feat: toggle strict null parent root nodes

README.md

@@ -63,6 +63,16 @@ SelectTree::make('categories')
     ->relationship(relationship: 'categories', titleAttribute: 'name', parentAttribute: 'parent_id', modifyChildQueryUsing: fn($query) => $query));
 ```
 
+Note: when you filter the parent query, any results found by the child query whose parents have been filtered out will be promoted to root nodes by default (to prevent empty result sets).
+To disable this feature, use the `strictNullParentRootNodes()` configuration method
+
+```php
+SelectTree::make('categories')
+    ->relationship(relationship: 'categories', titleAttribute: 'name', parentAttribute: 'parent_id', modifyQueryUsing: fn($query) => $query->where('id', 1))
+    ->strictNullParentRootNodes(); // only children of parent results from the parent query will be included in the tree
+```
+
+
 ## Methods
 
 Set a custom placeholder when no items are selected

src/SelectTree.php

@@ -72,6 +72,8 @@ class SelectTree extends Field implements HasAffixActions
 
     protected ?Closure $modifyChildQueryUsing = null;
 
+    protected Closure|bool $strictNullParentRootNodes = false;
+
     protected Closure|int $defaultOpenLevel = 0;
 
     protected string $direction = 'auto';
@@ -246,8 +248,11 @@ private function buildTreeFromResults($results, $parent = null): Collection
             }
         }
 
-        // Filter the cache for missing parents in the result set and get the children
-        $orphanedResults = array_map(
+        // If the tree has strict rull parent root nodes, only retrieve children whose parent is the null value
+        // Otherwise, promote other orphaned children to root nodes
+        $orphanedResults = $this->hasStrictNullParentRootNodes()
+        ? [$parent => $resultCache[$parent]['children']]
+        : array_map(
             fn ($item) => $item['children'],
             array_filter(
                 $resultCache,
@@ -256,6 +261,7 @@ private function buildTreeFromResults($results, $parent = null): Collection
         );
 
         // Move any remaining children from the cache into the root of the tree, since their parents do not show up in the result set
+
         $resultMap[$parent] = [];
         foreach ($orphanedResults as $orphanedResult) {
             $resultMap[$parent] += $orphanedResult;
@@ -333,6 +339,13 @@ public function query(Builder|Closure|null $query, string $titleAttribute, strin
         return $this;
     }
 
+    public function strictNullParentRootNodes(Closure|bool $condition = true): static
+    {
+        $this->strictNullParentRootNodes = $condition;
+
+        return $this;
+    }
+
     public function withCount(bool $withCount = true): static
     {
         $this->withCount = $withCount;
@@ -400,6 +413,11 @@ public function getQuery(): ?Builder
         return $this->getRelationship()->getRelated()->query();
     }
 
+    public function hasStrictNullParentRootNodes(): bool
+    {
+        return $this->evaluate($this->strictNullParentRootNodes);
+    }
+
     public function getTitleAttribute(): string
     {
         return $this->evaluate($this->titleAttribute);