Fix collections attachments. (#889)

* Fix collections attachments.

If you will try to attach model simultaneously to a collection of related models, you'll crash your app, because this method will try to operate with models themselves but not with their ids.

This change considers every case and fixes collections relations.

* Fix typo

src/Jenssegers/Mongodb/Relations/BelongsToMany.php

@@ -179,6 +179,10 @@ class BelongsToMany extends EloquentBelongsToMany
             // Attach the new parent id to the related model.
             $model->push($this->foreignKey, $this->parent->getKey(), true);
         } else {
+            if ($id instanceof Collection) {
+                $id = $id->modelKeys();
+            }
+
             $query = $this->newRelatedQuery();
 
             $query->whereIn($this->related->getKeyName(), (array) $id);

tests/RelationsTest.php

@@ -291,6 +291,18 @@ class RelationsTest extends TestCase
         $this->assertCount(2, $user->clients);
     }
 
+    public function testBelongsToManyAttachEloquentCollection()
+    {
+        $user = User::create(['name' => 'John Doe']);
+        $client1 = Client::create(['name' => 'Test 1']);
+        $client2 = Client::create(['name' => 'Test 2']);
+        $collection = new \Illuminate\Database\Eloquent\Collection([$client1, $client2]);
+
+        $user = User::where('name', '=', 'John Doe')->first();
+        $user->clients()->attach($collection);
+        $this->assertCount(2, $user->clients);
+    }
+
     public function testBelongsToManySyncAlreadyPresent()
     {
         $user = User::create(['name' => 'John Doe']);