Added belongs to level via relation (#13)

* add belongs to level via relation

src/Relations/BelongsToLevel.php

@@ -0,0 +1,62 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Umbrellio\LTree\Relations;
+
+use Illuminate\Database\Eloquent\Builder;
+use Illuminate\Database\Eloquent\Collection;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\Concerns\SupportsDefaultModels;
+use Illuminate\Database\Eloquent\Relations\Relation;
+
+class BelongsToLevel extends Relation
+{
+    use SupportsDefaultModels;
+
+    protected $level;
+
+    protected $relationName;
+
+    public function __construct(Builder $query, Model $parent, int $level, $relationName)
+    {
+        $this->level = $level;
+        $this->relationName = $relationName;
+
+        parent::__construct($query, $parent);
+    }
+
+    public function addConstraints()
+    {
+        $this->query->ancestorByLevel($this->level);
+    }
+
+    public function addEagerConstraints(array $models)
+    {
+        $this->query->ancestorByLevel($this->level);
+    }
+
+    public function initRelation(array $models, $relation)
+    {
+        foreach ($models as $model) {
+            $model->setRelation($relation, $this->getDefaultFor($model));
+        }
+
+        return $models;
+    }
+
+    public function match(array $models, Collection $results, $relation)
+    {
+        return $models;
+    }
+
+    public function getResults()
+    {
+        return $this->query->first();
+    }
+
+    protected function newRelatedInstanceFor(Model $parent)
+    {
+        return $this->related->newInstance();
+    }
+}

src/Traits/HasTreeRelationships.php

@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Umbrellio\LTree\Traits;
+
+use Illuminate\Database\Eloquent\Concerns\HasRelationships;
+use Illuminate\Database\Eloquent\Model;
+use Umbrellio\LTree\Relations\BelongsToLevel;
+
+/**
+ * @mixin HasRelationships
+ * @mixin LTreeModelTrait
+ * @mixin Model
+ */
+trait HasTreeRelationships
+{
+    protected function belongsToLevel($related, int $level = 1, ?Model $instance = null, ?string $relation = null)
+    {
+        if ($relation === null) {
+            $relation = $this->guessBelongsToRelation();
+        }
+
+        $instance = $instance ?: $this->newRelatedInstance($related);
+
+        return new BelongsToLevel($instance->newQuery(), $this, $level, $relation);
+    }
+}

src/Traits/LTreeModelTrait.php

@@ -112,10 +112,15 @@ public function renderAsLtree($value, $pad_string = LTreeHelper::PAD_STRING, $pa
 
     public function getAncestorByLevel(int $level = 1)
     {
-        return static::whereRaw(sprintf(
-                "({$this->getLtreePathColumn()} @> text2ltree('%s')) and  nlevel(path) = %d",
+        return static::scopeAncestorByLevel($level)->first();
+    }
+
+    public function scopeAncestorByLevel(Builder $query, int $level = 1): Builder
+    {
+        return $query->whereRaw(sprintf(
+                "({$this->getLtreePathColumn()} @> text2ltree('%s')) and nlevel(path) = %d",
                 LTreeHelper::pathAsString($this->getLtreePath()),
                 $level)
-        )->first();
+        );
     }
 }