Use a ContextVar to manage the sql connection instance as an instance…

src/diracx/db/sql/utils.py

@@ -6,9 +6,10 @@
 import logging
 import os
 from abc import ABCMeta
+from contextvars import ContextVar
 from datetime import datetime, timedelta, timezone
 from functools import partial
-from typing import TYPE_CHECKING, AsyncIterator, Self
+from typing import TYPE_CHECKING, AsyncIterator, Self, cast
 
 from pydantic import parse_obj_as
 from sqlalchemy import Column as RawColumn
@@ -73,7 +74,12 @@ class BaseSQLDB(metaclass=ABCMeta):
     metadata: MetaData
 
     def __init__(self, db_url: str) -> None:
-        self._conn = None
+        # We use a ContextVar to make sure that self._conn
+        # is specific to each context, and avoid parallel
+        # route executions to overlap
+        self._conn: ContextVar[AsyncConnection | None] = ContextVar(
+            "_conn", default=None
+        )
         self._db_url = db_url
         self._engine: AsyncEngine | None = None
 
@@ -121,16 +127,22 @@ def transaction(cls) -> Self:
     def engine(self) -> AsyncEngine:
         """The engine to use for database operations.
 
+        It is normally not necessary to use the engine directly,
+        unless you are doing something special, like writing a
+        test fixture that gives you a db.
+
+
         Requires that the engine_context has been entered.
+
         """
         assert self._engine is not None, "engine_context must be entered"
         return self._engine
 
     @contextlib.asynccontextmanager
     async def engine_context(self) -> AsyncIterator[None]:
         """Context manage to manage the engine lifecycle.
-
-        Tables are automatically created upon entering
+        This is called once at the application startup
+        (see ``lifetime_functions``)
         """
         assert self._engine is None, "engine_context cannot be nested"
 
@@ -144,19 +156,30 @@ async def engine_context(self) -> AsyncIterator[None]:
 
     @property
     def conn(self) -> AsyncConnection:
-        if self._conn is None:
+        if self._conn.get() is None:
             raise RuntimeError(f"{self.__class__} was used before entering")
-        return self._conn
+        return cast(AsyncConnection, self._conn.get())
 
     async def __aenter__(self):
-        self._conn = await self.engine.connect().__aenter__()
+        """
+        Create a connection.
+        This is called by the Dependency mechanism (see ``db_transaction``),
+        It will create a new connection/transaction for each route call.
+        """
+
+        self._conn.set(await self.engine.connect().__aenter__())
         return self
 
     async def __aexit__(self, exc_type, exc, tb):
+        """
+        This is called when exciting a route.
+        If there was no exception, the changes in the DB are committed.
+        Otherwise, they are rollbacked.
+        """
         if exc_type is None:
-            await self._conn.commit()
-        await self._conn.__aexit__(exc_type, exc, tb)
-        self._conn = None
+            await self._conn.get().commit()
+        await self._conn.get().__aexit__(exc_type, exc, tb)
+        self._conn.set(None)
 
 
 def apply_search_filters(table, stmt, search):