Add Included callback (#894)

* ADD included callback

* Fix styling

* wip

docs/features/including-relationships.md

@@ -150,6 +150,23 @@ $posts = QueryBuilder::for(Post::class)
 // every post in $posts will contain a `comments_sum_votes` property
 ```
 
+## Callback includes
+
+If you want to define a tiny custom include, you can use a callback include. Using `AllowedInclude::callback(string $name, Closure $callback, ?string $internalName = null)` you can specify a Closure that will be executed when the includes is requested. 
+
+You can modify the `Builder` object to add your own query constraints.
+
+For example:
+
+```php
+QueryBuilder::for(User::class)
+    ->allowedIncludes([
+        AllowedInclude::callback('latest_post', function (Builder $query) {
+            $query->latestOfMany();
+        }),
+    ]);
+```
+
 ## Selecting included fields
 
 You can select only some fields to be included using the [`allowedFields` method on the query builder](https://spatie.be/docs/laravel-query-builder/v5/features/selecting-fields/).

src/AllowedInclude.php

@@ -2,8 +2,10 @@
 
 namespace Spatie\QueryBuilder;
 
+use Closure;
 use Illuminate\Support\Collection;
 use Illuminate\Support\Str;
+use Spatie\QueryBuilder\Includes\IncludedCallback;
 use Spatie\QueryBuilder\Includes\IncludedCount;
 use Spatie\QueryBuilder\Includes\IncludedExists;
 use Spatie\QueryBuilder\Includes\IncludedRelationship;
@@ -73,6 +75,13 @@ public static function exists(string $name, ?string $internalName = null): Colle
         ]);
     }
 
+    public static function callback(string $name, Closure $callback, ?string $internalName = null): Collection
+    {
+        return collect([
+            new static($name, new IncludedCallback($callback), $internalName),
+        ]);
+    }
+
     public static function custom(string $name, IncludeInterface $includeClass, ?string $internalName = null): Collection
     {
         return collect([

src/Includes/IncludedCallback.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace Spatie\QueryBuilder\Includes;
+
+use Closure;
+use Illuminate\Database\Eloquent\Builder;
+
+class IncludedCallback implements IncludeInterface
+{
+    protected Closure $callback;
+
+    public function __construct(Closure $callback)
+    {
+        $this->callback = $callback;
+    }
+
+    public function __invoke(Builder $query, string $relation)
+    {
+        $query->with([
+            $relation => $this->callback,
+        ]);
+    }
+}

tests/IncludeTest.php

@@ -14,6 +14,7 @@
 use Spatie\QueryBuilder\Includes\IncludeInterface;
 use Spatie\QueryBuilder\QueryBuilder;
 use Spatie\QueryBuilder\Tests\TestClasses\Models\MorphModel;
+use Spatie\QueryBuilder\Tests\TestClasses\Models\RelatedModel;
 use Spatie\QueryBuilder\Tests\TestClasses\Models\TestModel;
 
 beforeEach(function () {
@@ -69,6 +70,22 @@
     assertRelationLoaded($models, 'relatedModels');
 });
 
+it('can include an includes callback', function () {
+    $models = createQueryFromIncludeRequest('relatedModels')
+        ->allowedIncludes([
+            AllowedInclude::callback('relatedModels', fn ($query) => $query->whereKey(RelatedModel::first())),
+        ])
+        ->get();
+
+    assertRelationLoaded($models, 'relatedModels');
+
+    $models = $models->reverse();
+    expect($models->pop()->relatedModels)->toHaveCount(1);
+    expect($models)->each(
+        fn ($model) => $model->relatedModels->toHaveCount(0)
+    );
+});
+
 it('can include an includes count', function () {
     $model = createQueryFromIncludeRequest('relatedModelsCount')
         ->allowedIncludes('relatedModelsCount')