与在*路径操作函数*中使用 `Query`、`Path` 、`Body` 声明校验与元数据的方式一样，可以使用 Pydantic 的 `Field` 在 Pydantic 模型内部声明校验和元数据。

## 导入 `Field` { #import-field }

首先，从 Pydantic 中导入 `Field`：

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

/// warning | 警告

注意，与从 `fastapi` 导入 `Query`，`Path`、`Body` 不同，要直接从 `pydantic` 导入 `Field` 。

///

## 声明模型属性 { #declare-model-attributes }

然后，使用 `Field` 定义模型的属性：

 * Subclasses should override one or more methods to modify the behavior of the backing deque as
 * desired per the <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
 *
 * <p><b>Warning:</b> The methods of {@code ForwardingBlockingDeque} forward <b>indiscriminately</b>
 * to the methods of the delegate. For example, overriding {@link #add} alone <b>will not</b> change

   *   <li>{@linkplain LoadingCache#getAll bulk loading requests}, including {@linkplain
   *       CacheLoader#loadAll bulk loading implementations}
   * </ul>
   *
   * <p><b>Warning:</b> For any given key, every {@code loader} used with it should compute the same
   * value. Otherwise, a call that passes one {@code loader} may return the result of another call

			b.Fatal(err)
		}
	}
}

func TestEncodeDecodensScannerOptions(t *testing.T) {
	v := nsScannerOptions{}
	var buf bytes.Buffer
	msgp.Encode(&buf, &v)

	m := v.Msgsize()
	if buf.Len() > m {
		t.Log("WARNING: TestEncodeDecodensScannerOptions Msgsize() is inaccurate")
	}

	vn := nsScannerOptions{}
	err := msgp.Decode(&buf, &vn)
	if err != nil {
		t.Error(err)
	}

	buf.Reset()
	msgp.Encode(&buf, &v)

 *
 * <p><b>Warning:</b> The methods of {@code ForwardingFuture} forward <b>indiscriminately</b> to the
 * methods of the delegate. For example, overriding {@link #get(long, TimeUnit)} alone <b>will
 * not</b> change the behavior of {@link #get()}, which can lead to unexpected behavior. In this
 * case, you should override {@code get()} as well.
 *

 * override one or more methods to modify the behavior of the backing sorted map as desired per the
 * <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
 *
 * <p><b>Warning:</b> The methods of {@code ForwardingSortedMap} forward <i>indiscriminately</i> to
 * the methods of the delegate. For example, overriding {@link #put} alone <i>will not</i> change

     * {@link org.apache.maven.api.services.BuilderProblem.Severity#WARNING}. This check is logically equivalent
     * to "is there any problem reported?", given warning is the lowest severity.
     */
    default boolean hasWarningProblems() {
        return hasProblemsFor(BuilderProblem.Severity.WARNING);
    }

    /**

import static com.google.common.base.StandardSystemProperty.JAVA_CLASS_PATH;
import static com.google.common.base.StandardSystemProperty.PATH_SEPARATOR;
import static java.util.logging.Level.WARNING;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.CharMatcher;
import com.google.common.base.Splitter;
import com.google.common.collect.FluentIterable;

/// warning

This page hasn’t been translated into your language yet. 🌍

We’re currently switching to an automated translation system 🤖, which will help keep all translations complete and up to date.

Learn more: [Contributing - Translations](https://fastapi.tiangolo.com/contributing/#translations){.internal-link target=_blank}

			b.Fatal(err)
		}
	}
}

func TestEncodeDecodeBatchJobExpire(t *testing.T) {
	v := BatchJobExpire{}
	var buf bytes.Buffer
	msgp.Encode(&buf, &v)

	m := v.Msgsize()
	if buf.Len() > m {
		t.Log("WARNING: TestEncodeDecodeBatchJobExpire Msgsize() is inaccurate")
	}

	vn := BatchJobExpire{}
	err := msgp.Decode(&buf, &vn)
	if err != nil {
		t.Error(err)
	}

	buf.Reset()
	msgp.Encode(&buf, &v)