This can be very useful for setting up **resources** that you need to use for the whole app, and that are **shared** among requests, and/or that you need to **clean up** afterwards. For example, a database connection pool, or loading a shared machine learning model.

## Use Case { #use-case }

Let's start with an example **use case** and then see how to solve it with this.

OAuth2 was designed so that the backend or API could be independent of the server that authenticates the user.

But in this case, the same **FastAPI** application will handle the API and the authentication.

So, let's review it from that simplified point of view:

* The user types the `username` and `password` in the frontend, and hits `Enter`.

/**
 * Generates a dummy interface proxy that simply returns a dummy value for each method.
 *
 * @author Ben Yu
 */
@GwtIncompatible
@J2ktIncompatible
@NullMarked
abstract class DummyProxy {

  /**
   * Returns a new proxy for {@code interfaceType}. Proxies of the same interface are equal to each
   * other if the {@link DummyProxy} instance that created the proxies are equal.
   */

But now that FastAPI 0.99.0 and above uses OpenAPI 3.1.0, that uses JSON Schema 2020-12, and Swagger UI 5.0.0 and above, everything is more consistent and the examples are included in JSON Schema.

### Required, can be `None` { #required-can-be-none }

You can declare that a parameter can accept `None`, but that it's still required. This would force clients to send a value, even if the value is `None`.

To do that, you can declare that `None` is a valid type but simply do not declare a default value:

{* ../../docs_src/query_params_str_validations/tutorial006c_an_py310.py hl[9] *}

       - The compressed index.xml file contains a timestamp property which
       changes with every test execution, such that running the test
       actually changes the test classpath itself. This means that it
       can"t benefit from incremental build acceleration, because on every
       execution it sees that the classpath has changed, and so to be
       safe, it needs to re-run.

    }

    /**
     * Tests that <code>a:1.0</code> wins in the scenario:
     * <pre>
     * a:1.0
     * a:2.0
     * </pre>
     */
    @Test
    void testEqual() {
        ResolutionNode a1n = createResolutionNode(a1);
        ResolutionNode a2n = createResolutionNode(a2);

        assertResolveConflict(a1n, a1n, a2n);
    }

    /**
     * Tests that <code>a:2.0</code> wins in the scenario:

    }

    /**
     * Tests that <code>a:1.0</code> wins in the scenario:
     * <pre>
     * a:1.0
     * a:2.0
     * </pre>
     */
    @Test
    void testEqual() {
        ResolutionNode a1n = createResolutionNode(a1);
        ResolutionNode a2n = createResolutionNode(a2);

        assertResolveConflict(a1n, a1n, a2n);
    }

    /**
     * Tests that <code>a:2.0</code> wins in the scenario:

    }

    /**
     * Tests that <code>a:1.0</code> wins in the scenario:
     * <pre>
     * a:1.0
     * a:2.0
     * </pre>
     */
    @Test
    void testEqual() {
        ResolutionNode a1n = createResolutionNode(a1);
        ResolutionNode a2n = createResolutionNode(a2);

        assertResolveConflict(a1n, a1n, a2n);
    }

    /**
     * Tests that <code>a:1.0</code> wins in the scenario:

price.  Our General Public Licenses are designed to make sure that you
have the freedom to distribute copies of free software (and charge for
them if you wish), that you receive source code or can get it if you
want it, that you can change the software or use pieces of it in new
free programs, and that you know you can do these things.

  Developers that use our General Public Licenses protect your rights