[Summary sharing] Efficient PHP loop query subcategory method

In the field of Web development, classification query is a very common requirement. Whether it is an e-commerce platform or a content management system, there is a data display method based on classification. As the number of classification layers increases, the task of querying sub-categories becomes more and more complex. This article will introduce an efficient PHP loop query method for subcategories to help developers easily manage category hierarchies.

1. Get classified data

First, we need to get classified data. Here we take a simple database table as an example. Assume that this table is named category and has the following fields:

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id	name	parent_id
1	household appliances	0

Among them, id is the unique identifier of the category, name is the category name, and parent_id is the parent to which the category belongs. The id of the category. If the category has no parent category, parent_id is 0.

2. Create query function

Next, we can create a query function that will receive the id of a parent category as a parameter, And returns all subcategories under the parent category.

function get_children_categories($parent_id) {

// <code to query categories from database by parent_id>

return $categories;

}

In the above code, we will query all subcategories from the database and return them for our further use.

3. Constructing a recursive query method

For situations with multiple levels of sub-categories, we need a recursive query method. That is, we need to recursively query downwards starting from the root node until we find the required subcategory.

The specific code implementation is as follows:

function get_children_categories($parent_id) {

$categories = array();

// <code to query categories from database by parent_id>

foreach($results as $result) {

$category = array();

$category['id'] = $result['id'];
$category['name'] = $result['name'];

$children = get_children_categories($result['id']);
if (!empty($children)) {
$category['children'] = $children;
}

$categories[] = $category;

}

return $categories;

}

The above code recursively queries the subcategories of each category layer by layer and adds them to the result set, thereby building a complete classification hierarchy. In this process, we will use PHP's foreach loop and recursively call our own methods.

4. Traversing subcategories

Now that we have successfully obtained a complete category hierarchy, we can iterate through them using a foreach loop.

function print_categories($categories) {

echo "<ul>";

foreach($categories as $category) {

echo "<li>" . $category['name'] . "</li>";

if (!empty($category['children'])) {
print_categories($category['children']);
}

}

echo "</ul>";

}

Here, we will traverse each category and output their names. If the category contains subcategories, call your own method recursively and print out all subcategories.

5. Performance considerations

During the implementation of the above code, we took the performance of the code into consideration. Especially for classification hierarchies with a large number of sub-categories, you may encounter performance bottlenecks when querying recursively. In order to solve this problem, we can use a caching mechanism to cache the results in memory to improve query speed. Here, we can use PHP's memcached extension to cache the result set in memory, and obtain the results directly from the cache in subsequent queries.

$memcached = new Memcached();

$memcached->addServer('localhost', 11211);

$categories = $memcached->get('categories:1');

if (!$categories) {

$categories = get_children_categories(1);

$memcached->set('categories:1', $categories);

}

print_categories($categories);

In the above code, we first established a memcached client connection and cached the classification results into the cache key named "categories:1". In subsequent queries, we can get the results directly from the cache without re-executing the query function. This approach can significantly improve query performance, especially for large-scale categorical data.

6. Summary

This article introduces an efficient method of querying subcategories in a PHP loop. By recursively querying subcategories layer by layer and using the caching mechanism, we can easily manage the classification hierarchy, improve query efficiency, and provide a more convenient classification query method for Web development.

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