Merge branch 'master' of github.com:MongoEngine/mongoengine into freyr_binaryfield_query_value_type

mongoengine/fields.py

@@ -5,7 +5,6 @@ import re
 import socket
 import time
 import uuid
-import warnings
 from operator import itemgetter
 
 from bson import Binary, DBRef, ObjectId, SON
@@ -25,13 +24,18 @@ try:
 except ImportError:
     Int64 = long
 
+
 from mongoengine.base import (BaseDocument, BaseField, ComplexBaseField,
-                              GeoJsonBaseField, ObjectIdField, get_document)
+                              GeoJsonBaseField, LazyReference, ObjectIdField,
+                              get_document)
+from mongoengine.base.utils import LazyRegexCompiler
+from mongoengine.common import _import_class
 from mongoengine.connection import DEFAULT_CONNECTION_NAME, get_db
 from mongoengine.document import Document, EmbeddedDocument
 from mongoengine.errors import DoesNotExist, InvalidQueryError, ValidationError
 from mongoengine.python_support import StringIO
-from mongoengine.queryset import DO_NOTHING, QuerySet
+from mongoengine.queryset import DO_NOTHING
+from mongoengine.queryset.base import BaseQuerySet
 
 try:
     from PIL import Image, ImageOps
@@ -39,13 +43,20 @@ except ImportError:
     Image = None
     ImageOps = None
 
+if six.PY3:
+    # Useless as long as 2to3 gets executed
+    # as it turns `long` into `int` blindly
+    long = int
+
+
 __all__ = (
     'StringField', 'URLField', 'EmailField', 'IntField', 'LongField',
-    'FloatField', 'DecimalField', 'BooleanField', 'DateTimeField',
+    'FloatField', 'DecimalField', 'BooleanField', 'DateTimeField', 'DateField',
     'ComplexDateTimeField', 'EmbeddedDocumentField', 'ObjectIdField',
     'GenericEmbeddedDocumentField', 'DynamicField', 'ListField',
     'SortedListField', 'EmbeddedDocumentListField', 'DictField',
     'MapField', 'ReferenceField', 'CachedReferenceField',
+    'LazyReferenceField', 'GenericLazyReferenceField',
     'GenericReferenceField', 'BinaryField', 'GridFSError', 'GridFSProxy',
     'FileField', 'ImageGridFsProxy', 'ImproperlyConfigured', 'ImageField',
     'GeoPointField', 'PointField', 'LineStringField', 'PolygonField',
@@ -120,9 +131,9 @@ class URLField(StringField):
     .. versionadded:: 0.3
     """
 
-    _URL_REGEX = re.compile(
+    _URL_REGEX = LazyRegexCompiler(
         r'^(?:[a-z0-9\.\-]*)://'  # scheme is validated separately
-        r'(?:(?:[A-Z0-9](?:[A-Z0-9-]{0,61}[A-Z0-9])?\.)+(?:[A-Z]{2,6}\.?|[A-Z0-9-]{2,}(?<!-)\.?)|'  # domain...
+        r'(?:(?:[A-Z0-9](?:[A-Z0-9-_]{0,61}[A-Z0-9])?\.)+(?:[A-Z]{2,6}\.?|[A-Z0-9-]{2,}(?<!-)\.?)|'  # domain...
         r'localhost|'  # localhost...
         r'\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}|'  # ...or ipv4
         r'\[?[A-F0-9]*:[A-F0-9:]+\]?)'  # ...or ipv6
@@ -130,8 +141,7 @@ class URLField(StringField):
         r'(?:/?|[/?]\S+)$', re.IGNORECASE)
     _URL_SCHEMES = ['http', 'https', 'ftp', 'ftps']
 
-    def __init__(self, verify_exists=False, url_regex=None, schemes=None, **kwargs):
-        self.verify_exists = verify_exists
+    def __init__(self, url_regex=None, schemes=None, **kwargs):
         self.url_regex = url_regex or self._URL_REGEX
         self.schemes = schemes or self._URL_SCHEMES
         super(URLField, self).__init__(**kwargs)
@@ -154,7 +164,7 @@ class EmailField(StringField):
 
     .. versionadded:: 0.4
     """
-    USER_REGEX = re.compile(
+    USER_REGEX = LazyRegexCompiler(
         # `dot-atom` defined in RFC 5322 Section 3.2.3.
         r"(^[-!#$%&'*+/=?^_`{}|~0-9A-Z]+(\.[-!#$%&'*+/=?^_`{}|~0-9A-Z]+)*\Z"
         # `quoted-string` defined in RFC 5322 Section 3.2.4.
@@ -162,7 +172,7 @@ class EmailField(StringField):
         re.IGNORECASE
     )
 
