diff --git a/mongomap/__init__.py b/mongomap/__init__.py
index 1b7da2b3..eb72c30a 100644
--- a/mongomap/__init__.py
+++ b/mongomap/__init__.py
@@ -3,7 +3,38 @@ from document import *
 import fields
 from fields import *
 
-__all__ = document.__all__ + fields.__all__
+from pymongo import Connection
+
+__all__ = document.__all__ + fields.__all__ + ['connect']
 
 __author__ = 'Harry Marr'
 __version__ = '0.1'
+
+_connection_settings = {
+    'host': 'localhost',
+    'port': 27017,
+    'pool_size': 1,
+}
+_connection = None
+_db = None
+
+def _get_connection():
+    if _connection is None:
+        _connection = Connection(**_connection_settings)
+    return _connection
+
+def connect(db=None, username=None, password=None, **kwargs):
+    """Connect to the database specified by the 'db' argument. Connection 
+    settings may be provided here as well if the database is not running on
+    the default port on localhost. If authentication is needed, provide
+    username and password arguments as well.
+    """
+    if db is None:
+        raise TypeError('"db" argument must be provided to connect()')
+
+    _connection_settings.update(kwargs)
+    connection = _get_connection()
+    # Get DB from connection and auth if necessary
+    _db = connection[db]
+    if username is not None and password is not None:
+        _db.authenticate(username, password)
diff --git a/mongomap/base.py b/mongomap/base.py
index 3138e426..ddae4615 100644
--- a/mongomap/base.py
+++ b/mongomap/base.py
@@ -24,12 +24,13 @@ class BaseField(object):
 
         # Get value from document instance if available, if not use default
         value = instance._data.get(self.name)
-        if value is not None:
-            value = self._to_python(value)
-        elif self.default is not None:
-            value = self.default
-            if callable(value):
-                value = value()
+        if value is None:
+            if self.default is not None:
+                value = self.default
+                if callable(value):
+                    value = value()
+            else:
+                raise AttributeError(self.name)
         return value
 
     def __set__(self, instance, value):
@@ -40,7 +41,6 @@ class BaseField(object):
             try:
                 value = self._to_python(value)
                 self._validate(value)
-                value = self._to_mongo(value)
             except ValueError:
                 raise ValidationError('Invalid value for field of type "' +
                                       self.__class__.__name__ + '"')
@@ -61,7 +61,7 @@ class BaseField(object):
     def _validate(self, value):
         """Perform validation on a value.
         """
-        return value
+        pass
 
 
 class DocumentMetaclass(type):
@@ -143,7 +143,7 @@ class BaseDocument(object):
                 if attr_value.required:
                     raise ValidationError('Field "%s" is required' % self.name)
                 # Use default value
-                setattr(self, attr_name, getattr(self, attr_name))
+                setattr(self, attr_name, getattr(self, attr_name, None))
 
     def __iter__(self):
         # Use _data rather than _fields as iterator only looks at names so
@@ -161,11 +161,21 @@ class BaseDocument(object):
     def __setitem__(self, name, value):
         """Dictionary-style field access, set a field's value.
         """
-            # Ensure that the field exists before settings its value
+        # Ensure that the field exists before settings its value
         if name not in self._fields:
             raise KeyError(name)
         return setattr(self, name, value)
 
+    def __contains__(self, name):
+        try:
+            getattr(self, name)
+            return True
+        except AttributeError:
+            return False
+
+    def __len__(self):
+        return len(self._data)
+
     def _to_mongo(self):
         """Return data dictionary ready for use with MongoDB.
         """
diff --git a/tests/document.py b/tests/document.py
index 862cbe97..177560f1 100644
--- a/tests/document.py
+++ b/tests/document.py
@@ -61,6 +61,13 @@ class DocumentTest(unittest.TestCase):
         person['name'] = 'Another User'
         self.assertEquals(person['name'], 'Another User')
 
+        self.assertEquals(len(person), 2)
+
+        self.assertTrue('age' in person)
+        person.age = None
+        self.assertFalse('age' in person)
+        self.assertFalse('nationality' in person)
+
     def test_embedded_document(self):
         """Ensure that embedded documents are set up correctly.
         """