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Developer tools · #sqlalchemy
DetachedInstanceError means the object lost its Session and the attribute was never loaded. Use inspect() to confirm, then fix session scope or loading strategy.
Detect and resolve SQLAlchemy N+1 query issues caused by lazy loading using echo, event listeners, and targeted eager loading.
Learn how lazy, joined, subquery, and selectin loaders affect query count and performance, with a concrete example and practical verification steps.
Scope SQLAlchemy 2.0 Sessions with Session.begin() to get atomic commits, avoid stale data and DetachedInstanceError. Use declarative mapping with Mapped and mapped_column and 2.0 select() queries.
Diagnose SQLAlchemy N+1 query problems with echo logging, then fix them by choosing joinedload or selectinload based on relationship type — and verify the query count stays flat.
A step‑by‑step guide to wiring SQLAlchemy 2.0's async ORM with PostgreSQL via asyncpg, covering engine creation, model definition, session handling, common pitfalls, and verification.
Learn how to set up SQLAlchemy 2.0’s AsyncEngine and AsyncSession for non‑blocking database access in FastAPI, including a working example, verification steps, and key limitations.
A decision guide for selecting SQLAlchemy session management—plain Session, scoped_session, or AsyncSession—in multi-threaded web applications. Includes a comparison table, trade-offs, a Flask-style implementation, and a validation script to verify thread-local isolation and connection cleanup.
FastAPI's Depends system eliminates duplicated session and auth code across endpoints. A worked example shows yield-based cleanup, per-request caching, and how to verify both behaviors yourself.
python
fastapi