-    UTF8_USER_REGEX = re.compile(
+    UTF8_USER_REGEX = LazyRegexCompiler(
         six.u(
             # RFC 6531 Section 3.3 extends `atext` (used by dot-atom) to
             # include `UTF8-non-ascii`.
@@ -172,7 +182,7 @@ class EmailField(StringField):
         ), re.IGNORECASE | re.UNICODE
     )
 
-    DOMAIN_REGEX = re.compile(
+    DOMAIN_REGEX = LazyRegexCompiler(
         r'((?:[A-Z0-9](?:[A-Z0-9-]{0,61}[A-Z0-9])?\.)+)(?:[A-Z0-9-]{2,63}(?<!-))\Z',
         re.IGNORECASE
     )
@@ -264,14 +274,14 @@ class IntField(BaseField):
     def to_python(self, value):
         try:
             value = int(value)
-        except ValueError:
+        except (TypeError, ValueError):
             pass
         return value
 
     def validate(self, value):
         try:
             value = int(value)
-        except Exception:
+        except (TypeError, ValueError):
             self.error('%s could not be converted to int' % value)
 
         if self.min_value is not None and value < self.min_value:
@@ -297,7 +307,7 @@ class LongField(BaseField):
     def to_python(self, value):
         try:
             value = long(value)
-        except ValueError:
+        except (TypeError, ValueError):
             pass
         return value
 
@@ -307,7 +317,7 @@ class LongField(BaseField):
     def validate(self, value):
         try:
             value = long(value)
-        except Exception:
+        except (TypeError, ValueError):
             self.error('%s could not be converted to long' % value)
 
         if self.min_value is not None and value < self.min_value:
@@ -361,7 +371,8 @@ class FloatField(BaseField):
 
 
 class DecimalField(BaseField):
-    """Fixed-point decimal number field.
+    """Fixed-point decimal number field. Stores the value as a float by default unless `force_string` is used.
+    If using floats, beware of Decimal to float conversion (potential precision loss)
 
     .. versionchanged:: 0.8
     .. versionadded:: 0.3
@@ -372,7 +383,9 @@ class DecimalField(BaseField):
         """
         :param min_value: Validation rule for the minimum acceptable value.
         :param max_value: Validation rule for the maximum acceptable value.
-        :param force_string: Store as a string.
+        :param force_string: Store the value as a string (instead of a float).
+         Be aware that this affects query sorting and operation like lte, gte (as string comparison is applied)
+         and some query operator won't work (e.g: inc, dec)
         :param precision: Number of decimal places to store.
         :param rounding: The rounding rule from the python decimal library:
 
@@ -403,7 +416,7 @@ class DecimalField(BaseField):
         # Convert to string for python 2.6 before casting to Decimal
         try:
             value = decimal.Decimal('%s' % value)
-        except decimal.InvalidOperation:
+        except (TypeError, ValueError, decimal.InvalidOperation):
             return value
         return value.quantize(decimal.Decimal('.%s' % ('0' * self.precision)), rounding=self.rounding)
 
@@ -420,7 +433,7 @@ class DecimalField(BaseField):
                 value = six.text_type(value)
             try:
                 value = decimal.Decimal(value)
-            except Exception as exc:
+            except (TypeError, ValueError, decimal.InvalidOperation) as exc:
                 self.error('Could not convert value to decimal: %s' % exc)
 
         if self.min_value is not None and value < self.min_value:
@@ -459,6 +472,8 @@ class DateTimeField(BaseField):
     installed you can utilise it to convert varying types of date formats into valid
     python datetime objects.
 
+    Note: To default the field to the current datetime, use: DateTimeField(default=datetime.utcnow)
+
     Note: Microseconds are rounded to the nearest millisecond.
       Pre UTC microsecond support is effectively broken.
       Use :class:`~mongoengine.fields.ComplexDateTimeField` if you
@@ -522,6 +537,22 @@ class DateTimeField(BaseField):
         return super(DateTimeField, self).prepare_query_value(op, self.to_mongo(value))
 
 
+class DateField(DateTimeField):
+    def to_mongo(self, value):
+        value = super(DateField, self).to_mongo(value)
+        # drop hours, minutes, seconds
+        if isinstance(value, datetime.datetime):
+            value = datetime.datetime(value.year, value.month, value.day)
+        return value
+
+    def to_python(self, value):
+        value = super(DateField, self).to_python(value)
+        # convert datetime to date
+        if isinstance(value, datetime.datetime):
+            value = datetime.date(value.year, value.month, value.day)
+        return value
+
+
 class ComplexDateTimeField(StringField):
     """
     ComplexDateTimeField handles microseconds exactly instead of rounding
@@ -538,11 +569,15 @@ class ComplexDateTimeField(StringField):
     The `,` as the separator can be easily modified by passing the `separator`
     keyword when initializing the field.
 
