db: Raise an exception if the user_version is too new

Future proof. If we update the database schema, then we'll bump the
user_version field. If the user then tries to open the new database with
an old Emmental version then there could be a lot of issues. Let's
detect this and raise an error with a description of the problem.

Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

emmental/db/__init__.py

@@ -29,11 +29,7 @@ class Connection(connection.Connection):
     def __init__(self):
         """Initialize a sqlite connection."""
         super().__init__()
-
-        match self("PRAGMA user_version").fetchone()["user_version"]:
-            case 0:
-                with open(SQL_SCRIPT) as f:
-                    self._sql.executescript(f.read())
+        self.__check_version()
 
         self.settings = settings.Table(self)
         self.playlists = playlists.Table(self)
@@ -47,6 +43,16 @@ class Connection(connection.Connection):
 
         self.tracks = tracks.Table(self)
 
+    def __check_version(self) -> None:
+        user_version = self("PRAGMA user_version").fetchone()["user_version"]
+        match user_version:
+            case 0:
+                with open(SQL_SCRIPT) as f:
+                    self._sql.executescript(f.read())
+            case 1: pass
+            case _:
+                raise Exception(f"Unsupported data version: {user_version}")
+
     def close(self) -> None:
         """Close the database connection."""
         self.settings.stop()

tests/db/test_db.py

@@ -23,6 +23,15 @@ class TestConnection(tests.util.TestCase):
         cur = self.sql("PRAGMA user_version")
         self.assertEqual(cur.fetchone()["user_version"], 1)
 
+    def test_version_too_new(self):
+        """Test failing when the database version is too new."""
+        self.sql._Connection__check_version()
+
+        self.sql("PRAGMA user_version = 2")
+        with self.assertRaises(Exception) as e:
+            self.sql._Connection__check_version()
+        self.assertEqual(str(e.exception), "Unsupported data version: 2")
+
     def test_close(self):
         """Check closing the connection."""
         self.sql.settings.queue.running = True