TreeModel

Use Cases

A TreeModel, or nested subset, is especially usefull for storing and retreiving the complete tree of subsequent models. It will prevent many queries while building the layout, like:

• level 1 - A
  • level 2 - AA
    • level 3 - AAA
    • level 3 - AAB
      • level 4 - AABA
      • ...
  • level 2 - AB
  • ...
• ...

Examples for use is a menu for pages or categories.

It could also be used to count all underlying related models, for example all products in a category and underlying categories:

$allCategories = $category->allChildren()->select(id);

$productCount = Product::whereHas('categories', function ($query) use ($allCategories, $category) {
    $query->whereIn('id', $allCategories);
    $query->orWhere('id', '=', $category->id);
})->count();

(note: this is just pseudocode, propably not working)

Using TreeModel

This package has 2 core-functionalities: the migration-helper and a relation to be included inside an Eloquent Model. The migration-helper will be included using the TreeModelServiceProvider, however, the relation will also work without it.

Install

Require this package with composer.

composer require simpeldigitaal/tree-model

If you don't use auto-discovery, add the ServiceProvider to the providers array in config/app.php

SimpelDigitaal\TreeModel\TreeModelServiceProvider::class

Use

Inside your migration:

up

    public function up()
    {
        Schema::table('menu', function (Blueprint $table) {
            ...
            $table->tree();
            ...
        });
    
    
        Schema::table('categories', function (Blueprint $table) {
            ...
            $table->treeWithId();
            ...
        });
    }

$table->tree($prefix = 'tree'); Generates the necessary fields for storing the tree (tree_start and tree_end). You are able to change the default prefix.

$table->treeWithId($name = 'parent_id', $prefix = 'tree'); Generates besides the necessary fields for storing the tree the parent-child relation too. This field may be used in a HasMany or BelongsTo relation.

and down

    public function down()
    {
        Schema::table('menu', function (Blueprint $table) {
            ...
            $table->dropTree();
            ...
        });
            
        Schema::table('categories', function (Blueprint $table) {
            ...
            $table->dropTreeWithId();
            ...
        });

    }    

$table->dropTree($prefix = 'tree'); Drops the fields for the tree.

$table->dropTreeWithId($name = 'parent_id', $prefix = 'tree'); Drops the field for the parent-child relation too...

Inside your model:

Include the SimpelDigitaal\WebTree\Concerns\HasTree-trait to your Eloquent-Model.

On top:

use SimpelDigitaal\WebTree\Concerns\HasTree;

Inside your model:

class Categories extends Model {

    use HasTree
    ...
    public function allChildren()
    {
        return $this->getTree();
    }

    public function childrenFromTree()
    {
        return $this->getSubsetTree('allChildren');
    }
    ...
}

getTree will fetch all children from the database. childrenFromTree will fetch the subset for the next level, seeding all children with their own subset. It will use and it will set the relation specified as first parameter.

Building the tree.

After storing a new model or changing an existing model, you have to build the tree again using $model->buildsTree();

Building layout:

Example:

    $categories = Category::whereNull('parent_id')->with('allChildren')->get();

<ul>
    @foreach($categories as $category)
        <li>
            {{ $category->name }} | {{ $category->treeStart }} - {{ $category->treeEnd }}
            @include('categories._list', ['categories' => $category->childrenFromTree()])
        </li>
    @endforeach
</ul>

Builds with only two queries: first to retreive $categories, second for eagerloading relation 'allChildren'

Enjoy

Tips

Adding constraints

If you want to add a constraint to your tree (for example a site_id), you are able to set this constraint using a global scope.

Sources

• Inspired by the 'nested set' of the Joomla-framework
  • Especially this article, from Gijs Van Tulder
  • Wikipedia about this 'Tree'