fix-#515: sparse fields

docs/changelog.rst

@@ -5,6 +5,7 @@ Changelog
 
 Changes in 0.9.X - DEV
 ======================
+- Sparse fields #515
 - write_concern not in params of Collection#remove #801
 - Better BaseDocument equality check when not saved #798
 - OperationError: Shard Keys are immutable. Tried to update id even though the document is not yet saved #771

mongoengine/base/document.py

@@ -786,10 +786,9 @@ class BaseDocument(object):
         """
         unique_indexes = []
         for field_name, field in cls._fields.items():
-            sparse = False
+            sparse = field.sparse
             # Generate a list of indexes needed by uniqueness constraints
             if field.unique:
-                field.required = True
                 unique_fields = [field.db_field]
 
                 # Add any unique_with fields to the back of the index spec

mongoengine/base/fields.py

@@ -37,7 +37,7 @@ class BaseField(object):
     def __init__(self, db_field=None, name=None, required=False, default=None,
                  unique=False, unique_with=None, primary_key=False,
                  validation=None, choices=None, verbose_name=None,
-                 help_text=None, null=False):
+                 help_text=None, null=False, sparse=False):
         """
         :param db_field: The database field to store this field in
             (defaults to the name of the field)
@@ -62,6 +62,8 @@ class BaseField(object):
             used when generating model forms from the document model.
         :param null: (optional) Is the field value can be null. If no and there is a default value
             then the default value is set
+        :param sparse: (optional) `sparse=True` combined with `unique=True` and `required=False`
+            means that uniqueness won't be enforced for `None` values
         """
         self.db_field = (db_field or name) if not primary_key else '_id'
 
@@ -78,6 +80,7 @@ class BaseField(object):
         self.verbose_name = verbose_name
         self.help_text = help_text
         self.null = null
+        self.sparse = sparse
 
         # Adjust the appropriate creation counter, and save our local copy.
         if self.db_field == '_id':

tests/fields/fields.py

@@ -3057,6 +3057,15 @@ class FieldTest(unittest.TestCase):
         self.assertEquals(Animal.objects(_cls__in=["Animal.Mammal.Dog", "Animal.Fish"]).count(), 2)
         self.assertEquals(Animal.objects(_cls__in=["Animal.Fish.Guppy"]).count(), 0)
 
+    def test_sparse_field(self):
+        class Doc(Document):
+            name = StringField(required=False, unique=True, sparse=True)
+        try:
+            Doc().save()
+            Doc().save()
+        except Exception:
+            self.fail()
+
 
 if __name__ == '__main__':
     unittest.main()