Request Body in FastAPI

Request data model

We usually need to send the data to an API for processing. This data is called request data. A request body is data sent by the client to your API. A response body is the data that your API sends to the client. The API almost always has to send a response body, but clients don’t necessarily need to send request bodies all the time.

To declare a request body in FastAPI, we can use Pydantic models with all their power and benefits. If you are not sure of these models, we will see them now.

To send request data, you should use one of the POST (commonly used), PUT, DELETE or PATCH methods. Sending a request body with a GET request has undefined behavior in the specifications. Nevertheless, it is supported by FastAPI only for very complex/extreme use cases. As it is not a common practice, the interactive docs with Swagger UI won’t show the documentation for the body when using GET.

Let us now see how this request body can be taken care of in FastAPI.