In some cases, you may want to override the logic used by the `Request` and `APIRoute` classes.

In particular, this may be a good alternative to logic in a middleware.

For example, if you want to read or manipulate the request body before it is processed by your application.

/// danger

This is an "advanced" feature.

If you are just starting with **FastAPI** you might want to skip this section.

///

In this type of scenario, you probably would want to have **a single (Uvicorn) process per container**, as you would already be handling replication at the cluster level.

So, in this case, you **would not** want to have a multiple workers in the container, for example with the `--workers` command line option. You would want to have just a **single Uvicorn process** per container (but probably multiple containers).

///

/// note

This is supported since FastAPI version `0.113.0`. 🤓

///

## Pydantic Models for Forms { #pydantic-models-for-forms }

You just need to declare a **Pydantic model** with the fields you want to receive as **form fields**, and then declare the parameter as `Form`:

{* ../../docs_src/request_form_models/tutorial001_an_py310.py hl[9:11,15] *}

* installation
* activation
* update
* deactivation
* un-installation

When a plugin is installed we may want to check the license and make users agree. We may also want to unpack the given plugin in a particular location.

				VersionID:   "",
				IsLatest:    true,
				NumVersions: 1,
			},
			want: 0,
			lc:   lc,
		},
	}
	for i, tc := range tests {
		t.Run(fmt.Sprintf("test-%d", i+1), func(t *testing.T) {
			if got := tc.lc.FilterRules(tc.opts); len(got) != tc.want {
				t.Fatalf("Expected %d rules to match but got %d", tc.want, len(got))
			}
			w := httptest.NewRecorder()
			tc.lc.SetPredictionHeaders(w, tc.opts)

                is not available, instead of erroring out, the dependency result will
                be `None`.

                This is useful when you want to have optional authentication.

                It is also useful when you want to have authentication that can be
                provided in one of multiple optional ways (for example, with OpenID
                Connect or in a cookie).
                """

				failOnErr(err)
				_, err = hash.Write(data)
				failOnErr(err)
				got[conf] = map[ErasureAlgo]uint64{algo: hash.Sum64()}
			}

			if a, b := want[conf], got[conf]; !reflect.DeepEqual(a, b) {
				fmt.Fprintf(os.Stderr, "%v: error on self-test [d:%d,p:%d]: want %#v, got %#v\n", algo, conf[0], conf[1], a, b)
				ok = false
				continue
			}
			// Delete first shard and reconstruct...
			first := encoded[0]

<img src="/img/tutorial/query-param-models/image01.png">
</div>

## Forbid Extra Query Parameters { #forbid-extra-query-parameters }

In some special use cases (probably not very common), you might want to **restrict** the query parameters that you want to receive.

You can use Pydantic's model configuration to `forbid` any `extra` fields:

{* ../../docs_src/query_param_models/tutorial002_an_py310.py hl[10] *}

## Do not Separate Schemas { #do-not-separate-schemas }

Now, there are some cases where you might want to have the **same schema for input and output**.

Probably the main use case for this is if you already have some autogenerated client code/SDKs and you don't want to update all the autogenerated client code/SDKs yet, you probably will want to do it at some point, but maybe not right now.

			t.Errorf("Test %d: filtered headers do not match expected headers - got: %v , want: %v", i, test.Header, test.ExpectedHeader)
		}
		RemoveSensitiveEntries(metadata)
		if !areKeysEqual(test.ExpectedHeader, metadata) {
			t.Errorf("Test %d: filtered headers do not match expected headers - got: %v , want: %v", i, test.Header, test.ExpectedHeader)
		}
	}