Reset counter for failed connections (#385)

Co-authored-by: Sergey Morozov <sergey@morozov.top>

databases/core.py

@@ -237,8 +237,12 @@ def __init__(self, backend: DatabaseBackend) -> None:
     async def __aenter__(self) -> "Connection":
         async with self._connection_lock:
             self._connection_counter += 1
-            if self._connection_counter == 1:
-                await self._connection.acquire()
+            try:
+                if self._connection_counter == 1:
+                    await self._connection.acquire()
+            except Exception as e:
+                self._connection_counter -= 1
+                raise e
         return self
 
     async def __aexit__(

tests/test_databases.py

@@ -4,6 +4,7 @@
 import functools
 import os
 import re
+from unittest.mock import patch, MagicMock
 
 import pytest
 import sqlalchemy
@@ -15,6 +16,11 @@
 DATABASE_URLS = [url.strip() for url in os.environ["TEST_DATABASE_URLS"].split(",")]
 
 
+class AsyncMock(MagicMock):
+    async def __call__(self, *args, **kwargs):
+        return super(AsyncMock, self).__call__(*args, **kwargs)
+
+
 class MyEpochType(sqlalchemy.types.TypeDecorator):
     impl = sqlalchemy.Integer
 
@@ -267,6 +273,30 @@ async def test_ddl_queries(database_url):
             await database.execute(query)
 
 
+@pytest.mark.parametrize("database_url", DATABASE_URLS)
+@async_adapter
+async def test_queries_after_error(database_url):
+    """
+    Test that the basic `execute()` works after a previous error.
+    """
+
+    class DBException(Exception):
+        pass
+
+    async with Database(database_url) as database:
+        with patch.object(
+            database.connection()._connection,
+            "acquire",
+            new=AsyncMock(side_effect=DBException),
+        ):
+            with pytest.raises(DBException):
+                query = notes.select()
+                await database.fetch_all(query)
+
+        query = notes.select()
+        await database.fetch_all(query)
+
+
 @pytest.mark.parametrize("database_url", DATABASE_URLS)
 @async_adapter
 async def test_results_support_mapping_interface(database_url):