Dear all, I am quite new to ORMs and SQLAlchemy, and I have a maybe somewhat naive question set regarding how to build an application around a database.
Just a few words of context (may not yield importance, but who knows): I am building a mobile app, for which the server side will be an AWS Lambda function serving GraphQL queries. Data persistence is achieved through a hosted PostgreSQL instance. Server side code is python and "database access" through SQLAlchemy. The first version of the database schema has been "manually" built and populated with some test data (via simple SQL queries in pgAdmin4). Regarding SQLAlchemy usage, first version was using Core only, but I decided to move to ORM, and I got it quite hard - maybe because of poor choices on my end. What I do, now that I have a working example: - when the Lambda is fired, I import a module defining "bare" ORM classes, with no attribute apart the table name - inheriting from *`Reflected`* and a declarative base (using deferred reflection <https://docs.sqlalchemy.org/en/20/orm/declarative_tables.html#using-deferredreflection> ) - engine is set up and connection established to the db - *`Reflected`* class is prepared through *Reflected.prepare(engine=engine)* - New attributes, relationships, etc... are added to the "bare" ORM classes as *`column_property`*, after reflection (this way <https://docs.sqlalchemy.org/en/20/orm/mapped_sql_expr.html#adding-column-property-to-an-existing-declarative-mapped-class> ) - Mapper is then ready, data is queried and mutated using sessions My questions are: - is reflection mandatory when working with an existing database? (I think this would be like an overwhelmingly prevalent case for Production applications?) - is it possible to have a mixed approach regarding the mapping definitions: some attributes being defined in the ORM classes prior to the reflection, and reflection then completes those classes with other fields from the database schema? - when using reflection, is the only way to define new attributes, relationships, etc... to add those attributes after this reflection via adding column_properties after class definition, like described above? - I feel like I am losing much of the "Declarative Mapping" by working the way I do, what do you think about it? - overall, what could be simplified regarding the ways of working I set up? Some code snippets below: *Bare ORM class definitions:* class MessageOrm(Reflected, Base): __tablename__ = "single_recipient_message" class HeaderOrm(Reflected, Base): __tablename__ = "single_recipient_message_header" *Post reflection addition of relationships and attributes* HeaderOrm.messages = relationship( MessageOrm, foreign_keys=[MessageOrm.header_id], back_populates="header", ) MessageOrm.sent_by_who = column_property( case( (MessageOrm.sender_id == current_id, "me"), else_="other", ) ) MessageOrm.header = relationship( "HeaderOrm", foreign_keys=[MessageOrm.header_id], back_populates="messages", ) Thanks a lot! Regards, Pierre -- SQLAlchemy - The Python SQL Toolkit and Object Relational Mapper http://www.sqlalchemy.org/ To post example code, please provide an MCVE: Minimal, Complete, and Verifiable Example. See http://stackoverflow.com/help/mcve for a full description. --- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sqlalchemy/433f9917-7ac0-4d1b-b41e-16d8ae255d15n%40googlegroups.com.
