refactor(packaging): Use SQLAlchemy event for Filename registry (Fixes #576)

warehouse/forklift/legacy.py

@@ -1530,11 +1530,6 @@ def file_upload(request):
                     f"Invalid attestations supplied during upload: {e}",
                 )
 
-        # TODO: This should be handled by some sort of database trigger or a
-        #       SQLAlchemy hook or the like instead of doing it inline in this
-        #       view.
-        request.db.add(Filename(filename=filename))
-
         # Store the information about the file in the database.
         file_ = File(
             release=release,

warehouse/packaging/models.py

@@ -25,6 +25,7 @@
     Text,
     UniqueConstraint,
     cast,
+    event,
     func,
     or_,
     orm,
@@ -1207,3 +1208,20 @@ class AlternateRepository(db.Model):
     name: Mapped[str]
     url: Mapped[str]
     description: Mapped[str]
+
+
+@event.listens_for(File, "after_insert")
+def add_filename_to_registry(mapper, connection, target):
+    """
+    Log the new filename to the Filename (file_registry) table.
+
+    This event listener is triggered *after* a new `File` object is
+    successfully inserted into the database.
+
+    We use a direct connection-level insert (`connection.execute()`)
+    instead of `session.add(Filename(...))` to avoid an `SAWarning`.
+    Modifying the session *during* the flush process (which is when
+    this hook runs) is not a supported operation. This method
+    bypasses the session's unit-of-work tracking and is safe here.
+    """
+    connection.execute(Filename.__table__.insert(), {"filename": target.filename})