+    Note: To default the field to the current datetime, use: DateTimeField(default=datetime.utcnow)
+
     .. versionadded:: 0.5
     """
 
     def __init__(self, separator=',', **kwargs):
-        self.names = ['year', 'month', 'day', 'hour', 'minute', 'second', 'microsecond']
+        """
+        :param separator: Allows to customize the separator used for storage (default ``,``)
+        """
         self.separator = separator
         self.format = separator.join(['%Y', '%m', '%d', '%H', '%M', '%S', '%f'])
         super(ComplexDateTimeField, self).__init__(**kwargs)
@@ -569,20 +604,24 @@ class ComplexDateTimeField(StringField):
         >>> ComplexDateTimeField()._convert_from_string(a)
         datetime.datetime(2011, 6, 8, 20, 26, 24, 92284)
         """
-        values = map(int, data.split(self.separator))
+        values = [int(d) for d in data.split(self.separator)]
         return datetime.datetime(*values)
 
     def __get__(self, instance, owner):
+        if instance is None:
+            return self
+
         data = super(ComplexDateTimeField, self).__get__(instance, owner)
-        if data is None:
-            return None if self.null else datetime.datetime.now()
-        if isinstance(data, datetime.datetime):
+
+        if isinstance(data, datetime.datetime) or data is None:
             return data
         return self._convert_from_string(data)
 
     def __set__(self, instance, value):
-        value = self._convert_from_datetime(value) if value else value
-        return super(ComplexDateTimeField, self).__set__(instance, value)
+        super(ComplexDateTimeField, self).__set__(instance, value)
+        value = instance._data[self.name]
+        if value is not None:
+            instance._data[self.name] = self._convert_from_datetime(value)
 
     def validate(self, value):
         value = self.to_python(value)
@@ -611,6 +650,7 @@ class EmbeddedDocumentField(BaseField):
     """
 
     def __init__(self, document_type, **kwargs):
+        # XXX ValidationError raised outside of the "validate" method.
         if not (
             isinstance(document_type, six.string_types) or
             issubclass(document_type, EmbeddedDocument)
@@ -625,9 +665,17 @@ class EmbeddedDocumentField(BaseField):
     def document_type(self):
         if isinstance(self.document_type_obj, six.string_types):
             if self.document_type_obj == RECURSIVE_REFERENCE_CONSTANT:
-                self.document_type_obj = self.owner_document
+                resolved_document_type = self.owner_document
             else:
-                self.document_type_obj = get_document(self.document_type_obj)
+                resolved_document_type = get_document(self.document_type_obj)
+
+            if not issubclass(resolved_document_type, EmbeddedDocument):
+                # Due to the late resolution of the document_type
+                # There is a chance that it won't be an EmbeddedDocument (#1661)
+                self.error('Invalid embedded document class provided to an '
+                           'EmbeddedDocumentField')
+            self.document_type_obj = resolved_document_type
+
         return self.document_type_obj
 
     def to_python(self, value):
@@ -686,16 +734,28 @@ class GenericEmbeddedDocumentField(BaseField):
         return value
 
     def validate(self, value, clean=True):
+        if self.choices and isinstance(value, SON):
+            for choice in self.choices:
+                if value['_cls'] == choice._class_name:
+                    return True
+
         if not isinstance(value, EmbeddedDocument):
             self.error('Invalid embedded document instance provided to an '
                        'GenericEmbeddedDocumentField')
 
         value.validate(clean=clean)
 
+    def lookup_member(self, member_name):
+        if self.choices:
+            for choice in self.choices:
+                field = choice._fields.get(member_name)
+                if field:
+                    return field
+        return None
+
     def to_mongo(self, document, use_db_field=True, fields=None):
         if document is None:
             return None
-
         data = document.to_mongo(use_db_field, fields)
         if '_cls' not in data:
             data['_cls'] = document._class_name
@@ -779,10 +839,20 @@ class ListField(ComplexBaseField):
         kwargs.setdefault('default', lambda: [])
         super(ListField, self).__init__(**kwargs)
 
