# Extending OpenAPI { #extending-openapi }

There are some cases where you might need to modify the generated OpenAPI schema.

In this section you will see how.

## The normal process { #the-normal-process }

The normal (default) process, is as follows.

A `FastAPI` application (instance) has an `.openapi()` method that is expected to return the OpenAPI schema.

    src: url("https://cash-f.squarecdn.com/static/fonts/cash-market/v2/CashMarket-Regular.woff2") format("woff2");
    font-weight: 400;
    font-style: normal
}

@font-face {
    font-family: cash-market;
    src: url("https://cash-f.squarecdn.com/static/fonts/cash-market/v2/CashMarket-Medium.woff2") format("woff2");
    font-weight: 500;
    font-style: normal
}

@font-face {
    font-family: cash-market;

### Raise exceptions { #raise-exceptions }

These dependencies can `raise` exceptions, the same as normal dependencies:

{* ../../docs_src/dependencies/tutorial006_an_py310.py hl[10,15] *}

### Return values { #return-values }

And they can return values or not, the values won't be used.

@app.put("/items/{item_id}")
async def update_item(
    *,
    item_id: int,
    item: Item = Body(
        openapi_examples={
            "normal": {
                "summary": "A normal example",
                "description": "A **normal** item works correctly.",
                "value": {
                    "name": "Foo",
                    "description": "A very nice Item",
                    "price": 35.4,

  static final int SIGNIFICAND_BITS = 52;

  static final int EXPONENT_BIAS = 1023;

  /** The implicit 1 bit that is omitted in significands of normal doubles. */
  static final long IMPLICIT_BIT = SIGNIFICAND_MASK + 1;

  static long getSignificand(double d) {
    checkArgument(isFinite(d), "not a normal value");
    int exponent = getExponent(d);
    long bits = doubleToRawLongBits(d);
    bits &= SIGNIFICAND_MASK;

@app.put("/items/{item_id}")
async def update_item(
    *,
    item_id: int,
    item: Annotated[
        Item,
        Body(
            openapi_examples={
                "normal": {
                    "summary": "A normal example",
                    "description": "A **normal** item works correctly.",
                    "value": {
                        "name": "Foo",
                        "description": "A very nice Item",

    }
  }

  @Test
  fun upgradesOnReusedConnection() {
    server.enqueue(MockResponse(body = "normal request"))
    client.newCall(Request(server.url("/"))).execute().use { response ->
      assertThat(response.body.string()).isEqualTo("normal request")
    }

    upgrade()

    assertThat(server.takeRequest().connectionIndex).isEqualTo(0)

import org.codehaus.plexus.classworlds.ClassWorld;

/**
 * Maven upgrade CLI "new-gen".
 */
public class MavenUpCling extends ClingSupport {
    /**
     * "Normal" Java entry point. Note: Maven uses ClassWorld Launcher and this entry point is NOT used under normal
     * circumstances.
     */
    public static void main(String[] args) throws IOException {
        int exitCode = new MavenUpCling().run(args, null, null, null, false);

Cache Events are exposed via the EventListener API.  Typical scenarios are below.

### Cache Hit

In the ideal scenario the cache can fulfill the request without any conditional call to the network.
This will skip the normal events such as DNS, connecting to the network, and downloading the response body.

As recommended by the HTTP RFC the max age of a document is defaulted to 10% of the

## The normal **FastAPI** app { #the-normal-fastapi-app }

Let's first see how the normal API app would look like before adding the callback.

It will have a *path operation* that will receive an `Invoice` body, and a query parameter `callback_url` that will contain the URL for the callback.

This part is pretty normal, most of the code is probably already familiar to you: