# Extra Models { #extra-models }

Continuing with the previous example, it will be common to have more than one related model.

This is especially the case for user models, because:

* The **input model** needs to be able to have a password.
* The **output model** should not have a password.
* The **database model** would probably need to have a hashed password.

/// danger

# Query Parameter Models { #query-parameter-models }

If you have a group of **query parameters** that are related, you can create a **Pydantic model** to declare them.

This would allow you to **re-use the model** in **multiple places** and also to declare validations and metadata for all the parameters at once. 😎

/// note

This is supported since FastAPI version `0.115.0`. 🤓

///

# Cookie Parameter Models { #cookie-parameter-models }

If you have a group of **cookies** that are related, you can create a **Pydantic model** to declare them. 🍪

This would allow you to **re-use the model** in **multiple places** and also to declare validations and metadata for all the parameters at once. 😎

/// note

This is supported since FastAPI version `0.115.0`. 🤓

///

/// tip

## Nested Models { #nested-models }

Each attribute of a Pydantic model has a type.

But that type can itself be another Pydantic model.

So, you can declare deeply nested JSON "objects" with specific attribute names, types and validations.

All that, arbitrarily nested.

### Define a submodel { #define-a-submodel }

For example, we can define an `Image` model:

///

## Pydantic Models for Forms { #pydantic-models-for-forms }

You just need to declare a **Pydantic model** with the fields you want to receive as **form fields**, and then declare the parameter as `Form`:

{* ../../docs_src/request_form_models/tutorial001_an_py310.py hl[9:11,15] *}

**FastAPI** will **extract** the data for **each field** from the **form data** in the request and give you the Pydantic model you defined.

# 額外的模型 { #extra-models }

延續前一個範例，通常會有不只一個彼此相關的模型。

對使用者模型尤其如此，因為：

* 「輸入模型」需要能包含密碼。
* 「輸出模型」不應包含密碼。
* 「資料庫模型」通常需要儲存雜湊後的密碼。

/// danger

切勿儲存使用者的明文密碼。務必只儲存可供驗證的「安全雜湊」。

若你還不清楚，稍後會在[安全性章節](security/simple-oauth2.md#password-hashing)學到什麼是「密碼雜湊」。

///

## 多個模型 { #multiple-models }

以下是模型大致長相、與其密碼欄位以及它們被使用的位置：

{* ../../docs_src/extra_models/tutorial001_py310.py hl[7,9,14,20,22,27:28,31:33,38:39] *}

# Body - 巢狀模型 { #body-nested-models }

使用 **FastAPI**，你可以定義、驗證、文件化，並使用任意深度的巢狀模型（感謝 Pydantic）。

## 列表欄位 { #list-fields }

你可以將屬性定義為某個子型別。例如，Python 的 `list`：

{* ../../docs_src/body_nested_models/tutorial001_py310.py hl[12] *}

這會讓 `tags` 成為一個列表，儘管尚未宣告列表元素的型別。

## 具有型別參數的列表欄位 { #list-fields-with-type-parameter }

不過，Python 有一種專門的方式來宣告具有內部型別（「型別參數」）的列表：

### 宣告帶有型別參數的 `list` { #declare-a-list-with-a-type-parameter }

# Header 参数模型 { #header-parameter-models }

如果您有一组相关的 **header 参数**，您可以创建一个 **Pydantic 模型**来声明它们。

这将允许您在**多个地方**能够**重用模型**，并且可以一次性声明所有参数的验证和元数据。😎

/// note | 注意

自 FastAPI 版本 `0.115.0` 起支持此功能。🤓

///

## 使用 Pydantic 模型的 Header 参数 { #header-parameters-with-a-pydantic-model }

在 **Pydantic 模型**中声明所需的 **header 参数**，然后将参数声明为 `Header` :

{* ../../docs_src/header_param_models/tutorial001_an_py310.py hl[9:14,18] *}

# Cookie 參數模型 { #cookie-parameter-models }

如果你有一組彼此相關的「**Cookie**」，你可以建立一個「**Pydantic 模型**」來宣告它們。🍪

這樣你就能在**多處**重複使用該模型，並且能一次性為所有參數宣告**驗證**與**中繼資料**。😎

/// note | 注意

自 FastAPI 版本 `0.115.0` 起支援。🤓

///

/// tip

同樣的技巧也適用於 `Query`、`Cookie` 與 `Header`。😎

///

## 以 Pydantic 模型宣告 Cookie { #cookies-with-a-pydantic-model }

在 **Pydantic 模型**中宣告所需的 **Cookie** 參數，接著將參數宣告為 `Cookie`：

# Header Parameter Models { #header-parameter-models }

If you have a group of related **header parameters**, you can create a **Pydantic model** to declare them.

This would allow you to **re-use the model** in **multiple places** and also to declare validations and metadata for all the parameters at once. 😎

/// note

This is supported since FastAPI version `0.115.0`. 🤓

///