Handling GET Requests in FastAPI

Key Concepts

1. GET Requests

GET requests are used to retrieve data from a server. They are one of the most common HTTP methods and are typically used for reading or fetching resources. Unlike POST or PUT requests, GET requests do not modify data on the server.

2. Path Parameters

Path parameters are variables that are part of the URL path. They are used to identify a specific resource or a set of resources. In FastAPI, you can define path parameters in your route paths using curly braces {}.

3. Query Parameters

Query parameters are additional data sent with the URL after a question mark ?. They are used to filter or sort the data being requested. In FastAPI, query parameters are defined as optional arguments in your route handler functions.

Detailed Explanation

1. GET Requests

When a client makes a GET request to a server, the server responds with the requested resource. The data is typically returned in the form of JSON, HTML, or XML. GET requests are idempotent, meaning that making the same request multiple times will yield the same result without side effects.

2. Path Parameters

Path parameters are essential for creating dynamic routes. For example, if you want to retrieve a specific user by their ID, you can define a path parameter in your route. FastAPI automatically validates and converts the path parameter to the specified type.

3. Query Parameters

Query parameters provide a way to pass additional information to the server without modifying the path. They are useful for filtering, sorting, or paginating data. FastAPI allows you to define query parameters as optional arguments in your route handler functions, making it easy to handle various request scenarios.

Examples

Example 1: Basic GET Request

Here is a simple example of handling a GET request in FastAPI:

from fastapi import FastAPI

app = FastAPI()

@app.get("/")
async def read_root():
    return {"message": "Hello, World!"}
    

Example 2: GET Request with Path Parameter

In this example, we define a route that accepts a path parameter to retrieve a specific user:

from fastapi import FastAPI

app = FastAPI()

@app.get("/users/{user_id}")
async def read_user(user_id: int):
    return {"user_id": user_id, "username": "john_doe"}
    

Example 3: GET Request with Query Parameter

Here, we define a route that accepts a query parameter to filter users by their status:

from fastapi import FastAPI

app = FastAPI()

@app.get("/users/")
async def read_users(status: str = None):
    if status:
        return {"status": status, "users": ["user1", "user2"]}
    return {"users": ["user1", "user2", "user3"]}
    

Analogies

Think of a GET request as ordering a book from a library. The library (server) retrieves the book (resource) and sends it to you (client). The path parameter is like specifying the exact book title, while the query parameter is like asking for books by a specific author or genre.

Another analogy is a restaurant menu. A GET request is like reading the menu to see what dishes are available. The path parameter is like choosing a specific dish, and the query parameter is like asking for dishes that are spicy or vegetarian.