python runtime_error ai_generated true

sqlalchemy.orm.exc.DetachedInstanceError: Instance <User at 0x...> is detached; merge() cannot proceed because the session already has a different instance with the same primary key

ID: python/sqlalchemy-orm-exc-detached-instance-merge-conflict

Also available as: JSON · Markdown · 中文
80%Fix Rate
82%Confidence
0Evidence
2025-09-14First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
3.x active — — —

Root Cause

Attempting to merge a detached instance when the session already tracks another instance with the same primary key, causing identity conflict.

generic

中文

尝试合并一个分离的实例，但会话已跟踪另一个具有相同主键的实例，导致身份冲突。

Workarounds

  1. 85% success Expunge existing instance first 
    Expunge the existing instance from session before merge: session.expunge(existing_instance); session.merge(detached_instance)
  2. 90% success Merge with clean session 
    Use session.merge() with a new instance that does not conflict, or ensure the session is clean before merging.

Dead Ends

Common approaches that don't work:

  1. Deleting existing instance 60% fail

  2. Using add() instead 70% fail