FastAPI routing explained in detail: path parameters, query parameters, request body,

Have you ever been confused about parameter handling when writing an interface?

How to write path parameters?

What is the difference between query parameters and request body parameters?

How to automatically type check and generate documents?

This article will take you to fully master the three most commonly used parameter types in FastAPI, and with Pydantic validation, you can easily build high-quality APIs!

Path Parameters
Path parameters appear in the URL, such as /users/{user_id}.

When accessing /users/123, FastAPI will automatically convert 123 to int and pass it into user_id.

Features:

Parameters are written in the URL path
Automatic type conversion
Commonly used for resource location (such as user ID)
Query Parameters
Query parameters are passed through the key-value pairs after the URL ?, for example /search?q=fastapi&limit=10.


Visit /search?q=fastapi&limit=5 Return:

Features:

Flexible parameter passing method, you can set default values
Automatic type verification, automatic document support
Commonly used for paging, filtering, searching
Request body parameters
When you need to pass complex structures such as JSON objects, you need to use request body parameters and combine them with Pydantic to define models.

Step 1: Define data model



Step 2: Receive the request body

Send the request:

FastAPI will:

Automatically convert JSON to objects
Automatically validate fields
Automatically generate API documentation
Mixed use (path + query + request body)
Three parameters can be used in combination:

Parameter validation and documentation enhancement
FastAPI supports setting restrictions and document descriptions through Query and Path:


Supported validations include:

Is it required (...)
Value range (ge=1)
Character length (max_length)
Automatically displayed in Swagger file
Summary

FastAPI's parameter processing is not only powerful, but also intelligent, automatic, and document-friendly, greatly improving the development experience and efficiency!