Added MapField, similar to DictField

Similar to DictField except the value of each entry is always of a certain
(declared) field type.

Thanks again to @theojulienne for the code #108

mongoengine/fields.py

@@ -17,7 +17,7 @@ import warnings
 
 __all__ = ['StringField', 'IntField', 'FloatField', 'BooleanField',
            'DateTimeField', 'EmbeddedDocumentField', 'ListField', 'DictField',
-           'ObjectIdField', 'ReferenceField', 'ValidationError',
+           'ObjectIdField', 'ReferenceField', 'ValidationError', 'MapField',
            'DecimalField', 'URLField', 'GenericReferenceField', 'FileField',
            'BinaryField', 'SortedListField', 'EmailField', 'GeoPointField']
 
@@ -451,6 +451,97 @@ class DictField(BaseField):
     def lookup_member(self, member_name):
         return self.basecls(db_field=member_name)
 
+
+class MapField(BaseField):
+    """A field that maps a name to a specified field type. Similar to
+    a DictField, except the 'value' of each item must match the specified
+    field type.
+
+    .. versionadded:: 0.5
+    """
+
+    def __init__(self, field=None, *args, **kwargs):
+        if not isinstance(field, BaseField):
+            raise ValidationError('Argument to MapField constructor must be '
+                                  'a valid field')
+        self.field = field
+        kwargs.setdefault('default', lambda: {})
+        super(MapField, self).__init__(*args, **kwargs)
+
+    def validate(self, value):
+        """Make sure that a list of valid fields is being used.
+        """
+        if not isinstance(value, dict):
+            raise ValidationError('Only dictionaries may be used in a '
+                                  'DictField')
+
+        if any(('.' in k or '$' in k) for k in value):
+            raise ValidationError('Invalid dictionary key name - keys may not '
+                                  'contain "." or "$" characters')
+
+        try:
+            [self.field.validate(item) for item in value.values()]
+        except Exception, err:
+            raise ValidationError('Invalid MapField item (%s)' % str(item))
+
+    def __get__(self, instance, owner):
+        """Descriptor to automatically dereference references.
+        """
+        if instance is None:
+            # Document class being used rather than a document object
+            return self
+
+        if isinstance(self.field, ReferenceField):
+            referenced_type = self.field.document_type
+            # Get value from document instance if available
+            value_dict = instance._data.get(self.name)
+            if value_dict:
+                deref_dict = []
+                for key,value in value_dict.iteritems():
+                    # Dereference DBRefs
+                    if isinstance(value, (pymongo.dbref.DBRef)):
+                        value = _get_db().dereference(value)
+                        deref_dict[key] = referenced_type._from_son(value)
+                    else:
+                        deref_dict[key] = value
+                instance._data[self.name] = deref_dict
+
+        if isinstance(self.field, GenericReferenceField):
+            value_dict = instance._data.get(self.name)
+            if value_dict:
+                deref_dict = []
+                for key,value in value_dict.iteritems():
+                    # Dereference DBRefs
+                    if isinstance(value, (dict, pymongo.son.SON)):
+                        deref_dict[key] = self.field.dereference(value)
+                    else:
+                        deref_dict[key] = value
+                instance._data[self.name] = deref_dict
+
+        return super(MapField, self).__get__(instance, owner)
+
+    def to_python(self, value):
+        return dict( [(key,self.field.to_python(item)) for key,item in value.iteritems()] )
+
+    def to_mongo(self, value):
+        return dict( [(key,self.field.to_mongo(item)) for key,item in value.iteritems()] )
+
+    def prepare_query_value(self, op, value):
+        return self.field.prepare_query_value(op, value)
+
+    def lookup_member(self, member_name):
+        return self.field.lookup_member(member_name)
+
+    def _set_owner_document(self, owner_document):
+        self.field.owner_document = owner_document
+        self._owner_document = owner_document
+
+    def _get_owner_document(self, owner_document):
+        self._owner_document = owner_document
+
+    owner_document = property(_get_owner_document, _set_owner_document)
+
+
 class ReferenceField(BaseField):
     """A reference to a document that will be automatically dereferenced on
     access (lazily).