+    def __get__(self, instance, owner):
+        if instance is None:
+            # Document class being used rather than a document object
+            return self
+        value = instance._data.get(self.name)
+        LazyReferenceField = _import_class('LazyReferenceField')
+        GenericLazyReferenceField = _import_class('GenericLazyReferenceField')
+        if isinstance(self.field, (LazyReferenceField, GenericLazyReferenceField)) and value:
+            instance._data[self.name] = [self.field.build_lazyref(x) for x in value]
+        return super(ListField, self).__get__(instance, owner)
+
     def validate(self, value):
         """Make sure that a list of valid fields is being used."""
-        if (not isinstance(value, (list, tuple, QuerySet)) or
-                isinstance(value, six.string_types)):
+        if not isinstance(value, (list, tuple, BaseQuerySet)):
             self.error('Only lists and tuples may be used in a list field')
         super(ListField, self).validate(value)
 
@@ -874,7 +944,7 @@ def key_has_dot_or_dollar(d):
     dictionary contains a dot or a dollar sign.
     """
     for k, v in d.items():
-        if ('.' in k or '$' in k) or (isinstance(v, dict) and key_has_dot_or_dollar(v)):
+        if ('.' in k or k.startswith('$')) or (isinstance(v, dict) and key_has_dot_or_dollar(v)):
             return True
 
 
@@ -889,12 +959,10 @@ class DictField(ComplexBaseField):
     .. versionchanged:: 0.5 - Can now handle complex / varying types of data
     """
 
-    def __init__(self, basecls=None, field=None, *args, **kwargs):
+    def __init__(self, field=None, *args, **kwargs):
         self.field = field
         self._auto_dereference = False
-        self.basecls = basecls or BaseField
-        if not issubclass(self.basecls, BaseField):
-            self.error('DictField only accepts dict values')
+
         kwargs.setdefault('default', lambda: {})
         super(DictField, self).__init__(*args, **kwargs)
 
@@ -909,11 +977,11 @@ class DictField(ComplexBaseField):
             self.error(msg)
         if key_has_dot_or_dollar(value):
             self.error('Invalid dictionary key name - keys may not contain "."'
-                       ' or "$" characters')
+                       ' or startswith "$" characters')
         super(DictField, self).validate(value)
 
     def lookup_member(self, member_name):
-        return DictField(basecls=self.basecls, db_field=member_name)
+        return DictField(db_field=member_name)
 
     def prepare_query_value(self, op, value):
         match_operators = ['contains', 'icontains', 'startswith',
@@ -923,7 +991,7 @@ class DictField(ComplexBaseField):
         if op in match_operators and isinstance(value, six.string_types):
             return StringField().prepare_query_value(op, value)
 
-        if hasattr(self.field, 'field'):
+        if hasattr(self.field, 'field'):    # Used for instance when using DictField(ListField(IntField()))
             if op in ('set', 'unset') and isinstance(value, dict):
                 return {
                     k: self.field.prepare_query_value(op, v)
@@ -943,6 +1011,7 @@ class MapField(DictField):
     """
 
     def __init__(self, field=None, *args, **kwargs):
+        # XXX ValidationError raised outside of the "validate" method.
         if not isinstance(field, BaseField):
             self.error('Argument to MapField constructor must be a valid '
                        'field')
@@ -953,6 +1022,15 @@ class ReferenceField(BaseField):
     """A reference to a document that will be automatically dereferenced on
     access (lazily).
 
+    Note this means you will get a database I/O access everytime you access
+    this field. This is necessary because the field returns a :class:`~mongoengine.Document`
+    which precise type can depend of the value of the `_cls` field present in the
+    document in database.
+    In short, using this type of field can lead to poor performances (especially
+    if you access this field only to retrieve it `pk` field which is already
+    known before dereference). To solve this you should consider using the
+    :class:`~mongoengine.fields.LazyReferenceField`.
+
     Use the `reverse_delete_rule` to handle what should happen if the document
     the field is referencing is deleted.  EmbeddedDocuments, DictFields and
     MapFields does not support reverse_delete_rule and an `InvalidDocumentError`
@@ -971,11 +1049,13 @@ class ReferenceField(BaseField):
 
     .. code-block:: python
 
-        class Bar(Document):
-            content = StringField()
-            foo = ReferenceField('Foo')
+        class Org(Document):
+            owner = ReferenceField('User')
 
