以正确的顺序让父母递归从MySQL表中删除

Question

I have an table structure like this

mysql> SELECT id, name, parent_id FROM categories;
+-------+------------+-----------+
| id    | name       | parent_id |
+-------+------------+-----------+
| 15790 | Test       |         0 |
| 15791 | Test2      |         0 |
| 16079 | Subtest    |     15790 |
| 16080 | Subtest 2  |     15790 |
| 16081 | Subsubtest |     16079 |
+-------+------------+-----------+

Now I want to look up the parent for every children and sibling and give it back in the right order for deletion.

So my output in this case would be:

Array
(
  16081,
  16080,
  16079,
  15791,
  15790
)

I can't delete just by reversing the parent ids, because this should be solid walking back the tree.

Also I am not able/allowed to change the structure of the table. So building kind of an index is necessary.

Answer 1

Assuming you don't have access to TRUNCATE , SET (so you could do SET FOREIGN_KEY_CHECKS=0; ), ALTER , etc. etc., and absolutely must use a script:

Since the question is tagged with php , this should do the trick:

function reversetree($src_arr, $currentid = 0)
{
    $cats = array();
    foreach($src_arr as $id => $parent)
    {   
        if($parent == $currentid)
        {
            $cats[] = $id;
            $cats = array_merge($cats, reversetree($src_arr, $id));
        }
    }
    return !$currentid ? array_reverse($cats) : $cats;
}

$rs = array();
foreach($pdo->query('SELECT id, parent_id FROM categories') as $row)
    $rs[$row['id']] = $row['parent_id'];

$stmt = $pdo->prepare('DELETE FROM categories WHERE id = ?');

$pdo->beginTransaction();
foreach(reversetree($rs) as $v)
    $stmt->execute(array($v));
$pdo->commit();

Answer 2

I don't understand why you need the IDs in a particular order. You can delete them with a transaction and they will all be deleted simultaneously.

DELETE FROM categories WHERE ID IN (15790,15791,16079,16080,16081);

Answer 3

You could add FOREIGN KEY constraint with CASCADE on DELETE. The foreign key will point to the same table on the parent id field.

When you delete the parent, all the children (no matter what level) are removed automatically.

Answer 4

<?php

// housekeeping
$pdo = new PDO($dsn, $user, $password);
$select = $pdo->prepare(
    "SELECT parent.id AS parent_id, child.id AS child_id
    FROM categories AS parent
    JOIN categories AS child ON parent.id = child.parent_id
    WHERE parent.id = ?"
);
$delete = $pdo->prepare('DELETE FROM categories WHERE id = ?');

// deletes $node_id, deletes its children first if required
function delete_node($node_id){
    $select->execute( array($node_id) );
    $children = $select->fetchAll(PDO::FETCH_NUM);
    if (count($children) !== 0) { // if 0, then the category does not exist, or it has no child
        foreach ($children as $child) { // call delete_node() recursively on each child
            delete_node ($child[1]);
        }
    }
    $delete->execute( array($node_id) ); // then delete this node (or do nothing if $node_id does not exist)
}


// to delete one category and all its sub-categories

delete_node(15790);

// to delete all contents

$allTopLevel = $pdo->exec('SELECT id FROM categories WHERE parent_id = 0')->fetchAll(PDO::FETCH_NUM);
foreach ($allTopLevel as $node) {
    delete_node($node[0]);
}

Not tested, not even sure if it "compiles", but you get the idea. Make sure to lock the table (or start a transaction) before calling delete_node() .

Answer 5

Sorry, i can't help much, because SQL is not my thing. But perhaps someone could transfer java pseudo code to the solution

delete(table.getFirstRow().get(id));

delete(id_a){
    for(data_set : table)
        if(data_set.get(parent_id) == id_a)delete(data_set.get(id));
    }
    table.remove(id_a);
}

edit: no iteration about elements? So something like this?

delete(list){
    if(list.size() == 0)return;
    idList = list.getAll(id);
    plist = table.getAllWhichEquals(parent_id, idList);
    delete(plist);
    table.remove(idList);
}

ah, forget it, i'm deleting not all at the same time, was just a try ^^