How to use PHP to implement multi-level classification and tree structures

How to use PHP to implement multi-level classification and tree structure

When developing web applications, we often encounter situations where we need to classify data at multiple levels. For example, product classification, article classification, etc. Displaying these categories in a tree structure can intuitively reflect the hierarchical relationship of the categories, making it easier for users to browse and manage. This article will introduce how to use PHP to implement multi-level classification and tree structures.

1. Database design
First, you need to design a database table to store classified data. Suppose we have a classification table containing the following fields:

• id: the unique identifier of the classification
• name: the name of the classification
• parent_id: the parent classification id, if it is a first-level classification, the parent_id is 0

2. Model class
We need to create a model class to interact with the database. This model class will include the following basic operations:

• Get all categories: Get all category data from the database
• Get sub-categories based on parent id: Get the corresponding sub-category data based on parent id from the database
• Get a single category based on id: Get the corresponding category data from the database based on id
• Create category: Insert new category data into the database
• Update category: Update the category data in the database
• Delete category: delete the specified category data from the database

The following is a simple sample code of the CategoryModel class:

class CategoryModel {
    // 获取所有分类
    public function getAllCategories() {
        // 连接数据库，执行 SQL 查询获取数据
        // 返回分类数据数组
    }
    
    // 根据父级 id 获取子分类
    public function getChildCategories($parentId) {
        // 连接数据库，执行 SQL 查询获取数据
        // 返回子分类数据数组
    }
    
    // 根据 id 获取单个分类
    public function getCategoryById($id) {
        // 连接数据库，执行 SQL 查询获取数据
        // 返回单个分类数据
    }
    
    // 创建分类
    public function createCategory($name, $parentId) {
        // 连接数据库，执行 SQL 插入操作
        // 返回新创建分类的 id
    }
    
    // 更新分类
    public function updateCategory($id, $name, $parentId) {
        // 连接数据库，执行 SQL 更新操作
        // 返回更新是否成功的标识
    }
    
    // 删除分类
    public function deleteCategory($id) {
        // 连接数据库，执行 SQL 删除操作
        // 返回删除是否成功的标识
    }
}

3. Build a tree structure
We can use recursion to build a tree structure. First, we obtain the first-level classification data from the database, and then perform recursive operations on each first-level classification to obtain its subordinate classifications and build a complete tree structure.

The following is a sample code for building a tree structure:

class CategoryTree {
    // 递归构建树状结构
    public function buildTree($parentId = 0) {
        // 获取子分类
        $childCategories = $this->categoryModel->getChildCategories($parentId);
        
        // 遍历子分类
        foreach ($childCategories as $category) {
            // 创建节点
            $node = new TreeNode($category->id, $category->name);
            
            // 递归构建子树
            $node->children = $this->buildTree($category->id);
            
            // 添加节点到根节点
            $this->root->addChild($node);
        }
        
        // 返回根节点
        return $this->root;
    }
}

class TreeNode {
    public $id;
    public $name;
    public $children = array();
    
    public function __construct($id, $name) {
        $this->id = $id;
        $this->name = $name;
    }
    
    // 添加子节点
    public function addChild($child) {
        $this->children[] = $child;
    }
}

4. Usage example
The following is a usage example based on the above model class and tree structure:

// 创建分类模型实例
$categoryModel = new CategoryModel();

// 创建树状结构实例
$tree = new CategoryTree();

// 获取所有分类数据
$categories = $categoryModel->getAllCategories();

// 遍历分类数据，初始化根节点
foreach ($categories as $category) {
    if ($category->parent_id == 0) {
        $tree->root = new TreeNode($category->id, $category->name);
        break;
    }
}

// 构建树状结构
$tree->buildTree();

// 打印树状结构
echo json_encode($tree->root, JSON_PRETTY_PRINT);

The above sample code is just a basic implementation example. In actual applications, it may need to be modified and expanded according to specific needs to meet actual needs.

Summary
This article introduces how to use PHP to implement multi-level classification and tree structure, and gives corresponding code examples. By building a tree structure, we can easily display and manage categories, allowing users to intuitively understand the hierarchical relationships between categories. I hope this article can help readers better understand and apply multi-level classification and tree structures.

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