Cascade delete error: FOREIGN KEY constraint failed, with complex entity relationships

[andreymal]

from pony.orm import * 

db = Database()


class Author(db.Entity):
    post = Optional('Post', cascade_delete=True)
    edits = Set('PostEdit')

class Post(db.Entity):
    author = Required(Author)
    edits = Set('PostEdit')

class PostEdit(db.Entity):
    editor = Required(Author)
    post = Optional(Post)


db.bind('sqlite', ':memory:')
db.generate_mapping(create_tables=True)

# fill database
with db_session:
    Author(id=1)
    Post(author=1, id=1)
    PostEdit(id=1, editor=1, post=1)

# and crash it
with db_session:
    Author.get(id=1).delete()

Traceback (most recent call last):
  File "pony_cascade_test.py", line 33, in <module>
    Author.get(id=1).delete()
  File "/home/andreymal/.local/lib/python3.6/site-packages/pony/orm/core.py", line 394, in __exit__
    commit()
  File "/home/andreymal/.local/lib/python3.6/site-packages/pony/orm/dbapiprovider.py", line 52, in wrap_dbapi_exceptions
    except dbapi_module.IntegrityError as e: raise IntegrityError(e)
pony.orm.dbapiprovider.IntegrityError: FOREIGN KEY constraint failed

[sashaaero]

Hello! Yes, this is the bug that we will fix soon.
For now to get this code works you can do this:

# and crash it
with db_session:
    a = Author.get(id=1)
    a.edits.clear() # <- Add this line. This is the problem actually
    a.delete()

[sashaaero]

Done.