11. HTTP Methods in Practice: GET & POST

Practical Usage of GET and POST in FastAPI

GET and POST represent two fundamentally different interaction patterns in FastAPI. GET is used for safe, read-only operations where no server-side state is modified, while POST is intended for operations that create or process data. Correct usage ensures predictable behavior, proper caching, and alignment with HTTP standards across APIs and web applications.

from fastapi import FastAPI

app = FastAPI()

@app.get("/tourists")
def list_tourists():
    return {"message": "List of tourists"}

@app.post("/tourists")
def create_tourist(tourist: dict):
    return {"message": "Tourist created", "data": tourist}

---

Query Parameters vs Request Bodies

Query parameters are best suited for filtering, pagination, and optional modifiers of a request. Request bodies are used when structured or sensitive data must be submitted to the server. FastAPI enforces this distinction through typing and validation, preventing ambiguous or unsafe API designs.

from fastapi import FastAPI

app = FastAPI()

@app.get("/search")
def search_tourists(country: str | None = None, limit: int = 10):
    return {"country": country, "limit": limit}

@app.post("/register")
def register_tourist(payload: dict):
    return payload

---

Handling Forms, Filters, and Submissions Correctly

Web applications often rely on form submissions, which naturally map to POST requests. FastAPI provides explicit support for form data while maintaining strong validation. Filters and search criteria should remain in GET requests to preserve idempotency and readability.

from fastapi import FastAPI, Form

app = FastAPI()

@app.post("/login")
def login(username: str = Form(...), password: str = Form(...)):
    return {"user": username}