Fix bug whereby it is not possible to iterate over an empty Lmdb data…

…base

featureflow/__init__.py

@@ -1,4 +1,4 @@
-__version__ = '0.5.2'
+__version__ = '0.5.3'
 
 from model import BaseModel
 

featureflow/lmdbstore.py

@@ -120,7 +120,11 @@ def size(self, key):
         return len(buf)
 
     def iter_ids(self):
-        db = self.dbs.values()[0]
+        try:
+            db = self.dbs.values()[0]
+        except IndexError:
+            return
+
         with self.env.begin() as txn:
             cursor = txn.cursor(db)
             for _id in cursor.iternext(keys=True, values=False):

featureflow/test_lmdbstore.py

@@ -15,32 +15,44 @@ def setUp(self):
                 key_builder=self.key_builder)
         self.value = os.urandom(1000)
         self.key = self.key_builder.build('id', 'feature')
-        with self.db.write_stream(self.key, 'application/octet-stream') as ws:
-            ws.write(self.value)
 
     def tearDown(self):
         shutil.rmtree(self.path, ignore_errors=True)
 
+    def write_key(self):
+        with self.db.write_stream(self.key, 'application/octet-stream') as ws:
+            ws.write(self.value)
+
     def test_can_seek_to_beginning_of_value(self):
+        self.write_key()
         with self.db.read_stream(self.key) as rs:
             rs.read(100)
             rs.seek(0, os.SEEK_SET)
             self.assertEqual(0, rs.tell())
             self.assertEqual(rs.read(100), self.value[:100])
 
     def test_can_seek_relative_to_current_position(self):
+        self.write_key()
         with self.db.read_stream(self.key) as rs:
             rs.read(100)
             rs.seek(100, os.SEEK_CUR)
             self.assertEqual(200, rs.tell())
             self.assertEqual(rs.read(100), self.value[200:300])
 
     def test_can_seek_relative_to_end_of_value(self):
+        self.write_key()
         with self.db.read_stream(self.key) as rs:
             rs.seek(-100, os.SEEK_END)
             self.assertEqual(900, rs.tell())
             self.assertEqual(rs.read(100), self.value[-100:])
 
     def test_invalid_seek_argument_raises(self):
+        self.write_key()
         with self.db.read_stream(self.key) as rs:
             self.assertRaises(IOError, lambda: rs.seek(0, 999))
+
+    def test_can_iterate_over_empty_database(self):
+        _ids = list(self.db.iter_ids())
+        self.assertEqual(0, len(_ids))
+
+