fix bug when starting with new db file (#3)

affine/engine.py

@@ -1,3 +1,4 @@
+import os
 import pickle
 from abc import ABC, abstractmethod
 from collections import defaultdict
@@ -91,7 +92,7 @@ def __init__(
     ) -> None:  # maybe add option to the init for ANN algo
         self.path = path
         self.records: dict[str, list[Collection]] = defaultdict(list)
-        if self.path is not None:
+        if self.path is not None and os.path.exists(self.path):
             with open(self.path, "rb") as f:
                 self.records = pickle.load(f)
         self.collection_id_counter: dict[str, int] = defaultdict(

tests/test_engine.py

@@ -81,6 +81,17 @@ def test_local_engine(data: list[Collection]):
     assert db.insert(Product(name="Banana", price=2.0)) == 2
 
 
+def test_local_engine_persistence(data: list[Collection], tmp_path):
+    db = LocalEngine(tmp_path / "db.affine")
+
+    assert len(db.query(Person.objects())) == 0
+    for rec in data:
+        db.insert(rec)
+
+    db2 = LocalEngine(tmp_path / "db.affine")
+    assert len(db2.query(Person.objects())) == 2
+
+
 def test_local_engine_save_load(data: list[Collection], tmp_path):
     db = LocalEngine()