# FastAPI

This section describes integration with FastAPI ASGI framework.

Note

FastAPI also provides OpenAPI support. The main difference is that, unlike FastAPI’s code-first approach, OpenAPI-core allows you to laverage your existing specification that alligns with API-First approach. You can read more about API-first vs. code-first in the Guide to API-first.

## Middleware

FastAPI can be integrated by middleware to apply OpenAPI validation to your entire application.

Add `FastAPIOpenAPIMiddleware` with OpenAPI object to your `middleware` list.

      from fastapi import FastAPI
      from openapi_core.contrib.fastapi.middlewares import FastAPIOpenAPIMiddleware

      app = FastAPI()
      app.add_middleware(FastAPIOpenAPIMiddleware, openapi=openapi)

After that all your requests and responses will be validated.

Also you have access to unmarshal result object with all unmarshalled request data through `openapi` scope of request object.

    async def homepage(request):
       # get parameters object with path, query, cookies and headers parameters
       unmarshalled_params = request.scope["openapi"].parameters
       # or specific location parameters
       unmarshalled_path_params = request.scope["openapi"].parameters.path

       # get body
       unmarshalled_body = request.scope["openapi"].body

       # get security data
       unmarshalled_security = request.scope["openapi"].security

### Response validation

You can skip response validation process: by setting `response_cls` to `None`

      app = FastAPI()
      app.add_middleware(
          FastAPIOpenAPIMiddleware,
          openapi=openapi,
          response_cls=None,
      )

## Low level

For low level integration see Starlette integration.