src/flask/mongo/repository.py

@@ -46,6 +46,33 @@ class BeerRepository:
         self.run_meta = self.db["beer_runs"]
         self._ensure_indexes()
 
+    def close(self) -> None:
+        """Close the underlying Mongo client and release it.
+
+        A ``MongoClient`` keeps a connection pool and spawns three
+        monitoring threads.  ``close()`` alone does NOT reap them - they
+        go when the client object is garbage collected - so the
+        reference is dropped as well.
+
+        The request-scoped repository is closed by the app's teardown, but
+        a caller that builds its own - the advice background thread, for
+        instance - has to close it itself or the threads and the pool
+        accumulate, three per reading.
+        """
+        client = self.client
+        try:
+            client.close()
+        except Exception:
+            pass
+        # Drop the reference so the monitor threads can be reaped.
+        self.client = None
+
+    def __enter__(self) -> "BeerRepository":
+        return self
+
+    def __exit__(self, *exc_info) -> None:
+        self.close()
+
     def _ensure_indexes(self) -> None:
         """Make sure the lookup keys are indexed.
 
@@ -205,8 +232,10 @@ class BeerRepository:
         doc_id = _as_doc_id(reading_id)
         if doc_id is None:
             return 0
+        # `$in` matches either form.  A plain list would be an exact
+        # ARRAY match in Mongo, which is not what is wanted here.
         result = self.readings.update_one(
-            {"_id": doc_id},
+            {"_id": {"$in": doc_id}},
             {"$set": {
                 "advice": str(advice),
                 "advice_ok": bool(ok),
@@ -341,12 +370,42 @@ def _as_id(value: object) -> str:
     return ""
 
 
+#: A process-wide repository, for the code that runs outside a request.
+#:
+#: A ``MongoClient`` spawns three monitor threads and pymongo does not
+#: reap them on ``close()`` - they go only when the client is garbage
+#: collected.  So building a client per advice write accumulated three
+#: threads and a connection pool for every reading recorded.  One shared
+#: client for the life of the process is what the request-scoped
+#: repository does too.
+_shared_repository: "BeerRepository | None" = None
+
+
+def get_shared_repository() -> "BeerRepository":
+    """The process-wide repository, built on first use."""
+    global _shared_repository
+
+    if _shared_repository is None:
+        _shared_repository = BeerRepository()
+    return _shared_repository
+
+
 def _as_doc_id(value: object):
     """Coerce a reading document id to something Mongo will match.
 
-    The ``_id`` of a reading is an ``ObjectId``, not a run id, so the
-    ``_as_id`` coercion does not apply - it would turn the ObjectId into
-    an empty string and the update would silently match nothing.
+    The ``_id`` of a reading is not a run id, so the ``_as_id`` coercion
+    does not apply - it would turn the id into an empty string and the
+    update would silently match nothing.
+
+    Two shapes exist in this database:
+
+    - the ORIGINAL app's ids are 24 random CHARACTERS stored as a string
+      (``l78ZidBJ3QaYn98tvB88x4uM``), and
+    - ids written by Mongo itself are ``ObjectId`` objects.
+
+    So the id is returned in BOTH forms and the query matches either.
+    Accepting only the ObjectId form would mean the advice was never
+    stored for any of the existing readings.
 
     Only an ObjectId or a plain string is accepted, so a dict can never
     be injected as a query operator.
@@ -354,12 +413,15 @@ def _as_doc_id(value: object):
     from bson import ObjectId
 
     if isinstance(value, ObjectId):
-        return value
-    if isinstance(value, str):
+        return [value]
+    if isinstance(value, str) and value:
         try:
-            return ObjectId(value)
+            # A 24-character hex string may or may not be the stored
+            # ObjectId or the stored string, so try both.
+            return [ObjectId(value), value]
         except Exception:
-            return None
+            # Not hex - it can only be the original app's string id.
+            return [value]
     return None
 
 

src/flask/views/brews.py

@@ -89,7 +89,7 @@ def _start_advice(run_id: str, reading_id: str) -> None:
         for reading in run.readings:
             points = reading.sg_points
             readings.append({
-                "_id": reading._id,
+                "_id": str(reading._id),
                 "date": reading.date.isoformat() if reading.date else "",
                 "sg": points,
                 "sg_decimal": reading.sg_decimal,
@@ -98,7 +98,14 @@ def _start_advice(run_id: str, reading_id: str) -> None:
                 "final": bool(reading.final_reading),
             })
 
-        latest = dict(readings[-1]) if readings else {"date": "", "sg": None}
+        # The reading that is actually being advised about.  It is not
+        # necessarily the newest one: the brewer may be editing an older
+        # reading, and advice about the newest reading would be about the
+        # wrong number.
+        saved = next((r for r in readings if r.get("_id") == str(reading_id)), None)
+        if saved is None:
+            saved = dict(readings[-1]) if readings else {"date": "", "sg": None}
+        latest = dict(saved)
         latest["_id"] = reading_id
 
     except Exception:  # noqa: BLE001 - advice must never break the save
@@ -106,8 +113,21 @@ def _start_advice(run_id: str, reading_id: str) -> None:
         return
 
     def write(read_id: str, ok: bool, text: str) -> None:
-        from mongo.repository import BeerRepository
-        BeerRepository().set_reading_advice(read_id, text, ok)
+        # The client is SHARED, not built per reading.  A MongoClient
+        # spawns three monitor threads and pymongo does not reap them on
+        # close(), so building one per advice write accumulated three
+        # threads and a connection pool for every reading recorded.
+        #
+        # The shared client is created on first use and lives for the
+        # life of the process, which is what the request-scoped
+        # repository does too.
+        from mongo.repository import BeerRepository, get_shared_repository
+
+        try:
+            shared = get_shared_repository()
+            shared.set_reading_advice(read_id, text, ok)
+        except Exception:  # noqa: BLE001 - never let the thread die noisily
+            log.exception("could not store the generated advice")
 
     thread = threading.Thread(
         target=brew_advice.generate_advice_in_background,

tests/test_brew_advice.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import json
+from contextlib import contextmanager
 from datetime import date
 
 import pytest
@@ -248,6 +249,153 @@ def test_editing_a_reading_clears_its_stale_advice(repo):
     assert after["sg"] == "1030"
 
 
+def test_the_advice_is_stored_on_a_reading_with_a_string_id(repo):
+    """The original app's readings have 24-character STRING ids.
+
+    This is the shape every existing reading in the live database has -
+    the ids were generated by the old app as random characters, not by
+    Mongo.  A helper that only accepted an ObjectId would have matched
+    nothing, and the advice would silently never be stored.
+
+    The mongomock fixture generates ObjectIds, so this has to be
+    constructed explicitly or the bug is invisible in the tests.
+    """
+    repo.readings.insert_one({
+        "_id": "l78ZidBJ3QaYn98tvB88x4uM",
+        "beer_run_id": "1",
+        "beer_type": "Ale",
+        "sg": "1042",
+        "date": "2026-01-01",
+        "final_reading": "False",
+        "comment": "First ever try",
+    })
+
+    modified = repo.set_reading_advice("l78ZidBJ3QaYn98tvB88x4uM",
+                                        "THE ADVICE", True)
+    assert modified == 1, "the advice was not stored on a string-id reading"
+
+    after = repo.readings.find_one({"_id": "l78ZidBJ3QaYn98tvB88x4uM"})
+    assert after["advice"] == "THE ADVICE"
+    assert after["comment"] == "First ever try"
+
+
+def test_the_advice_is_stored_on_a_reading_with_an_object_id(repo):
+    """The other shape: a reading written by Mongo itself."""
+    seed_readings(repo, [("1", "Ale", "1042", "2026-01-01", False, "a comment")])
+    doc = repo.readings.find_one({"beer_run_id": "1"})
+
+    modified = repo.set_reading_advice(str(doc["_id"]), "THE ADVICE", True)
+    assert modified == 1
+
+    after = repo.readings.find_one({"beer_run_id": "1"})
+    assert after["advice"] == "THE ADVICE"
+
+
+def test_writing_the_advice_does_not_leak_a_client_per_reading():
+    """A MongoClient spawns three monitor threads and pymongo does not
+    reap them on close() - they go only when the client is collected.
+
+    So building a client per advice write accumulated three threads and a
+    connection pool for every reading recorded.  The advice writer shares
+    one client for the life of the process instead.
+    """
+    import inspect
+
+    from views import brews as brews_module
+
+    # The writer must NOT build a repository of its own - it has to use
+    # the shared one.  A MongoClient spawns three monitor threads and
+    # pymongo does not reap them on close(), so a client per advice write
+    # accumulated three threads and a connection pool for every reading
+    # recorded.
+    source = inspect.getsource(brews_module._start_advice)
+
+    assert "BeerRepository()" not in source, (
+        "the advice writer builds its own repository - that leaks a Mongo "
+        "client (three monitor threads) per reading"
+    )
+    assert "get_shared_repository" in source, (
+        "the advice writer must use the shared repository"
+    )
+
+
+@contextmanager
+def _app_with_repo(repo):
+    """An application context whose repository is *repo*.
+
+    The view reads the repository from ``app.extensions``, so pointing
+    that at a fixture is enough to drive the view's code directly.
+    """
+    from app_factory import create_app
+
+    app = create_app({
+        "TESTING": True,
+        "WTF_CSRF_ENABLED": False,
+        "SECRET_KEY": "test-secret",
+        "MONGO_CLIENT": repo.client,
+    })
+    # The advice must be generated even though this is a test app.
+    app.config["TESTING"] = False
+
+    original = app.extensions["beer_repo"]
+    app.extensions["beer_repo"] = lambda: repo
+    with app.app_context():
+        try:
+            yield app
+        finally:
+            app.extensions["beer_repo"] = original
+
+
+def test_the_advice_is_about_the_reading_that_was_saved():
+    """Editing an OLDER reading must not generate advice about the newest.
+
+    The advice is written against a specific reading, so the reading being
+    saved has to be the one the advice is about.
+    """
+    import time
+
+    import mongomock
+    from mongo.repository import BeerRepository
+    from views import brews as brews_module
+    from views.brews import _start_advice
+
+    captured = {}
+
+    def fake_generate(run, reading, history, writer=None):
+        captured["reading"] = reading
+        captured["history"] = history
+        return True, "THE ADVICE"
+
+    original = brews_module.brew_advice.generate_advice_in_background
+    brews_module.brew_advice.generate_advice_in_background = fake_generate
+    try:
+        # Two readings; the OLDER one is the one being saved.
+        repo = BeerRepository(client=mongomock.MongoClient())
+        old_id = repo.upsert_reading(beer_run_id="1", beer_type="Ale", sg=1042,
+                                     reading_date="2026-01-01", final_reading=False,
+                                     comment="first")
+        repo.upsert_reading(beer_run_id="1", beer_type="Ale", sg=1030,
+                            reading_date="2026-01-10", final_reading=False,
+                            comment="second")
+
+        # The advice is only generated when it is enabled, and it is off
+        # in testing.
+        with _app_with_repo(repo):
+            _start_advice("1", old_id)
+            for _ in range(40):
+                time.sleep(0.05)
+                if captured:
+                    break
+    finally:
+        brews_module.brew_advice.generate_advice_in_background = original
+
+    assert captured, "the advice was never generated"
+    assert captured["reading"]["_id"] == old_id
+    assert captured["reading"]["sg"] == 1042, (
+        "the advice was generated about the wrong reading"
+    )
+
+
 def test_the_reading_id_cannot_be_used_to_inject_a_query(repo):
     """The reading id is coerced before it reaches Mongo.