-        Foo.register_delete_rule(Bar, 'foo', NULLIFY)
+        class User(Document):
+            org = ReferenceField('Org', reverse_delete_rule=CASCADE)
+
+        User.register_delete_rule(Org, 'owner', DENY)
 
     .. versionchanged:: 0.5 added `reverse_delete_rule`
     """
@@ -993,6 +1073,7 @@ class ReferenceField(BaseField):
             A reference to an abstract document type is always stored as a
             :class:`~pymongo.dbref.DBRef`, regardless of the value of `dbref`.
         """
+        # XXX ValidationError raised outside of the "validate" method.
         if (
             not isinstance(document_type, six.string_types) and
             not issubclass(document_type, Document)
@@ -1022,9 +1103,9 @@ class ReferenceField(BaseField):
 
         # Get value from document instance if available
         value = instance._data.get(self.name)
-        self._auto_dereference = instance._fields[self.name]._auto_dereference
+        auto_dereference = instance._fields[self.name]._auto_dereference
         # Dereference DBRefs
-        if self._auto_dereference and isinstance(value, DBRef):
+        if auto_dereference and isinstance(value, DBRef):
             if hasattr(value, 'cls'):
                 # Dereference using the class type specified in the reference
                 cls = get_document(value.cls)
@@ -1047,6 +1128,8 @@ class ReferenceField(BaseField):
         if isinstance(document, Document):
             # We need the id from the saved object to create the DBRef
             id_ = document.pk
+
+            # XXX ValidationError raised outside of the "validate" method.
             if id_ is None:
                 self.error('You can only reference documents once they have'
                            ' been saved to the database')
@@ -1086,21 +1169,13 @@ class ReferenceField(BaseField):
         return self.to_mongo(value)
 
     def validate(self, value):
-
-        if not isinstance(value, (self.document_type, DBRef, ObjectId)):
-            self.error('A ReferenceField only accepts DBRef, ObjectId or documents')
+        if not isinstance(value, (self.document_type, LazyReference, DBRef, ObjectId)):
+            self.error('A ReferenceField only accepts DBRef, LazyReference, ObjectId or documents')
 
         if isinstance(value, Document) and value.id is None:
             self.error('You can only reference documents once they have been '
                        'saved to the database')
 
-        if self.document_type._meta.get('abstract') and \
-                not isinstance(value, self.document_type):
-            self.error(
-                '%s is not an instance of abstract reference type %s' % (
-                    self.document_type._class_name)
-            )
-
     def lookup_member(self, member_name):
         return self.document_type._fields.get(member_name)
 
@@ -1121,6 +1196,7 @@ class CachedReferenceField(BaseField):
         if fields is None:
             fields = []
 
+        # XXX ValidationError raised outside of the "validate" method.
         if (
             not isinstance(document_type, six.string_types) and
             not issubclass(document_type, Document)
@@ -1180,9 +1256,10 @@ class CachedReferenceField(BaseField):
 
         # Get value from document instance if available
         value = instance._data.get(self.name)
-        self._auto_dereference = instance._fields[self.name]._auto_dereference
+        auto_dereference = instance._fields[self.name]._auto_dereference
+
         # Dereference DBRefs
-        if self._auto_dereference and isinstance(value, DBRef):
+        if auto_dereference and isinstance(value, DBRef):
             dereferenced = self.document_type._get_db().dereference(value)
             if dereferenced is None:
                 raise DoesNotExist('Trying to dereference unknown document %s' % value)
@@ -1195,6 +1272,7 @@ class CachedReferenceField(BaseField):
         id_field_name = self.document_type._meta['id_field']
         id_field = self.document_type._fields[id_field_name]
 
+        # XXX ValidationError raised outside of the "validate" method.
         if isinstance(document, Document):
             # We need the id from the saved object to create the DBRef
             id_ = document.pk
@@ -1203,7 +1281,6 @@ class CachedReferenceField(BaseField):
                            ' been saved to the database')
         else:
             self.error('Only accept a document object')
-            # TODO: should raise here or will fail next statement
 
         value = SON((
             ('_id', id_field.to_mongo(id_)),
@@ -1221,16 +1298,20 @@ class CachedReferenceField(BaseField):
         if value is None:
             return None
 
+        # XXX ValidationError raised outside of the "validate" method.
         if isinstance(value, Document):
             if value.pk is None:
                 self.error('You can only reference documents once they have'
                            ' been saved to the database')
-            return {'_id': value.pk}
+            value_dict = {'_id': value.pk}
+            for field in self.fields:
+                value_dict.update({field: value[field]})
+
+            return value_dict
 
         raise NotImplementedError
 
     def validate(self, value):
-
         if not isinstance(value, self.document_type):
             self.error('A CachedReferenceField only accepts documents')
 
@@ -1263,6 +1344,12 @@ class GenericReferenceField(BaseField):
     """A reference to *any* :class:`~mongoengine.document.Document` subclass
     that will be automatically dereferenced on access (lazily).
 
