{* ../../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.

...без додавання обов’язкового параметра `needy`, Ви побачите помилку:

```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
```

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

As `needy` is a required parameter, you would need to set it in the URL:

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

					return
				}
			case schema.Many2Many:
				var (
					queryConds     = make([]clause.Expression, 0, len(rel.References))
					foreignFields  = make([]*schema.Field, 0, len(rel.References))
					relForeignKeys = make([]string, 0, len(rel.References))
					modelValue     = reflect.New(rel.JoinTable.ModelType).Interface()
					table          = rel.JoinTable.Table

// migration failed to capture '.This' field properly which indicates
// the disk UUID association. Below error message is returned when
// we see this situation in format.json, for more info refer
// https://github.com/minio/minio/issues/5667
var errErasureV3ThisEmpty = fmt.Errorf("Erasure format version 3 has This field empty")

// isServerResolvable - checks if the endpoint is resolvable

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

Поскольку `needy` является обязательным параметром, вам необходимо указать его в URL-адресе:

```

find the definition of xxx.  If xxx is a type, cgo replaces C.xxx with
a Go translation.  C arithmetic types translate to precisely-sized Go
arithmetic types.  A C struct translates to a Go struct, field by
field; unrepresentable fields are replaced with opaque byte arrays.  A
C union translates into a struct containing the first union member and
perhaps additional padding.  C arrays become Go arrays.  C pointers

* `table=True` sagt SQLModel, dass dies ein *Tabellenmodell* ist, es soll eine **Tabelle** in der SQL-Datenbank darstellen, es ist nicht nur ein *Datenmodell* (wie es jede andere reguläre Pydantic-Klasse wäre).

* `Field(primary_key=True)` sagt SQLModel, dass die `id` der **Primärschlüssel** in der SQL-Datenbank ist (Sie können mehr über SQL-Primärschlüssel in der SQLModel-Dokumentation erfahren).

Этого можно добиться, используя <a href="https://docs.pydantic.dev/latest/concepts/validators/#field-after-validator" class="external-link" target="_blank">`AfterValidator` Pydantic</a> внутри `Annotated`.

/// tip | Совет

В Pydantic также есть <a href="https://docs.pydantic.dev/latest/concepts/validators/#field-before-validator" class="external-link" target="_blank">`BeforeValidator`</a> и другие. 🤓

///