# Jinja 模板

Jinja 是一个高效、功能强大的模板引擎，广泛用于生成动态内容。它允许在多种基于文本的格式（如 HTML、XML、CSV 或 LaTex）中嵌入编程逻辑。了解更多信息，请参阅：[Jinja 文档](https://jinja.palletsprojects.com/en/3.1.x/) 。

在现代数据工程中，Jinja 因为能够在 SQL 转换中支持变量、逻辑和重用性，已经成为一种流行的选择。

Recurve 支持在 SQL 模型中直接使用 Jinja。

## Jinja 语法

Jinja 的语法与 Python 类似，代码通常位于特定的分隔符标签内，主要包括以下几种：

* **表达式`{{ ... }}：`** 用于输出字符串、引用变量和调用宏。
* **语句`{% ... %}`**：用于控制流（如 `for` 循环和 `if` 语句），也用于定义宏。
* **注释`{# ... #}`**：注释内容，编译时会被忽略。

以下是一些在 Recurve SQL 模型中使用 Jinja 的示例。

**设置变量**

Recurve 支持创建全局变量，这些变量可以在多个模型和数据管道中重复使用。详情请查阅文档：[变量](/cn-reorc-help-center/advanced_usage/bian-liang.md)

{% tabs %}
{% tab title="SQL 模型" %}
在 Jinja 中，您可以按照以下方式定义局部变量：

```sql
-- min_rental_duration = 3, defined in the Variables section

SELECT film_id, title, rental_duration
FROM film
WHERE rental_duration >= {{ var('min_rental_duration') }}
```

{% endtab %}

{% tab title="编译代码" %}

```sql
SELECT film_id, title, rental_duration
FROM film
WHERE rental_duration >= 3
```

{% endtab %}
{% endtabs %}

`if` **语句**

{% tabs %}
{% tab title="SQL 模型" %}
用 `if` 语句来检查条件：

```sql
{% set include_r_rated = true %}

SELECT film_id, title, rating
FROM film
WHERE 1=1 
{% if include_r_rated %}
  AND rating = 'R'
{% else %}
  AND rating != 'R'
{% endif %}
```

{% endtab %}

{% tab title="编译代码" %}

```sql
SELECT film_id, title, rating
FROM film
WHERE 1=1

  AND rating = 'R'
```

{% endtab %}
{% endtabs %}

`for` **循环**

{% tabs %}
{% tab title="SQL 模型" %}
用 `for` 循环来遍历一个列表或字典：

```sql
{% set categories = ['Action', 'Comedy', 'Drama'] %}

SELECT f.film_id, f.title, c.name AS category
FROM film f
JOIN film_category fc ON f.film_id = fc.film_id
JOIN category c ON fc.category_id = c.category_id
WHERE c.name IN (
  {% for category in categories %}
    '{{ category }}'{% if not loop.last %},{% endif %}
  {% endfor %}
)
```

{% endtab %}

{% tab title="编译代码" %}

```sql
SELECT f.film_id, f.title, c.name AS category
FROM film f
JOIN film_category fc ON f.film_id = fc.film_id
JOIN category c ON fc.category_id = c.category_id
WHERE c.name IN ( 
    'Action',
    'Comedy',
    'Drama'
)
```

{% endtab %}
{% endtabs %}


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