Hi all! I wrote backend rest - fastapi - pony app on python 3.8 and i got exceptions in this block of code - TypeError: Entity instance or a sequence of instances expected. Got: <pony.orm.core.QueryResultIterator object at 0x10560e150>

It seems that you are using serialization module. It was an experimental module which is currently not supported. Try to use Entity.to_dict() method for serialization instead

Actually, the query does not look particularly complex

with open('myfile') as f: data = f.read() obj.field = data

What is the point storing files in db?

- it may be easier to achieve consistency. If database field stores filename only, then the file can be removed from the filesystem and the database will not know about it. - it is easier to copy entire database to another machine this way - it requires less efforts comparing to maintaining correct directory structure But it has drawbacks as well, so this is a tradeoff

Hi, @metaprogrammer . i get this error DatabaseSessionIsOver when i try to access print(bool(user.cars)) but i don't get it when i try for example print(bool(user.language)). my model is like class User(db.Entrity): ... cars = Set("car") class Car(db.Entity): ... owner = Required(User)

It is expected if you are trying to access the content of user.cars outside of the original db_session. user.cars is a relationship and needs additional SQL query to be loaded, and queries are possible inside db_session only. It is better to move all code that works with ORM objects into the db_session (including these prints). If it is impossible for some reason, as a workaround you can access user.cars inside db_session. Then it will be loaded from the database and cached, and you will be able to access it later.

Is something like @db_session def get_relationship(u,r): return getattr(u, r) "Nice"? I mean, whether it's ok or not.

It doesn't look correct. - db_session purpose is to denote transaction boundaries. At the start of db_session Pony grabs the database connection from the connection pool, and at the end of db_session Pony commits the transaction and returns the connection to the pool. - It is possible to have nested db_session, but inner db_sessions are ignored (maybe in the future releases of Pony nested db_sessions will start nested transactions). - Your get_relationship function clearly does not represent an entire transaction, as it receives an u object from the outside. This means that you already have db_session in the outer scope where you retrieved the u object from the database, and the nested db_session around the get_relationship function will be ignored. > Why i could pass it to print() outside the db_session, and It didn’t raise the error? If some object attributes were retrieved during the db_session, their values are still available even after the db_session was finished. As they were already retrieved from the database, they don't need a new query. But it is better to work with all objects inside db_session.

It doesn't look correct. - db_session purpose is to denote transaction boundaries. At the start of db_session Pony grabs the database connection from the connection pool, and at the end of db_session Pony commits the transaction and returns the connection to the pool. - It is possible to have nested db_session, but inner db_sessions are ignored (maybe in the future releases of Pony nested db_sessions will start nested transactions). - Your get_relationship function clearly does not represent an entire transaction, as it receives an u object from the outside. This means that you already have db_session in the outer scope where you retrieved the u object from the database, and the nested db_session around the get_relationship function will be ignored. > Why i could pass it to print() outside the db_session, and It didn’t raise the error? If some object attributes were retrieved during the db_session, their values are still available even after the db_session was finished. As they were already retrieved from the database, they don't need a new query. But it is better to work with all objects inside db_session.

You speak about three different functions, get_user, get_relationship and get_or_insert and don't show how they are interacting

about 3: It isn’t inner, it’s like database/utilities.py# ... @db_session def get_or_insert(self, **properties): user = User.get(**properties) if not user: user = User(**properties) return user project/file.py from ..database.utilities import get_user user = get_or_insert(id=3) And then i can pass ‘user’ to get_relationship in order to get the relationship, and it will happen in its own @db_session, the function doesn’t get called from another db_session-wrapped function.

1. return just u 2. move db_session up in the stack, so all actions with u are wrapped into this db_session

Also you can apply db_session in the middleware of your web framework to avoid wrapping of each individual endpoint