FastAPI – POST Endpoint and JSON Input

This section demonstrates how to handle POST requests in FastAPI to create new resources using request data and return JSON responses.

Example Application (POST Request)

Extend main.py with the following code:

from fastapi import FastAPI

app = FastAPI()

users = [
    {"name": "abbas", "age": 20},
    {"name": "mmd", "age": 37},
    {"name": "asghar", "age": 19},
]


@app.get("/")
def home_page():
    return {"msg": "API is working"}


@app.post("/new_user")
def create_user(name: str, age: int):
    new_user = {"name": name, "age": age}
    users.append(new_user)
    return {"msg": "User created successfully"}

Code Overview

POST Endpoint Definition

@app.post("/new_user")
def create_user(name: str, age: int):

Registers an HTTP POST endpoint at /new_user
Accepts input parameters:
- name → string
- age → integer
FastAPI automatically validates input types

Creating a New Resource

new_user = {"name": name, "age": age}
users.append(new_user)

Constructs a new user object
Appends it to the in-memory users list
Simulates creating a record in a database

JSON Response

return {"msg": "User created successfully"}

Returns a structured JSON response
Automatically serialized by FastAPI

Example Request

Using `curl`

curl -X POST "http://localhost:8000/new_user?name=ali&age=25"

Response

{
  "msg": "User created successfully"
}

Verifying the Result

After creating a user, retrieve the updated list:

GET /users

Response will now include the newly added user.

Running the Application

Start the FastAPI service using uvicorn:

uvicorn main:app --reload

Best Practices

POST requests should be used to create resources
Avoid modifying in-memory data in production environments
Use request bodies with Pydantic models instead of query parameters for real APIs
Return appropriate HTTP status codes (201 Created)
Validate and sanitize all client-provided input
Replace in-memory storage with persistent databases

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