Detailed explanation of the implementation method of PHP loop query subcategory

PHP loop query subcategory is a requirement often encountered in website development, especially when building product classification, news classification and other systems. This article will introduce in detail how to use PHP to implement loop query subcategories and provide specific code examples.

1. Basic idea

Generally speaking, product classification or news classification systems are organized in a tree structure, that is, there can be multiple sub-categories under one category, and each sub-category can has its own subcategory, and so on. Therefore, we need to traverse the subcategories under each parent category, and then recursively query the subcategories under each subcategory until the entire classification tree is traversed.

2. Implementation method

The following is a simple PHP function that can query all subcategories under a certain category:

function getSubCategories($parentId, $categories) {
    $subCategories = array();
    
    foreach ($categories as $category) {
        if ($category['parent_id'] == $parentId) {
            $subCategories[] = $category;
            $subCategories = array_merge($subCategories, getSubCategories($category['id'], $categories));
        }
    }
    
    return $subCategories;
}

// 假设 $categories 是一个包含所有分类信息的数组
$parentId = 1; // 查询父分类为1的所有子分类
$subCategories = getSubCategories($parentId, $categories);

foreach ($subCategories as $subCategory) {
    echo $subCategory['name'] . PHP_EOL;
}

3. Code analysis

• getSubCategories The function accepts two parameters, which are the parent category ID to be queried and an array containing all category information.
• The function first initializes an empty array $subCategories, which is used to save all the queried subcategories.
• Then loop through the $categories array through foreach, if the parent_id of a category is equal to the passed in $parentId, then add the category to the $subCategories array, and recursively call the getSubCategories function to continue querying the subcategories of the category.
• Finally returns an array containing all subcategories $subCategories.
• In the main program, we can call the getSubCategories function by specifying the ID of the parent category to get the array of all subcategories and perform subsequent processing.

4. Summary

Through the above code examples, we can realize the function of querying subcategories in a loop in PHP. This method is suitable for various scenarios that require querying tree-structured data, such as product classification, news classification, regional classification, etc. In actual applications, the code can be improved and expanded according to specific needs to better meet the needs of the project.

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