+    Note this field works the same way as :class:`~mongoengine.document.ReferenceField`,
+    doing database I/O access the first time it is accessed (even if it's to access
+    it ``pk`` or ``id`` field).
+    To solve this you should consider using the
+    :class:`~mongoengine.fields.GenericLazyReferenceField`.
+
     .. note ::
         * Any documents used as a generic reference must be registered in the
           document registry.  Importing the model will automatically register
@@ -1285,6 +1372,8 @@ class GenericReferenceField(BaseField):
                 elif isinstance(choice, type) and issubclass(choice, Document):
                     self.choices.append(choice._class_name)
                 else:
+                    # XXX ValidationError raised outside of the "validate"
+                    # method.
                     self.error('Invalid choices provided: must be a list of'
                                'Document subclasses and/or six.string_typess')
 
@@ -1303,8 +1392,8 @@ class GenericReferenceField(BaseField):
 
         value = instance._data.get(self.name)
 
-        self._auto_dereference = instance._fields[self.name]._auto_dereference
-        if self._auto_dereference and isinstance(value, (dict, SON)):
+        auto_dereference = instance._fields[self.name]._auto_dereference
+        if auto_dereference and isinstance(value, (dict, SON)):
             dereferenced = self.dereference(value)
             if dereferenced is None:
                 raise DoesNotExist('Trying to dereference unknown document %s' % value)
@@ -1348,6 +1437,7 @@ class GenericReferenceField(BaseField):
             # We need the id from the saved object to create the DBRef
             id_ = document.id
             if id_ is None:
+                # XXX ValidationError raised outside of the "validate" method.
                 self.error('You can only reference documents once they have'
                            ' been saved to the database')
         else:
@@ -1385,10 +1475,10 @@ class BinaryField(BaseField):
         return Binary(value)
 
     def validate(self, value):
-        if not isinstance(value, (six.binary_type, six.text_type, Binary)):
+        if not isinstance(value, (six.binary_type, Binary)):
             self.error('BinaryField only accepts instances of '
                        '(%s, %s, Binary)' % (
-                           six.binary_type.__name__, six.text_type.__name__))
+                           six.binary_type.__name__, Binary.__name__))
 
         if self.max_bytes is not None and len(value) > self.max_bytes:
             self.error('Binary value is too long')
@@ -1439,9 +1529,11 @@ class GridFSProxy(object):
     def __get__(self, instance, value):
         return self
 
-    def __nonzero__(self):
+    def __bool__(self):
         return bool(self.grid_id)
 
+    __nonzero__ = __bool__  # For Py2 support
+
     def __getstate__(self):
         self_dict = self.__dict__
         self_dict['_fs'] = None
@@ -1459,9 +1551,9 @@ class GridFSProxy(object):
         return '<%s: %s>' % (self.__class__.__name__, self.grid_id)
 
     def __str__(self):
-        name = getattr(
-            self.get(), 'filename', self.grid_id) if self.get() else '(no file)'
-        return '<%s: %s>' % (self.__class__.__name__, name)
+        gridout = self.get()
+        filename = getattr(gridout, 'filename') if gridout else '<no file>'
+        return '<%s: %s (%s)>' % (self.__class__.__name__, filename, self.grid_id)
 
     def __eq__(self, other):
         if isinstance(other, GridFSProxy):
@@ -1471,6 +1563,9 @@ class GridFSProxy(object):
         else:
             return False
 
+    def __ne__(self, other):
+        return not self == other
+
     @property
     def fs(self):
         if not self._fs:
@@ -1778,12 +1873,9 @@ class ImageField(FileField):
     """
     A Image File storage field.
 
