问题
First of all, I posted another question about this, but didn't get answer so I needed to post a new one.
I have a function which is listing categories hierarchically, I created another function (on same function) with foreach loop in, and using it into dropdowns too, so don't need to create another query, using my existing function multiple times.
I want to use same query to list subcategories under a selected category.
Example: if category.php?id=100 clicked, then I want to list subcategories under catgeory 100 hierarchicaly in landing page.
Here is my function :
$allCategories = array();
$categoryMulti = array(
'categories' => array(),
'parent_cats' => array()
);
while ($row = $stmt->fetch()) {
//I created another array to get subcats didnt work
//$categories['categories'][1]
$categoryMulti['categories'][$row['cat_id']] = $row;
$categoryMulti['parent_cats'][$row['parent_id']][] = $row['cat_id'];
$allCategories[] = $row;
}
function listCategoryTree($parent, $category)
{
$html = "";
if (isset($category['parent_cats'][$parent])) {
$html .= "<ul>\n";
foreach
($category['parent_cats'][$parent] as $cat_id) {
if (!isset($category['parent_cats'][$cat_id])) {
$html .= "<li>" . $category['categories'][$cat_id]['cat_name'] . "</li>";
} else {
$html .= "<li>" . $category['categories'][$cat_id]['cat_name'];
$html .= listCategoryTree($cat_id, $category);
$html .= "</li>";
}
}
$html .= "</ul> \n";
}
return $html;
}
Usage : echo listCategoryTree(0, $categoryMulti);
And here is how I use in dropdown showing just for an example it works fine:
function selectCategories($categories)
{
foreach ($categories as $category) {
echo '<option value="' . $category['cat_id'] . '">' . $category['cat_name'] . '</option>';
}
}
selectCategories($allCategories);
And this is one of the examples that i tried to make it work with the selected category method, but unfortunately, it didn't worked.
I created a new array in my function:
$subCategories = array();
$subCategories[] = $row;
And call it as a function like following but didn't work.
function cats($categories)
{
foreach($categories as $category) {
echo '<ul>';
echo '<li>' . $category['cat_name'] . '</li>';
echo '</ul>';
}
}
echo cats(100, $subCategories);
回答1:
There are a couple of solutions. First of all, I'll use the following data (categories table) as an example.
+----+--------------------------+-----------+
| id | name | parent_id |
+----+--------------------------+-----------+
| 1 | Electronics | NULL |
| 2 | Apparel & Clothing | NULL |
| 3 | Phones & Accessories | 1 |
| 4 | Computer & Office | 1 |
| 5 | Men's Clothing | 2 |
| 6 | Women's Clothing | 2 |
| 7 | Cell Phones | 3 |
| 8 | Cell Phone Accessories | 3 |
| 9 | Phone Parts | 3 |
| 10 | Computers & Accessories | 4 |
| 11 | Tablets & Accessories | 4 |
| 12 | Computer Peripherals | 4 |
| 13 | Computer Components | 4 |
| 14 | Office Electronics | 4 |
+----+--------------------------+-----------+
Solution 1 (Adjacency List):
You can easily fetch either all categories or subcategories of a category in a single query using WITH (Common Table Expressions) clause (requires MySQL 8.0):
// Database connection
$options = [
PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
PDO::ATTR_EMULATE_PREPARES => false,
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
];
$pdo = new PDO('mysql:host=localhost;dbname=<DATABASE_NAME>', '<USERNAME>', '<PASSWORD>', $options);
function getCategories(PDO $db, $parentId = null)
{
$sql = $parentId ? 'WITH RECURSIVE cte (id, name, parent_id) AS (SELECT id, name, parent_id FROM categories WHERE parent_id = ? UNION ALL SELECT c.id, c.name, c.parent_id FROM categories c INNER JOIN cte ON c.parent_id = cte.id) SELECT * FROM cte' : 'SELECT * FROM categories';
$stmt = $db->prepare($sql);
$stmt->execute($parentId ? [$parentId] : null);
return $stmt->fetchAll();
}
If you're using MySQL 5.7, change that function like so:
function getCategories(PDO $db, $parentId = null)
{
$sql = $parentId ? 'SELECT id, name, parent_id FROM (SELECT * FROM categories ORDER BY parent_id, id) c, (select @pv := ?) initialisation WHERE find_in_set(parent_id, @pv) AND LENGTH(@pv := concat(@pv, ",", id))' : 'SELECT * FROM categories';
$stmt = $db->prepare($sql);
$stmt->execute($parentId ? [$parentId] : null);
return $stmt->fetchAll();
}
To get all categories in your database:
$allCategories = getCategories($pdo);
Output:
+----+--------------------------+-----------+
| id | name | parent_id |
+----+--------------------------+-----------+
| 1 | Electronics | NULL |
| 2 | Apparel & Clothing | NULL |
| 3 | Phones & Accessories | 1 |
| 4 | Computer & Office | 1 |
| 5 | Men's Clothing | 2 |
| 6 | Women's Clothing | 2 |
| 7 | Cell Phones | 3 |
| 8 | Cell Phone Accessories | 3 |
| 9 | Phone Parts | 3 |
| 10 | Computers & Accessories | 4 |
| 11 | Tablets & Accessories | 4 |
| 12 | Computer Peripherals | 4 |
| 13 | Computer Components | 4 |
| 14 | Office Electronics | 4 |
+----+--------------------------+-----------+
To get subcategories of a category:
$subCategories = getCategories($pdo, 1); // 1 is parent_id
Output:
+----+--------------------------+-----------+
| id | name | parent_id |
+----+--------------------------+-----------+
| 3 | Phones & Accessories | 1 |
| 4 | Computer & Office | 1 |
| 7 | Cell Phones | 3 |
| 8 | Cell Phone Accessories | 3 |
| 9 | Phone Parts | 3 |
| 10 | Computers & Accessories | 4 |
| 11 | Tablets & Accessories | 4 |
| 12 | Computer Peripherals | 4 |
| 13 | Computer Components | 4 |
| 14 | Office Electronics | 4 |
+----+--------------------------+-----------+
If you want an HTML output, you can loop through $allCategories / $subCategories (based on your example):
function prepareCategories(array $categories)
{
$result = [
'all_categories' => [],
'parent_categories' => []
];
foreach ($categories as $category) {
$result['all_categories'][$category['id']] = $category;
$result['parent_categories'][$category['parent_id']][] = $category['id'];
}
return $result;
}
function buildCategories($categories, $parentId = null)
{
if (!isset($categories['parent_categories'][$parentId])) {
return '';
}
$html = '<ul>';
foreach ($categories['parent_categories'][$parentId] as $cat_id) {
if (isset($categories['parent_categories'][$cat_id])) {
$html .= "<li><a href='#'>{$categories['all_categories'][$cat_id]['name']}</a>";
$html .= buildCategories($categories, $cat_id);
$html .= '</li>';
} else {
$html .= "<li><a href='#'>{$categories['all_categories'][$cat_id]['name']}</a></li>";
}
}
$html .= '</ul>';
return $html;
}
echo buildCategories(prepareCategories($allCategories));
Output:
echo buildCategories(prepareCategories($subCategories), 1);
Output:
Solution 2 (Nested Sets):
We'll add additional columns left and right to our table and put numbers in it which will identify the groups belonging to the parent. (Note that we won't be using parent_id column.)
