Fix a DetachedInstanceError that only shows up after the session closes

My API returns a 500 the moment it tries to read a relationship, but only sometimes, and the trace points at code that never touches the database.

IntermediateRead 6 minDoing: under an hour6 steps

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What you'll have at the end

An endpoint that loads every relationship before the session closes, with no more DetachedInstanceError crashes on repeated calls

Before you start

You need

A route that already queries an object through a session-per-request pattern and serializes it into a response model naming one of that object's relationships.

Not covered

Handing this same object to a background task or a second thread after the request ends; that needs its own fresh session opened after the request is gone.

Leans on

6 steps

Where to go next

Find and fix the N+1 queries hiding in a nested API response

when a relationship loads fine but fires one extra query per row instead of raising an error, that is the performance problem this sibling recipe fixes.

Checked 18 Aug 2026

Part of the ORM and Database Abstraction Tools cookbook