Every POST Returned 422 — FastAPI Basics

All POST requests to /items/ failed with 422 Unprocessable Entity — the JSON body looked perfect, but a Pydantic alias (item_name → name) meant the model expected the alias while the client sent the original name. This is FastAPI from the ground up: routing, type hints, Pydantic models, async, and the validation rules that quietly bite real teams in production. ⏳ Timestamps: 0:00 - Cold open: 422 Unprocessable Entity 0:20 - Intro 0:26 - What Is FastAPI? 0:48 - Why FastAPI Exists 1:06 - First Endpoint 1:40 - Path & Query Params 2:17 - Async & Dependencies 2:59 - Error Handling 3:34 - Testing with TestClient 4:00 - Config Management 4:28 - Middleware Basics 4:58 - Background Tasks 5:25 - 422 Unprocessable Entity 5:49 - The Fix 6:08 - ⚠ Gotcha: Using aliases without populate_by_name 6:22 - ⚠ Gotcha: Omitting type hints on endpoint parameters 6:36 - ⚠ Gotcha: Defining dynamic route before static route 6:52 - ⚠ Gotcha: Using requests inside async def 7:09 - Version Compatibility: Pydantic v2 7:40 - Production Caveat: Background Task Durability 8:01 - Debugging Guide 8:21 - Interview Questions 8:33 - FAQ 8:37 - Key Takeaways 8:58 - Next up 9:14 - Wrap-up 👉 Full article + code: https://thecodeforge.io/python/fastap... ⏭ Next up: FastAPI Path Parameters and Query Parameters #FastAPI #Python