我想在具有树结构的选择框中显示类别列表（多级子类别）
类似这样：
-electronic
--camera
---sumsung
---- other subcategory
---- ...
---lg
-art
表结构：
+----+------------+-----------+
| id | name | parent_id |
+----+------------+-----------+
| 1 | electronic | 0 |
+----+------------+-----------+
| 2 | arts | 0 |
+----+------------+-----------+
| 3 | camera | 1 |
+----+------------+-----------+
| 4 | sumsung | 3 |
+----+------------+-----------+
| 4 | lg | 3 |
+----+------------+-----------+
类别型号：
public function children()
{
return $this->hasMany(self::class, 'parent_id', 'id');
}
public function parent()
{
return $this->belongsTo(self::class, 'parent_id');
}
这仅返回类别和 1 级子类别
<select>
@foreach($data as $categories)
<optgroup label="{{ $categories->name }}">
@foreach($categories->children as $category)
<option value="{{ $category->id }}">{{ $category->name }}</option>
@endforeach
</optgroup>
@endforeach
</select>
如何显示多级子类别？
好吧，在这里我没有按照您的方法将类别放入选择框中，而是选择通过嵌套无序列表来描述它，但您也可以找到一种方法使其在选择框中也适用。
要解决多级类别渲染，您可以使用递归方法。在这里，我创建了一个blade模板文件，即categories.blade.php，代码如下：
类别.blade.php
<!-- Displaying the current category -->
<li value="{{ $category->id }}">{{ $category->name}}
<!-- If category has children -->
@if (count($category->children) > 0)
<!-- Create a nested unordered list -->
<ul>
<!-- Loop through this category's children -->
@foreach ($category->children as $sub)
<!-- Call this blade file again (recursive) and pass the current subcategory to it -->
@include('subcategories', ['category' => $sub])
@endforeach
</ul>
@endif
</li>
现在，在您的父刀片模板文件中，您可以包含categories.blade.php 文件，以循环遍历您的类别并显示它们。
...
<!-- Start an unoredered list -->
<ul>
<!-- Loop through each category -->
@foreach ($categories as $category)
<!-- Include subcategories.blade.php file and pass the current category to it -->
@include('subcategories', ['category' => $category])
@endforeach
<ul>
...
Here is an example that worked for me using the above technique: 
Note 1:根据我的示例，假设categories.blade.php文件和父刀片文件位于同一文件夹中，如果您决定将它们放在不同的文件夹中，请确保在@include语句中输入正确的路径父刀片文件。
Note 2:据此：https://www.w3.org/TR/html401/interact/forms.html#h-17.6 https://www.w3.org/TR/html401/interact/forms.html#h-17.6，你不能嵌套optgroup标签相互嵌套，所以我建议您找到另一种方式来显示选择框。