Fix SA list function using same connection (#794)

Author: Dreamsorcerer

aiohttp_admin/backends/sqlalchemy.py

@@ -275,20 +275,25 @@ async def get_list(self, params: GetListParams) -> tuple[list[Record], int]:
         offset = (params["pagination"]["page"] - 1) * per_page
 
         filters = params["filter"]
-        async with self._db.connect() as conn:
-            query = sa.select(self._table)
-            if filters:
-                query = query.where(*create_filters(self._table.c, filters))
-
-            count_t = conn.scalar(sa.select(sa.func.count()).select_from(query.subquery()))
-
-            sort_dir = sa.asc if params["sort"]["order"] == "ASC" else sa.desc
-            order_by: sa.UnaryExpression[object] = sort_dir(params["sort"]["field"])
-            stmt = query.offset(offset).limit(per_page).order_by(order_by)
-            result, count = await asyncio.gather(conn.execute(stmt), count_t)
-            entities = [r._asdict() for r in result]
-
-        return entities, count
+        query = sa.select(self._table)
+        if filters:
+            query = query.where(*create_filters(self._table.c, filters))
+
+        async def get_count() -> int:
+            async with self._db.connect() as conn:
+                count = await conn.scalar(sa.select(sa.func.count()).select_from(query.subquery()))
+                if count is None:
+                    raise RuntimeError("Failed to get count.")
+                return count
+
+        async def get_entities() -> list[Record]:
+            async with self._db.connect() as conn:
+                sort_dir = sa.asc if params["sort"]["order"] == "ASC" else sa.desc
+                order_by: sa.UnaryExpression[object] = sort_dir(params["sort"]["field"])
+                stmt = query.offset(offset).limit(per_page).order_by(order_by)
+                return [r._asdict() for r in await conn.execute(stmt)]
+
+        return await asyncio.gather(get_entities(), get_count())
 
     @handle_errors
     async def get_one(self, record_id: Any, meta: Meta) -> Record: