sqlalchemy: get rows affected by bulk delete

Question

I need to get all rows that were affected by a bulk delete like that:

Session.query(SomeClass).filter_by(foo='bar').delete()

I found the possibility to subscribe to bulk delete events but can't figure out how I can use this event to actually get the information I need.

Answer 1

Okay, found the answer \\☺/ You can re-execute the select statement that was used to select the rows for bulk deletion. Unfortunately you can't query the ORM objects, but you can get a list of all the deleted rows with the old column values as tuples:

def after_bulk_delete(session, query, query_context, result):
    affected_table = query_context.statement.froms[0]
    affected_rows = query_context.statement.execute().fetchall() 

sqlalchemy.event.listen(Session, "after_bulk_delete", after_bulk_delete)

Answer 2

From

https://docs.sqlalchemy.org/en/latest/orm/query.html#sqlalchemy.orm.query.Query.delete

Perform a bulk delete query.

Deletes rows matched by this query from the database.

Returns: the count of rows matched as returned by the database's “row count” feature.