Delay global connection initialization

Author: rafalp

databases/core.py

@@ -72,12 +72,6 @@ def __init__(
         self._global_connection = None  # type: typing.Optional[Connection]
         self._global_transaction = None  # type: typing.Optional[Transaction]
 
-        if self._force_rollback:
-            self._global_connection = Connection(self._backend)
-            self._global_transaction = self._global_connection.transaction(
-                force_rollback=True
-            )
-
     async def connect(self) -> None:
         """
         Establish the connection pool.
@@ -91,7 +85,14 @@ async def connect(self) -> None:
         self.is_connected = True
 
         if self._force_rollback:
-            assert self._global_transaction is not None
+            assert self._global_connection is None
+            assert self._global_transaction is None
+
+            self._global_connection = Connection(self._backend)
+            self._global_transaction = self._global_connection.transaction(
+                force_rollback=True
+            )
+
             await self._global_transaction.__aenter__()
 
     async def disconnect(self) -> None:
@@ -101,9 +102,14 @@ async def disconnect(self) -> None:
         assert self.is_connected, "Already disconnected."
 
         if self._force_rollback:
+            assert self._global_connection is not None
             assert self._global_transaction is not None
+
             await self._global_transaction.__aexit__()
 
+            self._global_transaction = None
+            self._global_connection = None
+
         await self._backend.disconnect()
         logger.info(
             "Disconnected from database %s",