[英]How to convert this MPTT array into a tree structure in PHP?
我在数据库中有分层数据,以Modified Preorder Tree Traversal格式存储。 我在一个看起来类似“SELECT ID, Left
, Right
,Name等FROM FROM ORDER BY Left
;”的查询中提取数据。 我试图将这个数据从一个平面数组转换成DB给我一个树结构,然后我将用PHP的json_encode函数输出为JSON。
但是,我无法让我的树形结构代码超出第一级。 这是一个最小的测试用例:
<pre><?php
function projectListToTree($projects) {
$stack = Array();
for($x =0; $x < count($projects); $x++) {
$project = $projects[$x];
$project['Children'] = Array();
while(count($stack) > 0 && $stack[count($stack) - 1]['Right'] < $project['Right']) {
array_pop($stack);
}
if(count($stack) > 0) {
$stack[count($stack) - 1]['Children'][] = $project;
echo "Adding " . $project['Name'] . " to " . $stack[count($stack) - 1]['Name'] . " for a total of "
. count($stack[count($stack) - 1]['Children']) . " kids\n";
} else {
echo "No parent\n";
}
echo "stack count: " . count($stack) . "\n";
array_push($stack, $project);
}
echo "Left in stack: " . count($stack) . "\n";
return $stack[0];
}
/*
This is basically what comes from the DB.
Should be:
Parent
First Child
Second Child
Grand Child
*/
$projects = Array(
Array(
"ID" => "2",
"Left" => "2",
"Right" => "9",
"ParentID" => "1",
"Name" => "Parent"
),
Array(
"ID" => "3",
"Left" => "3",
"Right" => "4",
"ParentID" => "2",
"Name" => "First Child"
),
Array(
"ID" => "4",
"Left" => "5",
"Right" => "8",
"ParentID" => "2",
"Name" => "Second Child"
),
Array(
"ID" => "5",
"Left" => "6",
"Right" => "7",
"ParentID" => "4",
"Name" => "Grand Child"
)
);
$tree = projectListToTree($projects);
echo "-----\n\n\n\n";
var_dump($tree);
?></pre>
这就是我得到的输出:
No parent
stack count: 0
Adding First Child to Parent for a total of 1 kids
stack count: 1
Adding Second Child to Parent for a total of 2 kids
stack count: 1
Adding Grand Child to Second Child for a total of 1 kids
stack count: 2
Left in stack: 3
-----
array(6) {
["ID"]=>
string(1) "2"
["Left"]=>
string(1) "2"
["Right"]=>
string(1) "9"
["ParentID"]=>
string(1) "1"
["Name"]=>
string(6) "Parent"
["Children"]=>
array(2) {
[0]=>
array(6) {
["ID"]=>
string(1) "3"
["Left"]=>
string(1) "3"
["Right"]=>
string(1) "4"
["ParentID"]=>
string(1) "2"
["Name"]=>
string(11) "First Child"
["Children"]=>
array(0) {
}
}
[1]=>
array(6) {
["ID"]=>
string(1) "4"
["Left"]=>
string(1) "5"
["Right"]=>
string(1) "8"
["ParentID"]=>
string(1) "2"
["Name"]=>
string(12) "Second Child"
["Children"]=>
array(0) {
}
}
}
}
正如你所看到的,即使projectListToTree函数中的输出似乎表明它应该存在,某个地方“孙子”也会迷路。 看起来我抛出的任何树形结构都会降低第二级以下的任何结构。 对可能发生的事情的任何见解?
谢谢!
问题是分配数组不会复制引用,而是复制数组。 这意味着,您在“父”节点的“子”中拥有的“第二个子”数组与您添加“孙子”的数组不同,而是它的副本。
要解决此问题,您必须显式使用引用分配而不是复制:
function projectListToTree($projects) {
$stack = Array();
for($x =0; $x < count($projects); $x++) {
$project = &$projects[$x];
$project['Children'] = array();
while(count($stack) > 0 && $stack[count($stack) - 1]['Right'] < $project['Right']) {
array_pop($stack);
}
if(count($stack) > 0) {
$stack[count($stack) - 1]['Children'][] = &$project;
echo "Adding " . $project['Name'] . " to " . $stack[count($stack) - 1]['Name'] . " for a total of "
. count($stack[count($stack) - 1]['Children']) . " kids\n";
echo "\n";
} else {
echo "No parent\n";
}
echo "stack count: " . count($stack) . "\n";
$stack[] = &$project;
}
echo "Left in stack: " . count($stack) . "\n";
return $stack[0];
}
请注意,在三个地方添加了&符号。
由于这个问题,在php中使用嵌套数组和赋值运算符时必须非常小心。
这也意味着在嵌套数组中使用大量数据时,处理器使用率和内存占用量很大。 例如,在上面的例子中,当projectListToTree()返回时,完整的数组树被复制到局部变量$ tree并且(因为php垃圾收集器很糟糕)在内存中两次。
你有一个echo语句,看看你何时调用array_pop()? 通过阅读本文而不进行测试,我认为你正在从堆栈中弹出记录并扔掉它。
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