///

### Pydantic v1 and v2 on the same app { #pydantic-v1-and-v2-on-the-same-app }

It's **not supported** by Pydantic to have a model of Pydantic v2 with its own fields defined as Pydantic v1 models or vice versa.

```mermaid
graph TB
    subgraph "❌ Not Supported"
        direction TB
        subgraph V2["Pydantic v2 Model"]
            V1Field["Pydantic v1 Model"]
        end

    public String createdTime;

    /** The version number for optimistic locking. */
    public String versionNo;

    /**
     * Clears all pagination and search criteria fields, resetting them to their default values.
     */
    public void clear() {
        allRecordCount = 0;
        allPageCount = 0;
        existPrePage = false;
        existNextPage = false;

 */

@NullUnmarked
@GwtIncompatible
@J2ktIncompatible
public class AbstractFutureFallbackAtomicHelperTest extends TestCase {

  // stash these in static fields to avoid loading them over and over again (speeds up test
  // execution significantly)

  /**
   * This classloader disallows {@link java.lang.invoke.VarHandle}, which will prevent us from

			return err
		}
	case !f.Tag.IsEmpty():
		if err := e.EncodeElement(f.Tag, xml.StartElement{Name: xml.Name{Local: "Tag"}}); err != nil {
			return err
		}
	default:
		// Always print Prefix field when both And & Tag are empty
		if err := e.EncodeElement(f.Prefix, xml.StartElement{Name: xml.Name{Local: "Prefix"}}); err != nil {
			return err
		}
	}

	return e.EncodeToken(xml.EndElement{Name: start.Name})
}

            addFieldToSource(sourceMap, "x121Address", x121Address);
        }
        return sourceMap;
    }

    protected void addFieldToSource(Map<String, Object> sourceMap, String field, Object value) {
        sourceMap.put(field, value);
    }

    // ===================================================================================
    //                                                                      Basic Override

     * purposes, the "count" field, tracking the number of elements, serves as that volatile
     * variable ensuring visibility. This is convenient because this field needs to be read in many
     * read operations anyway:
     *
     * - All (unsynchronized) read operations must first read the "count" field, and should not look
     * at table entries if it is 0.
     *

        try {
            var f = target.getClass().getDeclaredField(name);
            f.setAccessible(true);
            return f.get(target);
        } catch (Exception e) {
            fail("access field " + name, e);
            return null;
        }
    }

    private static int invokeProtectedInt(Object target, String name, Object... params) {
        try {
            var cls = target.getClass();

{* ../../docs_src/dataclasses_/tutorial003_py310.py hl[1,4,7:10,13:16,22:24,27] *}

1. Wir importieren `field` weiterhin von Standard-`dataclasses`.

2. `pydantic.dataclasses` ist ein direkter Ersatz für `dataclasses`.

3. Die Datenklasse `Author` enthält eine Liste von `Item`-Datenklassen.

In that case, you can simply swap the standard `dataclasses` with `pydantic.dataclasses`, which is a drop-in replacement:

{* ../../docs_src/dataclasses_/tutorial003_py310.py hl[1,4,7:10,13:16,22:24,27] *}

1. We still import `field` from standard `dataclasses`.

2. `pydantic.dataclasses` is a drop-in replacement for `dataclasses`.

3. The `Author` dataclass includes a list of `Item` dataclasses.

```JSON
{
  "detail": [
    {
      "type": "missing",
      "loc": [
        "query",
        "needy"
      ],
      "msg": "Field required",
      "input": null
    }
  ]
}
```

Оскільки `needy` є обов’язковим параметром, вам потрібно вказати його в URL:

```
http://127.0.0.1:8000/items/foo-item?needy=sooooneedy
```