Add tests for updating existing pivot + add option for passing model

src/Illuminate/Database/Eloquent/Relations/Concerns/InteractsWithPivotTable.php

@@ -188,7 +188,7 @@ public function updateExistingPivot($id, array $attributes, $touch = true)
             $attributes = $this->addTimestampsToAttachment($attributes, true);
         }
 
-        $updated = $this->newPivotStatementForId($id)->update(
+        $updated = $this->newPivotStatementForId($this->parseId($id))->update(
             $this->castAttributes($attributes)
         );
 
@@ -488,6 +488,21 @@ protected function parseIds($value)
         return (array) $value;
     }
 
+    /**
+     * Get the ID from the given mixed value.
+     *
+     * @param  mixed  $value
+     * @return mixed
+     */
+    protected function parseId($value)
+    {
+        if ($value instanceof Model) {
+            return $value->getKey();
+        }
+
+        return $value;
+    }
+
     /**
      * Cast the given keys to integers if they are numeric and string otherwise.
      *

tests/Integration/Database/EloquentBelongsToManyTest.php

@@ -584,6 +584,44 @@ public function can_touch_related_models()
 
         $this->assertNotEquals('2017-10-10 10:10:10', Tag::find(300)->updated_at);
     }
+
+    /**
+     * @test
+     */
+    public function can_update_existing_pivot()
+    {
+        $tag = Tag::create(['name' => str_random()]);
+        $post = Post::create(['title' => str_random()]);
+
+        DB::table('posts_tags')->insert([
+            ['post_id' => $post->id, 'tag_id' => $tag->id, 'flag' => 'empty'],
+        ]);
+
+        $post->tagsWithExtraPivot()->updateExistingPivot($tag->id, ['flag' => 'exclude']);
+
+        foreach ($post->tagsWithExtraPivot as $tag) {
+            $this->assertEquals('exclude', $tag->pivot->flag);
+        }
+    }
+
+    /**
+     * @test
+     */
+    public function can_update_existing_pivot_using_model()
+    {
+        $tag = Tag::create(['name' => str_random()]);
+        $post = Post::create(['title' => str_random()]);
+
+        DB::table('posts_tags')->insert([
+            ['post_id' => $post->id, 'tag_id' => $tag->id, 'flag' => 'empty'],
+        ]);
+
+        $post->tagsWithExtraPivot()->updateExistingPivot($tag, ['flag' => 'exclude']);
+
+        foreach ($post->tagsWithExtraPivot as $tag) {
+            $this->assertEquals('exclude', $tag->pivot->flag);
+        }
+    }
 }
 
 class Post extends Model
@@ -601,6 +639,12 @@ public function tags()
             ->wherePivot('flag', '<>', 'exclude');
     }
 
+    public function tagsWithExtraPivot()
+    {
+        return $this->belongsToMany(Tag::class, 'posts_tags', 'post_id', 'tag_id')
+            ->withPivot('flag');
+    }
+
     public function touchingTags()
     {
         return $this->belongsToMany(TouchingTag::class, 'posts_tags', 'post_id', 'tag_id')