Raise a more specific error when the model already exists

featureflow/__init__.py

@@ -1,4 +1,4 @@
-__version__ = '1.17.14'
+__version__ = '1.18.14'
 
 from model import BaseModel
 

featureflow/model.py

@@ -46,6 +46,13 @@ class NoPersistenceSettingsError(Exception):
     pass
 
 
+class ModelExistsError(Exception):
+    """
+    Error raised when a model has already been computed and persisted
+    """
+    pass
+
+
 class BaseModel(object):
     __metaclass__ = MetaModel
 
@@ -95,8 +102,9 @@ def process(cls, raise_if_exists=False, **kwargs):
             feature_key = feature.feature_key(_id, cls)
             # check if that feature is already stored
             if feature_key in cls.database:
-                raise ValueError(
-                    '{_id} is already stored in the database'.format(**locals()))
+                raise ModelExistsError(
+                    '{_id} is already stored in the database'.format(
+                        **locals()))
 
         graph = cls._build_extractor(_id)
         graph.remove_dead_nodes(cls.features.itervalues())

featureflow/test_integration.py

@@ -8,7 +8,7 @@
 
 from extractor import NotEnoughData, Aggregator, Node, InvalidProcessMethod
 from iteratornode import IteratorNode
-from model import BaseModel, NoPersistenceSettingsError
+from model import BaseModel, NoPersistenceSettingsError, ModelExistsError
 from feature import Feature, JSONFeature, CompressedFeature
 from data import *
 from bytestream import ByteStream, ByteStreamFeature
@@ -804,7 +804,7 @@ class Document(BaseModel, settings):
 
         Document.process(stream='humpty', _id='blah', raise_if_exists=True)
         # processing the same id a second time should raise an error
-        self.assertRaises(ValueError, lambda: Document.process(
+        self.assertRaises(ModelExistsError, lambda: Document.process(
             stream='humpty', _id='blah', raise_if_exists=True))
 
     def test_can_have_multiple_producer_like_nodes(self):