Make it possible to run the aggregation pipeline

src/Query/Builder.php

@@ -88,7 +88,7 @@ class Builder extends BaseBuilder
     /**
      * The database collection.
      *
-     * @var \MongoDB\Collection
+     * @var \MongoDB\Laravel\Collection
      */
     protected $collection;
 
@@ -569,7 +569,7 @@ public function generateCacheKey()
     public function aggregate($function = null, $columns = [])
     {
         if ($function === null) {
-            return new PipelineBuilder($this->getPipeline());
+            return new PipelineBuilder($this->getPipeline(), $this->collection, $this->options);
         }
 
         $this->aggregate = [

src/Query/PipelineBuilder.php

@@ -4,12 +4,33 @@
 
 namespace MongoDB\Laravel\Query;
 
+use MongoDB\Builder\BuilderEncoder;
 use MongoDB\Builder\Stage\FluentFactory;
+use MongoDB\Laravel\Collection;
 
-class PipelineBuilder extends FluentFactory
+use function array_replace;
+use function collect;
+
+final class PipelineBuilder extends FluentFactory
 {
-    public function __construct(array $pipeline = [])
-    {
+    public function __construct(
+        array $pipeline,
+        private Collection $collection,
+        private array $options,
+    ) {
         $this->pipeline = $pipeline;
     }
+
+    public function get()
+    {
+        $encoder = new BuilderEncoder();
+        $pipeline = $encoder->encode($this->getPipeline());
+
+        $options = array_replace(
+            ['typeMap' => ['root' => 'array', 'document' => 'array']],
+            $this->options,
+        );
+
+        return collect($this->collection->aggregate($pipeline, $options)->toArray());
+    }
 }

tests/Query/PipelineBuilderTest.php

@@ -4,8 +4,15 @@
 
 namespace MongoDB\Laravel\Tests\Query;
 
+use DateTimeImmutable;
+use Illuminate\Support\Collection;
 use MongoDB\BSON\Document;
+use MongoDB\BSON\ObjectId;
+use MongoDB\BSON\UTCDateTime;
 use MongoDB\Builder\BuilderEncoder;
+use MongoDB\Builder\Expression;
+use MongoDB\Builder\Type\TimeUnit;
+use MongoDB\Builder\Variable;
 use MongoDB\Laravel\Query\PipelineBuilder;
 use MongoDB\Laravel\Tests\Models\User;
 use MongoDB\Laravel\Tests\TestCase;
@@ -14,27 +21,71 @@
 
 class PipelineBuilderTest extends TestCase
 {
+    public function tearDown(): void
+    {
+        User::truncate();
+    }
+
     public function testCreateFromQueryBuilder(): void
     {
-        $builder = User::where('foo', 'bar')->aggregate();
-        assert($builder instanceof PipelineBuilder);
-        $builder->addFields(baz: 'qux');
+        User::insert([
+            // @todo apply cast to mass insert?
+            ['name' => 'John Doe', 'birthday' => new UTCDateTime(new DateTimeImmutable('1989-01-01'))],
+            ['name' => 'Jane Doe', 'birthday' => new UTCDateTime(new DateTimeImmutable('1990-01-01'))],
+        ]);
 
+        // Create the aggregation pipeline from the query builder
+        $pipeline = User::where('name', 'John Doe')->aggregate();
+        assert($pipeline instanceof PipelineBuilder);
+        $pipeline
+            ->addFields(
+                age: Expression::dateDiff(
+                    startDate: Expression::dateFieldPath('birthday'),
+                    endDate: Variable::now(),
+                    unit: TimeUnit::Year,
+                ),
+            )
+            ->unset('birthday');
+
+        // The encoder is used to convert the pipeline to a BSON document
         $codec = new BuilderEncoder();
-        $pipeline = $codec->encode($builder->getPipeline());
-        $json = Document::fromPHP(['pipeline' => $pipeline])->toCanonicalExtendedJSON();
+        $json = Document::fromPHP([
+            'pipeline' => $codec->encode($pipeline->getPipeline()),
+        ])->toCanonicalExtendedJSON();
 
+        // Compare with the expected pipeline
         $expected = Document::fromPHP([
             'pipeline' => [
                 [
-                    '$match' => ['foo' => 'bar'],
+                    '$match' => ['name' => 'John Doe'],
                 ],
                 [
-                    '$addFields' => ['baz' => 'qux'],
+                    '$addFields' => [
+                        'age' => [
+                            '$dateDiff' => [
+                                'startDate' => '$birthday',
+                                'endDate' => '$$NOW',
+                                'unit' => 'year',
+                            ],
+                        ],
+                    ],
+                ],
+                [
+                    '$unset' => ['birthday'],
                 ],
             ],
         ])->toCanonicalExtendedJSON();
 
         $this->assertJsonStringEqualsJsonString($expected, $json);
+
+        // Execute the pipeline and verify the results
+        $results = $pipeline->get();
+
+        $this->assertInstanceOf(Collection::class, $results);
+        $this->assertCount(1, $results);
+        $this->assertInstanceOf(ObjectId::class, $results->first()['_id']);
+        $this->assertSame('John Doe', $results->first()['name']);
+        $this->assertIsInt($results->first()['age']);
+        $this->assertArrayNotHasKey('birthday', $results->first());
     }
 }