就和宣告查詢參數時一樣，當模型屬性有預設值時，它就不是必填；否則就是必填。使用 `None` 可使其成為選填。

例如，上述模型對應的 JSON「`object`」（或 Python `dict`）如下：

```JSON
{
    "name": "Foo",
    "description": "An optional description",
    "price": 45.2,
    "tax": 3.5
}
```

...由於 `description` 與 `tax` 是選填（預設為 `None`），以下這個 JSON「`object`」也有效：

```JSON
{
    "name": "Foo",
    "price": 45.2
}
```

## 將它宣告為參數 { #declare-it-as-a-parameter }

nakijin.okinawa.jp
naklo.pl
nalchik.ru
nalchik.su
namaste.jp
namdalseid.no
namdinh.vn
name
name.az
name.eg
name.et
name.fj
name.hr
name.mk
name.mv
name.my
name.ng
name.pm
name.pr
name.qa
name.tj
name.tr
name.tt
name.vn
namegata.ibaraki.jp
namegawa.saitama.jp
namerikawa.toyama.jp
namie.fukushima.jp
namikata.ehime.jp

if "%FESS_MAX_MEM%" == "" (
set FESS_MAX_MEM=1g
)

if NOT "%FESS_HEAP_SIZE%" == "" (
set FESS_MIN_MEM=%FESS_HEAP_SIZE%
set FESS_MAX_MEM=%FESS_HEAP_SIZE%
)

REM min and max heap sizes should be set to the same value to avoid
REM stop-the-world GC pauses during resize, and so that we can lock the
REM heap in memory on startup to prevent any of it from being swapped
REM out.

* **output** için **required olur** (ve `None` olabilir; JSON açısından `null`)

### Dokümanlarda Output Modeli { #model-for-output-in-docs }

Dokümanlarda output modelini de kontrol edebilirsiniz; **hem** `name` **hem de** `description` alanları **kırmızı yıldız** ile **required** olarak işaretlenmiştir:

<div class="screenshot">
<img src="/img/tutorial/separate-openapi-schemas/image03.png">
</div>

Por exemplo, você poderia ter um arquivo `main.py` com:

```Python hl_lines="3"
import os

name = os.getenv("MY_NAME", "World")
print(f"Hello {name} from Python")
```

/// tip | Dica

O segundo argumento para [`os.getenv()`](https://docs.python.org/3.8/library/os.html#os.getenv) é o valor padrão a ser retornado.

    // ===================================================================================
    //                                                                       Name Override
    //                                                                       =============
    @Override
    public String asTableDbName() {
        return "duplicate_host";
    }

    @Override

    // ===================================================================================
    //                                                                       Name Override
    //                                                                       =============
    @Override
    public String asTableDbName() {
        return "failure_url";
    }

    @Override

    // ===================================================================================
    //                                                                       Name Override
    //                                                                       =============
    @Override
    public String asTableDbName() {
        return "key_match";
    }

    @Override

type ExcludedPrefix struct {
	Prefix string
}

// Versioning - Configuration for bucket versioning.
type Versioning struct {
	XMLNS   string   `xml:"xmlns,attr,omitempty"`
	XMLName xml.Name `xml:"VersioningConfiguration"`
	// MFADelete State    `xml:"MFADelete,omitempty"` // not supported yet.
	Status State `xml:"Status,omitempty"`
	// MinIO extension - allows selective, prefix-level versioning exclusion.

		if value != "" {
			if tagString != "" {
				tagString += ", "
			}
			tagString += fmt.Sprintf("%s=%#v", key, value)
		}
	}

	var apiString string
	if entry.API != nil {
		apiString = "API: " + entry.API.Name
		if entry.API.Args != nil {
			args := ""
			if entry.API.Args.Bucket != "" {
				args = args + "bucket=" + entry.API.Args.Bucket
			}
			if entry.API.Args.Object != "" {