-    @size (width, height, force):
-        max size to store images, if larger will be automatically resized
-        ex: size=(800, 600, True)
-
-    @thumbnail (width, height, force):
-        size to generate a thumbnail
+    :param size: max size to store images, provided as (width, height, force)
+        if larger, it will be automatically resized (ex: size=(800, 600, True))
+    :param thumbnail_size: size to generate a thumbnail, provided as (width, height, force)
 
     .. versionadded:: 0.6
     """
@@ -1854,8 +1946,7 @@ class SequenceField(BaseField):
         self.collection_name = collection_name or self.COLLECTION_NAME
         self.db_alias = db_alias or DEFAULT_CONNECTION_NAME
         self.sequence_name = sequence_name
-        self.value_decorator = (callable(value_decorator) and
-                                value_decorator or self.VALUE_DECORATOR)
+        self.value_decorator = value_decorator if callable(value_decorator) else self.VALUE_DECORATOR
         super(SequenceField, self).__init__(*args, **kwargs)
 
     def generate(self):
@@ -1964,7 +2055,7 @@ class UUIDField(BaseField):
                 if not isinstance(value, six.string_types):
                     value = six.text_type(value)
                 return uuid.UUID(value)
-            except Exception:
+            except (ValueError, TypeError, AttributeError):
                 return original_value
         return value
 
@@ -1986,7 +2077,7 @@ class UUIDField(BaseField):
                 value = str(value)
             try:
                 uuid.UUID(value)
-            except Exception as exc:
+            except (ValueError, TypeError, AttributeError) as exc:
                 self.error('Could not convert to UUID: %s' % exc)
 