+----+--------------------------+--------------------------+
| id | name | parent_id | left | right |
+----+--------------------------+--------------------------+
| 1 | Electronics | NULL | 1 | 22 |
| 2 | Apparel & Clothing | NULL | 23 | 28 |
| 3 | Phones & Accessories | 1 | 2 | 9 |
| 4 | Computer & Office | 1 | 10 | 21 |
| 5 | Men's Clothing | 2 | 24 | 25 |
| 6 | Women's Clothing | 2 | 26 | 27 |
| 7 | Cell Phones | 3 | 3 | 4 |
| 8 | Cell Phone Accessories | 3 | 5 | 6 |
| 9 | Phone Parts | 3 | 7 | 8 |
| 10 | Computers & Accessories | 4 | 11 | 12 |
| 11 | Tablets & Accessories | 4 | 13 | 14 |
| 12 | Computer Peripherals | 4 | 15 | 16 |
| 13 | Computer Components | 4 | 17 | 18 |
| 14 | Office Electronics | 4 | 19 | 20 |
+----+--------------------------+--------------------------+
Now, we need to change our function:
function getCategories(PDO $db, $parentId = null)
{
$sql = $parentId ? 'SELECT children.* FROM categories parent INNER JOIN categories children ON parent.left < children.left AND parent.right > children.left WHERE parent.id = ?' : 'SELECT * FROM categories';
$stmt = $db->prepare($sql);
$stmt->execute($parentId ? [$parentId] : null);
return $stmt->fetchAll();
}
To get all categories in your database:
$allCategories = getCategories($pdo);
Output:
+----+--------------------------+--------------------------+
| id | name | parent_id | left | right |
+----+--------------------------+--------------------------+
| 1 | Electronics | NULL | 1 | 22 |
| 2 | Apparel & Clothing | NULL | 23 | 28 |
| 3 | Phones & Accessories | 1 | 2 | 9 |
| 4 | Computer & Office | 1 | 10 | 21 |
| 5 | Men's Clothing | 2 | 24 | 25 |
| 6 | Women's Clothing | 2 | 26 | 27 |
| 7 | Cell Phones | 3 | 3 | 4 |
| 8 | Cell Phone Accessories | 3 | 5 | 6 |
| 9 | Phone Parts | 3 | 7 | 8 |
| 10 | Computers & Accessories | 4 | 11 | 12 |
| 11 | Tablets & Accessories | 4 | 13 | 14 |
| 12 | Computer Peripherals | 4 | 15 | 16 |
| 13 | Computer Components | 4 | 17 | 18 |
| 14 | Office Electronics | 4 | 19 | 20 |
+----+--------------------------+--------------------------+
To get subcategories of a category:
$subCategories = getCategories($pdo, 1); // 1 is parent_id
Output:
+----+--------------------------+--------------------------+
| id | name | parent_id | left | right |
+----+--------------------------+--------------------------+
| 3 | Phones & Accessories | 1 | 2 | 9 |
| 4 | Computer & Office | 1 | 10 | 21 |
| 7 | Cell Phones | 3 | 3 | 4 |
| 8 | Cell Phone Accessories | 3 | 5 | 6 |
| 9 | Phone Parts | 3 | 7 | 8 |
| 10 | Computers & Accessories | 4 | 11 | 12 |
| 11 | Tablets & Accessories | 4 | 13 | 14 |
| 12 | Computer Peripherals | 4 | 15 | 16 |
| 13 | Computer Components | 4 | 17 | 18 |
| 14 | Office Electronics | 4 | 19 | 20 |
+----+--------------------------+--------------------------+
You can render HTML as shown in Solution 1. Read more about updating and inserting new data in nested set model.
Sources & Reads:
- Managing hierarchical data in MySQL - nested set
- Managing Hierarchical Data in MySQL
- Models for hierarchical data
- Managing Hierarchical Data in MySQL Using the Adjacency List Model
- Adjacency list vs. nested sets: MySQL
- One more Nested Intervals vs. Adjacency List comparison
来源：https://stackoverflow.com/questions/59334057/how-to-select-subcategories-from-selected-category-using-a-nested-function-in-ph