Bug: GenericSQLAlchemyConfig.get_engine doesn't save created engine to self.engine_instance if self.engine_instance not exists

[alex-loktev]

Description

Actually, I don't understand—is it a bug or a feature? I'm using this library for my app, and in my case, it's a bug.

I use OpenTelemetry's SQLAlchemyInstrumentor. To instrument SQLAlchemyInstrumentor, I need a SQLAlchemy engine. However, when I try to get the engine using GenericSQLAlchemyConfig.get_engine, it doesn't work correctly.

GenericSQLAlchemyConfig.get_engine is called twice: once during on_app_init and once when I try to get the engine. In this case, I need to provide my engine instance manually. Maybe we should store the created engine when using GenericSQLAlchemyConfig.get_engine?

URL to code causing the issue

No response

MCVE

def setup_plugins() -> list:
    plugins = []
    sqlalchemy_config = SQLAlchemyAsyncConfig(
        connection_string=str(ConfigInstance.env.db_url), # it's PostgresDSN
        engine_config=EngineConfig(
            poolclass=NullPool,
            connect_args={'statement_cache_size': 0},
        )
    )
    sqlalchemy_plugin = SQLAlchemyPlugin(
        config=sqlalchemy_config,
    )
    plugins.append(sqlalchemy_plugin)

    if ConfigInstance.env.app_environment == 'prod':
        SQLAlchemyInstrumentor().instrument(
            engine=sqlalchemy_config.get_engine().sync_engine
        )
        otel_plugin = OpenTelemetryPlugin(OpenTelemetryConfig())
        plugins.append(otel_plugin)
        
    return plugins

app = Litestar(
    route_handlers=controllers,
    plugins=setup_plugins(),
)

Steps to reproduce

Screenshots

No response

Logs

I added some logs to create_async_engine

INFO:     Started server process [22517]
INFO:     Waiting for application startup.
Created new engine instance (id=135510527018560)
Created new engine instance (id=135510525573632)
INFO:     Application startup complete.
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)

Package Version

advanced_alchemy==0.30.3
sqlalchemy==2.0.38

Platform

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