 
@@ -2144,3 +2235,201 @@ class MultiPolygonField(GeoJsonBaseField):
     .. versionadded:: 0.9
     """
     _type = 'MultiPolygon'
+
+
+class LazyReferenceField(BaseField):
+    """A really lazy reference to a document.
+    Unlike the :class:`~mongoengine.fields.ReferenceField` it will
+    **not** be automatically (lazily) dereferenced on access.
+    Instead, access will return a :class:`~mongoengine.base.LazyReference` class
+    instance, allowing access to `pk` or manual dereference by using
+    ``fetch()`` method.
+
+    .. versionadded:: 0.15
+    """
+
+    def __init__(self, document_type, passthrough=False, dbref=False,
+                 reverse_delete_rule=DO_NOTHING, **kwargs):
+        """Initialises the Reference Field.
+
+        :param dbref:  Store the reference as :class:`~pymongo.dbref.DBRef`
+          or as the :class:`~pymongo.objectid.ObjectId`.id .
+        :param reverse_delete_rule: Determines what to do when the referring
+          object is deleted
+        :param passthrough: When trying to access unknown fields, the
+          :class:`~mongoengine.base.datastructure.LazyReference` instance will
+          automatically call `fetch()` and try to retrive the field on the fetched
+          document. Note this only work getting field (not setting or deleting).
+        """
+        # XXX ValidationError raised outside of the "validate" method.
+        if (
+            not isinstance(document_type, six.string_types) and
+            not issubclass(document_type, Document)
+        ):
+            self.error('Argument to LazyReferenceField constructor must be a '
+                       'document class or a string')
+
+        self.dbref = dbref
+        self.passthrough = passthrough
+        self.document_type_obj = document_type
+        self.reverse_delete_rule = reverse_delete_rule
+        super(LazyReferenceField, self).__init__(**kwargs)
+
+    @property
+    def document_type(self):
+        if isinstance(self.document_type_obj, six.string_types):
+            if self.document_type_obj == RECURSIVE_REFERENCE_CONSTANT:
+                self.document_type_obj = self.owner_document
+            else:
+                self.document_type_obj = get_document(self.document_type_obj)
+        return self.document_type_obj
+
+    def build_lazyref(self, value):
+        if isinstance(value, LazyReference):
+            if value.passthrough != self.passthrough:
+                value = LazyReference(value.document_type, value.pk, passthrough=self.passthrough)
+        elif value is not None:
+            if isinstance(value, self.document_type):
+                value = LazyReference(self.document_type, value.pk, passthrough=self.passthrough)
+            elif isinstance(value, DBRef):
+                value = LazyReference(self.document_type, value.id, passthrough=self.passthrough)
+            else:
+                # value is the primary key of the referenced document
+                value = LazyReference(self.document_type, value, passthrough=self.passthrough)
+        return value
+
+    def __get__(self, instance, owner):
+        """Descriptor to allow lazy dereferencing."""
+        if instance is None:
+            # Document class being used rather than a document object
+            return self
+
+        value = self.build_lazyref(instance._data.get(self.name))
+        if value:
+            instance._data[self.name] = value
+
+        return super(LazyReferenceField, self).__get__(instance, owner)
+
+    def to_mongo(self, value):
+        if isinstance(value, LazyReference):
+            pk = value.pk
+        elif isinstance(value, self.document_type):
+            pk = value.pk
+        elif isinstance(value, DBRef):
+            pk = value.id
+        else:
+            # value is the primary key of the referenced document
+            pk = value
+        id_field_name = self.document_type._meta['id_field']
+        id_field = self.document_type._fields[id_field_name]
+        pk = id_field.to_mongo(pk)
+        if self.dbref:
+            return DBRef(self.document_type._get_collection_name(), pk)
+        else:
+            return pk
+
+    def validate(self, value):
+        if isinstance(value, LazyReference):
+            if value.collection != self.document_type._get_collection_name():
+                self.error('Reference must be on a `%s` document.' % self.document_type)
+            pk = value.pk
+        elif isinstance(value, self.document_type):
+            pk = value.pk
+        elif isinstance(value, DBRef):
+            # TODO: check collection ?
+            collection = self.document_type._get_collection_name()
+            if value.collection != collection:
+                self.error("DBRef on bad collection (must be on `%s`)" % collection)
+            pk = value.id
+        else:
+            # value is the primary key of the referenced document
+            id_field_name = self.document_type._meta['id_field']
+            id_field = getattr(self.document_type, id_field_name)
+            pk = value
+            try:
+                id_field.validate(pk)
+            except ValidationError:
+                self.error(
+                    "value should be `{0}` document, LazyReference or DBRef on `{0}` "
+                    "or `{0}`'s primary key (i.e. `{1}`)".format(
+                        self.document_type.__name__, type(id_field).__name__))
+
+        if pk is None:
+            self.error('You can only reference documents once they have been '
+                       'saved to the database')
+
+    def prepare_query_value(self, op, value):
+        if value is None:
+            return None
+        super(LazyReferenceField, self).prepare_query_value(op, value)
+        return self.to_mongo(value)
+
+    def lookup_member(self, member_name):
+        return self.document_type._fields.get(member_name)
+
+
+class GenericLazyReferenceField(GenericReferenceField):
+    """A reference to *any* :class:`~mongoengine.document.Document` subclass.
+    Unlike the :class:`~mongoengine.fields.GenericReferenceField` it will
+    **not** be automatically (lazily) dereferenced on access.
+    Instead, access will return a :class:`~mongoengine.base.LazyReference` class
+    instance, allowing access to `pk` or manual dereference by using
+    ``fetch()`` method.
+
+    .. note ::
+        * Any documents used as a generic reference must be registered in the
+          document registry.  Importing the model will automatically register
+          it.
+
+        * You can use the choices param to limit the acceptable Document types
+
+    .. versionadded:: 0.15
+    """
+
+    def __init__(self, *args, **kwargs):
+        self.passthrough = kwargs.pop('passthrough', False)
+        super(GenericLazyReferenceField, self).__init__(*args, **kwargs)
+
+    def _validate_choices(self, value):
+        if isinstance(value, LazyReference):
+            value = value.document_type._class_name
+        super(GenericLazyReferenceField, self)._validate_choices(value)
+
+    def build_lazyref(self, value):
+        if isinstance(value, LazyReference):
+            if value.passthrough != self.passthrough:
+                value = LazyReference(value.document_type, value.pk, passthrough=self.passthrough)
+        elif value is not None:
+            if isinstance(value, (dict, SON)):
+                value = LazyReference(get_document(value['_cls']), value['_ref'].id, passthrough=self.passthrough)
+            elif isinstance(value, Document):
+                value = LazyReference(type(value), value.pk, passthrough=self.passthrough)
+        return value
+
+    def __get__(self, instance, owner):
+        if instance is None:
+            return self
+
+        value = self.build_lazyref(instance._data.get(self.name))
+        if value:
+            instance._data[self.name] = value
+
+        return super(GenericLazyReferenceField, self).__get__(instance, owner)
+
+    def validate(self, value):
+        if isinstance(value, LazyReference) and value.pk is None:
+            self.error('You can only reference documents once they have been'
+                       ' saved to the database')
+        return super(GenericLazyReferenceField, self).validate(value)
+
+    def to_mongo(self, document):
+        if document is None:
+            return None
+
+        if isinstance(document, LazyReference):
+            return SON((
+                ('_cls', document.document_type._class_name),
+                ('_ref', DBRef(document.document_type._get_collection_name(), document.pk))
+            ))
+        else:
+            return super(GenericLazyReferenceField, self).to_mongo(document)