# Body - Nested Models { #body-nested-models }

With **FastAPI**, you can define, validate, document, and use arbitrarily deeply nested models (thanks to Pydantic).

## List fields { #list-fields }

You can define an attribute to be a subtype. For example, a Python `list`:

{* ../../docs_src/body_nested_models/tutorial001_py310.py hl[12] *}

This will make `tags` be a list, although it doesn't declare the type of the elements of the list.

    }

    @Test
    @DisplayName("Methods should handle null buffer without validation")
    void testMethodsWithNullBuffer() {
        // The implementation doesn't validate null buffers
        // These methods simply return 0 without accessing the buffer

        // Write methods return 0 without accessing null buffer
        assertEquals(0, response.writeSetupWireFormat(null, 0));

	var exp expirationWrapper
	err := d.DecodeElement(&exp, &startElement)
	if err != nil {
		return err
	}
	*e = Expiration(exp)
	e.set = true
	return nil
}

// Validate - validates the "Expiration" element
func (e Expiration) Validate() error {
	if !e.set {
		return nil
	}

	// DeleteMarker cannot be specified if date or dates are specified.
	if (!e.IsDaysNull() || !e.IsDateNull()) && e.DeleteMarker.set {

		fmt.Fprintln(os.Stderr, "reading input:", err)
	}
	fmt.Printf("%d\n", count)
	// Output: 15
}

// Use a Scanner with a custom split function (built by wrapping ScanWords) to validate
// 32-bit decimal input.
func ExampleScanner_custom() {
	// An artificial input source.
	const input = "1234 5678 1234567901234567890"
	scanner := bufio.NewScanner(strings.NewReader(input))

        return normalizedPath.startsWith(normalizedBase);
    }

    /**
     * Validates that a given file is safe and does not attempt path traversal attacks.
     * <p>
     * This is a convenience method that converts File objects to Path and calls
     * {@link #isPathSafe(Path, Path)}.
     * </p>
     *
     * @param fileToCheck the file to validate (must not be {@literal null})

 */

package org.elasticsearch.gradle.internal.precommit;

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.dataformat.yaml.YAMLFactory;

/**
 * Incremental task to validate a set of YAML files against against a schema.
 */
public class ValidateYamlAgainstSchemaTask extends ValidateJsonAgainstSchemaTask {
    @Override
    protected String getFileType() {
        return "YAML";
    }

/**
 * Validation annotation for URI type constraints.
 * This annotation validates URI strings based on specified protocol types.
 */
@Target({ METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER })
@Retention(RUNTIME)
@Documented
@Constraint(validatedBy = UriTypeValidator.class)
public @interface UriType {

    /**
     * Specifies the protocol type to validate against.
     *
     * @return the protocol type
     */

import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.Locale;
import java.util.Map;
import java.util.Set;
import java.util.stream.StreamSupport;

/**
 * Incremental task to validate that the API names in set of JSON files do not contain
 * programming language keywords.
 * <p>
 * The keywords are defined in a JSON file, although it's worth noting that what is and isn't a

     *
     * @param form the login form containing username and password
     * @return the HTML response after login attempt
     */
    @Execute
    public HtmlResponse login(final LoginForm form) {
        validate(form, messages -> {}, () -> asIndexPage(form));
        verifyToken(() -> asIndexPage(form));
        final String username = form.username;
        final String password = form.password;
        form.clearSecurityInfo();

import okhttp3.Response
import okhttp3.internal.http.RealInterceptorChain

/**
 * Opens a connection to the target server and proceeds to the next interceptor. The network might
 * be used for the returned response, or to validate a cached response with a conditional GET.
 */
object ConnectInterceptor : Interceptor {
  @Throws(IOException::class)
  override fun intercept(chain: Interceptor.Chain): Response {