# Body - Fields { #body-fields }

The same way you can declare additional validation and metadata in *path operation function* parameters with `Query`, `Path` and `Body`, you can declare validation and metadata inside of Pydantic models using Pydantic's `Field`.

## Import `Field` { #import-field }

First, you have to import it:

{* ../../docs_src/body_fields/tutorial001_an_py310.py hl[4] *}


/// warning

import org.junit.runners.Parameterized;
import org.junit.runners.Parameterized.Parameters;

/** Tests for a directed {@link ImmutableNetwork}. */
@AndroidIncompatible
@RunWith(Parameterized.class)
@NullUnmarked
public class StandardImmutableDirectedNetworkTest extends AbstractStandardDirectedNetworkTest {

  @Parameters(name = "allowsSelfLoops={0}, allowsParallelEdges={1}, nodeOrder={2}, edgeOrder={3}")

# Optional Path parameters are not supported...

paths:
  /documents:
    get:
      tags:
        - search
      summary: Finds documents by query
      description: Finds documents by search conditions
      operationId: searchDocuments
      parameters:
        - name: q
          in: query
          description: Search words
          required: false
          schema:
            type: string
            example: Fess
        - name: start

 *
 * @since 4.0.0
 */
@Experimental
public interface ArtifactFactory extends Service {

    /**
     * Creates an artifact.
     *
     * @param request the request holding artifact creation parameters
     * @return an {@code Artifact}, never {@code null}
     * @throws IllegalArgumentException if {@code request} is null or {@code request.session} is null or invalid
     */
    @Nonnull

   * {@code lexicographical(Collections.reverseOrder(comparator))} (consider how each would order
   * {@code [1]} and {@code [1, 1]}).
   */
  // Note: 90% of the time we don't add type parameters or wildcards that serve only to "tweak" the
  // desired return type. However, *nested* generics introduce a special class of problems that we
  // think tip it over into being worthwhile.

import jakarta.validation.constraints.Size;

/**
 * Form class for cache-related operations.
 * Contains parameters for document caching and error page display.
 */
public class CacheForm {

    /** Document ID for cache operations. */
    @Required
    @Size(max = 100)
    public String docId;

    /** Highlight query parameters. */
    public String[] hq;

    /** Search query parameter for error page. */
    public String q;

     */
    public interface XContentBuilderCallback {
        /**
         * Applies custom logic to build XContent using the provided builder and parameters.
         *
         * @param builder the XContentBuilder to use for building content
         * @param params the parameters to use during content building
         * @return the modified XContentBuilder
         * @throws IOException if an IO error occurs during building

// TODO Simplify the buildTimestamp() calculation if possible
fun Project.buildTimestamp(): Provider<String> =
    providers.of(BuildTimestampValueSource::class) {
        parameters {
            buildTimestampFromBuildReceipt = buildTimestampFromBuildReceipt()
            buildTimestampFromGradleProperty = buildTimestamp
            runningOnCi = buildRunningOnCi

    return {"p": p.p}


@pytest.mark.parametrize(
    "path",
    ["/optional-str", "/model-optional-str"],
)
def test_optional_str_schema(path: str):
    assert app.openapi()["paths"][path]["get"]["parameters"] == snapshot(
        [
            {
                "required": False,
                "schema": {
                    "anyOf": [{"type": "string"}, {"type": "null"}],
                    "title": "P",