Let's start with an example and then see it in detail.

We create an async function `lifespan()` with `yield` like this:

{* ../../docs_src/events/tutorial003.py hl[16,19] *}

    //                                                                           =========
    // keeping parsed request parameters, normal texts or uploaded files
    // keys are requested parameter names (treated as field name here)
    protected Map<String, Object> elementsAll; // lazy-loaded, then after not null
    protected Map<String, MultipartFormFile> elementsFile; // me too
    protected Map<String, String[]> elementsText; // me too

 */
@GwtCompatible
@SuppressWarnings("serial") // uses writeReplace(), not default serialization
final class SingletonImmutableSet<E> extends ImmutableSet<E> {
  // We deliberately avoid caching the asList and hashCode here, to ensure that with
  // compressed oops, a SingletonImmutableSet packs all the way down to the optimal 16 bytes.

  final transient E element;

  SingletonImmutableSet(E element) {

                verifyPropertyValue(propertyKey, filteredValue); // null checked
                return filterPropertyAsDefault(filteredValue); // not null here
            }

            private String getFromCache(final String propertyKey) {
                try {
                    return cache.get(propertyKey,

// Macro to verify that the field `struct_size` of STRUCT_OBJ is initialized.
// `struct_size` is used for struct member compatibility check between core TF
// and plug-ins with the same C API minor version. More info here:
// https://github.com/tensorflow/community/blob/master/rfcs/20200612-stream-executor-c-api/C_API_versioning_strategy.md
#define TF_VALIDATE_STRUCT_SIZE(STRUCT_NAME, STRUCT_OBJ, SIZE_VALUE_NAME) \

  // TODO(user): Consider separating Strings that we've defined here to capture
  // identifiable substrings of expected error messages, from Strings that we've defined
  // here to provide error messages.
  // TODO(user): Some Strings used in the subclasses can be added as static Strings
  // here too.
  static final String ERROR_PARALLEL_EDGE = "connected by a different edge";

	switch *flags.Spectre {
	default:
		log.Printf("unknown setting -spectre=%s", *flags.Spectre)
		os.Exit(2)
	case "":
		// nothing
	case "index":
		// known to compiler; ignore here so people can use
		// the same list with -gcflags=-spectre=LIST and -asmflags=-spectrre=LIST
	case "all", "ret":
		ctxt.Retpoline = true
	}

	ctxt.Bso = bufio.NewWriter(os.Stdout)
	defer ctxt.Bso.Flush()

        Activation activation = profile.getActivation();

        String jdk = activation.getJdk();

        // null case is covered by canDetermineActivation(), so we can do a straight startsWith() here.
        if (jdk.startsWith("[") || jdk.startsWith("(")) {
            try {
                return matchJdkVersionRange(jdk);
            } catch (InvalidVersionSpecificationException e) {

# SQL (Relational) Databases { #sql-relational-databases }

**FastAPI** doesn't require you to use a SQL (relational) database. But you can use **any database** that you want.

Here we'll see an example using <a href="https://sqlmodel.tiangolo.com/" class="external-link" target="_blank">SQLModel</a>.

  /*
   * If you do this test from common.eventbus.EventBusTest, it doesn't actually test the behavior.
   * That is, even if exactly the same method works from inside the common.eventbus package tests,
   * it can fail here.
   */
  public void testAnonymous() {
    AtomicReference<String> holder = new AtomicReference<>();
    AtomicInteger deliveries = new AtomicInteger();
    EventBus bus = new EventBus();
    bus.register(