Robust / configurable datetime handling in the admin API

[vsdudakov]

Summary

Datetime serialization/parsing through the admin is a recurring pain point. This is the strongest signal from the fork ecosystem: three independent forks all patched datetime handling.

Evidence from forks

• BoBaHPyt/fastadmin — a long chain of commits titled "fix datetime read error" (compare)
• ibeswipin/fastadmin — inherits the same "fix datetime read error" chain (compare)
• alex-averin/fastadmin — "Change response model for fastapi endpoints to correct datetime format" (compare)

When three unrelated users independently patch the same thing, it points to a real defect/UX gap.

Proposal

Audit datetime round-tripping in the API layer (read + write) and ensure values serialize/parse in a predictable, ISO-compliant format. Consider making the output format configurable (see the related custom-encoders request).

Filed from an analysis of all forks of this repo.

[vsdudakov]

Closing — after auditing the current codebase, the concrete "datetime read error" that the forks (BoBaHPyt/ibeswipin/alex-averin) patched is already resolved, and the remaining "configurable format" ask is delivered by #138.

Round-tripping is already ISO 8601 across all three frameworks:

• Flask — JSONProvider.default → date | time → .isoformat() (fastadmin/api/frameworks/flask/app.py:18)
• Django — JsonEncoder.default → datetime | time → .isoformat() (fastadmin/api/frameworks/django/app/api.py:36)
• FastAPI — default jsonable_encoder renders datetime/date/time as ISO 8601

Read side — BaseModelAdmin.deserialize_value parses the date/time pickers via datetime.fromisoformat (fastadmin/models/base.py:492).

Configurable output (the one open enhancement here) is now covered by #138, which adds register_encoder:

import datetime
from fastadmin import register_encoder

register_encoder(datetime.datetime, lambda dt: dt.strftime("%Y-%m-%d %H:%M"))

If a specific datetime read/write case still misbehaves, please reopen with a repro and ORM/framework details.