Flat Laravel collection to tree - laravel

Question

I have a Laravel collection of pages - each page has a "parent_id" property. It resembles this.
"pages": [
{
"id": 1,
"title": "Page 1 Level 1",
"parent_id": 0
},
{
"id": 2,
"title": "Page 2 Level 2",
"parent_id": 1
},
{
"id": 3,
"title": "Page 3 Level 3",
"parent_id": 2
},
{
"id": 4,
"title": "Page 4 Level 1",
"parent_id": 0
},
{
"id": 5,
"title": "Page 5 Level 2",
"parent_id": 4
},
{
"id": 6,
"title": "Page 6 Level 3",
"parent_id": 5
},
{
"id": 7,
"title": "Page 7 Level 1",
"parent_id": 0
},
{
"id": 8,
"title": "Page 8 Level 2",
"parent_id": 7
}
]
What I am trying to do is format the output so they are nested with the correct hierarchy. So for example:
"pages": [
{
"id": 1,
"title": "Page 1 Level 1",
"parent_id": 0,
"children": [
{
"id": 2,
"title": "Page 2 Level 2",
"parent_id": 1,
"children": [
{
"id": 3,
"title": "Page 3 Level 3",
"parent_id": 2,
"children": []
}
]
},
]
},
{
"id": 4,
"title": "Page 4 Level 1",
"parent_id": 0,
"children": [
{
"id": 5,
"title": "Page 5 Level 2",
"parent_id": 4,
"children": [
{
"id": 6,
"title": "Page 6 Level 3",
"parent_id": 5,
"children": []
}
]
},
]
},
{
"id": 7,
"title": "Page 7 Level 1",
"parent_id": 0,
"children": [
{
"id": 8,
"title": "Page 8 Level 2",
"parent_id": 7,
"children": []
},
]
},
]
The hierarchy can be any number of levels deep. I have a nearly working version as shown below, but it does contain a bug. Whilst the various child objects are nesting with their parent, they also remain at the root level. So it looks like duplicates are actually placed in their nested positions.
Can anyone help me finish this off?
PageController
$pages = Page::with('children')->get();
Page
public function directChildren(): HasMany
{
return $this->hasMany($this, 'parent_id', 'id');
}
public function children(): HasMany
{
return $this->directChildren()->with('children'));
}

Answer 1

You could try something like this to nest these records:
$c = collect($data)->keyBy('id');
$result = $c->map(function ($item) use ($c) {
if (! ($parent = $c->get($item->parent_id))) {
return $item;
}
$parent->children[] = $item;
})->filter();

Answer 2

All your parent elements seem to have 0 as parent_id. If this is the case, the following query should work:
$pages = Page::where('parent_id', 0)->with('children')->get();
You are basically selecting all parent pages first, then attaching its children tree. Without the where, you are selecting all pages, and attaching their children.
The other option is to define a parent relationship in the model, and select parents with children using something like whereDoesntHave('parent'..)->with(children)

Answer 3

Building on #lagbox's answer:
/**
* Build a tree from a flat list of Pages.
*
* #param Collection|Page[] $pages
* #return Collection|Page[]
*/
public static function asTree(Collection $pages)
{
$pages = $pages->keyBy('id');
return $pages->map(function (Page $page) use ($pages) {
if (is_null($page->parent_id)) {
// or $page->parent_id === 0 if using 0 to indicate top-level pages
return $page;
}
/** #var Page $parent */
$parent = $pages->get($page->parent_id);
// manually set the relation to avoid re-querying the database
if (!$parent->relationLoaded('children')) {
$parent->setRelation('children', collect()->push($page));
} else {
$parent->children->push($page);
}
return null;
})
->filter()
->values();
}
I've also simplified the relationships to just a single hasMany referring to direct descendants only.
// Page.php
/**
* #return \Illuminate\Database\Eloquent\Relations\HasMany
*/
public function children()
{
return $this->hasMany(Page::class, 'parent_id', 'id');
}