify) {
+  if (nullify || this.constructor.definition.settings.persistUndefinedAsNull) {
     this[name] = this.__data[name] = null;
   } else {
     delete this[name];
diff --git a/lib/model-builder.js b/lib/model-builder.js
index 09694ac2..eeec2355 100644
--- a/lib/model-builder.js
+++ b/lib/model-builder.js
@@ -429,6 +429,12 @@ ModelBuilder.prototype.define = function defineClass(className, properties, sett
         } else if (typeof DataType === 'string') {
           DataType = modelBuilder.resolveType(DataType);
         }
+
+        var persistUndefinedAsNull = ModelClass.definition.settings.persistUndefinedAsNull;
+        if (value === undefined && persistUndefinedAsNull) {
+          value = null;
+        }
+
         if (ModelClass.setter[propertyName]) {
           ModelClass.setter[propertyName].call(this, value); // Try setter first
         } else {
diff --git a/lib/model.js b/lib/model.js
index b5be726c..417e9471 100644
--- a/lib/model.js
+++ b/lib/model.js
@@ -77,6 +77,8 @@ ModelBaseClass.prototype._initProperties = function (data, options) {
     strict = ctor.definition.settings.strict;
   }
 
+  var persistUndefinedAsNull = ctor.definition.settings.persistUndefinedAsNull;
+
   if (ctor.hideInternalProperties) {
     // Object.defineProperty() is expensive. We only try to make the internal
     // properties hidden (non-enumerable) if the model class has the
@@ -151,6 +153,11 @@ ModelBaseClass.prototype._initProperties = function (data, options) {
     if (typeof propVal === 'function') {
       continue;
     }
+
+    if (propVal === undefined && persistUndefinedAsNull) {
+      propVal = null;
+    }
+
     if (properties[p]) {
       // Managed property
       if (applySetters || properties[p].id) {
@@ -257,6 +264,10 @@ ModelBaseClass.prototype._initProperties = function (data, options) {
         self.__data[p] = propVal;
     }
 
+    if (propVal === undefined && persistUndefinedAsNull) {
+      self.__data[p] = propVal = null;
+    }
+
     // Handle complex types (JSON/Object)
     if (!BASE_TYPES[type.name]) {
 
@@ -345,6 +356,7 @@ ModelBaseClass.prototype.toObject = function (onlySchema, removeHidden, removePr
 
   var strict = this.__strict;
   var schemaLess = (strict === false) || !onlySchema;
+  var persistUndefinedAsNull = Model.definition.settings.persistUndefinedAsNull;
 
   var props = Model.definition.properties;
   var keys = Object.keys(props);
@@ -373,6 +385,9 @@ ModelBaseClass.prototype.toObject = function (onlySchema, removeHidden, removePr
       if (val !== undefined && val !== null && val.toObject) {
         data[propertyName] = val.toObject(!schemaLess, removeHidden, true);
       } else {
+        if (val === undefined && persistUndefinedAsNull) {
+          val = null;
+        }
         data[propertyName] = val;
       }
     }
@@ -398,8 +413,11 @@ ModelBaseClass.prototype.toObject = function (onlySchema, removeHidden, removePr
       if (removeProtected && Model.isProtectedProperty(propertyName)) {
         continue;
       }
+      if (data[propertyName] !== undefined) {
+        continue;
+      }
       val = self[propertyName];
-      if (val !== undefined && data[propertyName] === undefined) {
+      if (val !== undefined) {
         if (typeof val === 'function') {
           continue;
         }
@@ -408,6 +426,8 @@ ModelBaseClass.prototype.toObject = function (onlySchema, removeHidden, removePr
         } else {
           data[propertyName] = val;
         }
+      } else if (persistUndefinedAsNull) {
+        data[propertyName] = null;
       }
     }
     // Now continue to check __data
@@ -434,6 +454,8 @@ ModelBaseClass.prototype.toObject = function (onlySchema, removeHidden, removePr
 
         if (val !== undefined && val !== null && val.toObject) {
           data[propertyName] = val.toObject(!schemaLess, removeHidden, true);
+        } else if (val === undefined && persistUndefinedAsNull) {
+          data[propertyName] = null;
         } else {
           data[propertyName] = val;
         }
diff --git a/test/datatype.test.js b/test/datatype.test.js
index 8b2c550f..bd61abc3 100644
--- a/test/datatype.test.js
+++ b/test/datatype.test.js
@@ -149,4 +149,102 @@ describe('datatypes', function () {
       coerced.nested.constructor.name.should.equal('Object');
   });
 
+  describe('model option persistUndefinedAsNull', function() {
+    var TestModel;
+    before(function(done) {
+      TestModel = db.define(
+        'TestModel',
+        {
+          desc: { type: String, required: false },
+          stars: { type: Number, required: false }
+        },
+        {
+          persistUndefinedAsNull: true
+        });
+
+      db.automigrate(done);
+    });
+
+    it('should set missing optional properties to null', function(done) {
+      var EXPECTED = { desc: null, stars: null };
+      TestModel.create({ name: 'a-test-name' }, function(err, created) {
+        if (err) return done(err);
+        created.should.have.properties(EXPECTED);
+
+        TestModel.findById(created.id, function(err, found) {
+          if (err) return done(err);
+          found.should.have.properties(EXPECTED);
+          done();
+        });
+      });
+    });
+
+    it('should convert property value undefined to null', function(done) {
+      var EXPECTED = { desc: null, extra: null };
+      var data ={ desc: undefined, extra: undefined };
+      TestModel.create(data, function(err, created) {
+        if (err) return done(err);
+        created.should.have.properties(EXPECTED);
+
+        TestModel.findById(created.id, function(err, found) {
+          if (err) return done(err);
+          found.should.have.properties(EXPECTED);
+          done();
+        });
+      });
+    });
+
+    it('should convert undefined to null in the setter', function() {
+      var inst = new TestModel();
+      inst.desc = undefined;
+      inst.should.have.property('desc', null);
+      inst.toObject().should.have.property('desc', null);
+    });
+
+    it('should use null in unsetAttribute()', function() {
+      var inst = new TestModel();
+      inst.unsetAttribute('stars');
+      inst.should.have.property('stars', null);
+      inst.toObject().should.have.property('stars', null);
+    });
+
+    it('should convert undefined to null on save', function(done) {
+      var EXPECTED = { desc: null, stars: null, extra: null };
+      TestModel.create({}, function(err, created) {
+        if (err) return done(err);
+        created.desc = undefined; // Note: this is may be a no-op
+        created.unsetAttribute('stars');
+        created.extra = undefined;
+        created.__data.dx = undefined;
+
+        created.save(function(err, saved) {
+          if (err) return done(err);
+          created.should.have.properties(EXPECTED);
+
+          TestModel.dataSource.connector.all(
+            TestModel.modelName,
+            { where: { id: created.id } },
+            function(err, found) {
+              if (err) return done(err);
+              should.exist(found[0]);
+              found[0].should.have.properties(EXPECTED);
+              done();
+            }
+          );
+        });
+      });
+    });
+
+    it('should convert undefined to null in toObject()', function() {
+      var inst = new TestModel();
+      inst.desc = undefined; // Note: this may be a no-op
+      inst.unsetAttribute('stars');
+      inst.extra = undefined;
+      inst.__data.dx = undefined;
+
+      inst.toObject(false).should.have.properties({
+       desc: null, stars: null, extra: null, dx: null
+      });
+    });
+  });
 });