advanced
Identity map
Keep one in-memory object per database row inside a request context to preserve identity and change tracking.
An identity map ensures one database row maps to one object instance within a request context. It supports change tracking and consistent object graphs in Data Mapper style ORMs.
Request fork
load Order#1 → instance A
load Order#1 again → same instance A
On interviews: request scoping, entity identity, stale reads, serialization, and dangers of global entity managers.
Common pitfalls: sharing identity maps across requests leaking user state; detached entities behaving unlike plain DTOs.
The trade-off is object graph consistency versus scope discipline.
Checklist:
- Scope identity map per request.
- Know attached versus detached entities.
- Avoid global mutable persistence state.
- Clear context after request ends.