# Using Dataclasses { #using-dataclasses }

FastAPI is built on top of **Pydantic**, and I have been showing you how to use Pydantic models to declare requests and responses.

But FastAPI also supports using <a href="https://docs.python.org/3/library/dataclasses.html" class="external-link" target="_blank">`dataclasses`</a> the same way:

{* ../../docs_src/dataclasses/tutorial001.py hl[1,7:12,19:20] *}

And then you also read how to handle [CORS with the `CORSMiddleware`](../tutorial/cors.md){.internal-link target=_blank}.

In this section we'll see how to use other middlewares.

## Adding ASGI middlewares { #adding-asgi-middlewares }

 *
 * <p>{@link #setDefault} allows subclasses to specify default values for types.
 *
 * <p>This class incurs IO because it scans the classpath and reads classpath resources.
 *
 * @author Ben Yu
 * @since 14.0
 */
// TODO: Switch to JUnit 4 and use @Parameterized and @BeforeClass
// Note: @Test annotations are deliberate, as some subclasses specify @RunWith(JUnit4).
@GwtIncompatible
@J2ktIncompatible

   * signed longs.
   */
  private static long flip(long a) {
    return a ^ Long.MIN_VALUE;
  }

  /**
   * Compares the two specified {@code long} values, treating them as unsigned values between {@code
   * 0} and {@code 2^64 - 1} inclusive.
   *
   * <p><b>Note:</b> this method is now unnecessary and should be treated as deprecated; use the

	if len(users2) != 1 {
		t.Errorf("should find one users using left join with conditions, but got %v", len(users2))
	}

	var users3 []User

 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.maven.api;

import org.apache.maven.api.annotations.Experimental;

/**
 * Represents a Java toolchain in the Maven build system.
 *
 * <p>A Java toolchain is a specific type of toolchain that provides access
 * to Java development tools, such as the Java compiler and Java runtime

    """STS aware XML parsing class. Wraps a root element name and
    cElementTree.Element instance. Provides STS namespace aware parsing
    functions.

    """

    def __init__(self, root_name, element):
        self.root_name = root_name
        self.element = element

    @classmethod
    def fromstring(cls, root_name, data):
        """Initialize STSElement from name and XML string data.

import org.codelibs.fess.mylasta.direction.FessConfig;
import org.codelibs.fess.util.ComponentUtil;

/**
 * Interface for transforming and processing crawled documents in Fess.
 * Provides utility methods for URL processing, site extraction, data mapping,
 * and field configuration handling during the document transformation process.
 */
public interface FessTransformer {

    /**

   * // returns {"foo", "quux"}
   * }
   *
   * <p>This {@code Collector} uses O(k) memory and takes expected time O(n) (worst-case O(n log
   * k)), as opposed to e.g. {@code Stream.sorted(comparator).limit(k)}, which currently takes O(n
   * log n) time and O(n) space.
   *
   * @throws IllegalArgumentException if {@code k < 0}
   * @since 22.0
   */

		pathToDelete       string
		objectsAfterDelete []string
	}{
		// Test 1: removes an object and checks it is the only object
		// that has been deleted.
		{
			"bucket1",
			[]objectUpload{{"object0", "content"}, {"object1", "content"}},
			"object0",
			[]string{"object1"},
		},
		// Test 2: remove an object inside a directory and checks it is deleted
		// with its parent since this former becomes empty
		{
			"bucket2",