How to create a POST Endpoint and define a Request Body in FastAPI

Introduction

FastAPI is a modern web framework that empowers developers to build web APIs quickly and efficiently using Python. A POST endpoint in FastAPI allows clients to submit data to the server, often for creating new resources. One part of a POST request ist the Request Body, which contains the data you want to send to the server. In this tutorial, we’ll explain how create a simple POST endpoint and how to define the request body in FastAPI.

Goal

Prerequisites

☑️ Set up a virtual environment in the root of your project directory

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☑️ Set up a FastAPI project

How to set up a FastAPI Project

Introduction FastAPI has quickly gained popularity as a modern, fast and easy-to-use Python web framework for building RESTful APIs. In this tutorial, we show you step-by-step how to set up a FastAPI project. Prerequisites First of all, make sure you have Python installed on your system. Furthermore, it is recommended

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What is a POST Endpoint?

A POST endpoint is a specific URL in an API where clients send data to the server to create a new resource.

What is a Request Body?

In a POST request the request body is the part of the request that contains the data you want to send to the server. For example, when you submit a form, that data is included in the request body. The server then processes this data to perform actions like creating a user, updating records, or uploading files.

Step 1: Import Libraries

First, we import the following python modules:

from fastapi import FastAPI, HTTPException
from pydantic import BaseModel

Step 2: Define Sample Data

Imagine a system where you can find information about various online courses. Let's define a sample database:

sample_courses_db = [
    {"course_id": "c1", "course_name": "Data Science"}, 
    {"course_id": "c2", "course_name": "Data Engineering"}, 
    {"course_id": "c3", "course_name": "Data Analytics"}
    ]

Step 3: Create FastAPI Instance

Let's create a FastAPI instance:

app = FastAPI()

Step 4: Define Request Body

Let's define a request body for the POST endpoint. The request body should contain the course_id and the  course_name. In order to define a request body we create the following Pydantic model:

class Course(BaseModel):
    course_id: str
    course_name: str | None = None

Step 5: Create POST Endpoint

Now, we want to create a POST endpoint that should meet the following requirements:

• If the course_id doesn't exist add it to the sample database.
• If the course_id already exists in the database an error message should be raised.

Let's set up a POST endpoint: