Added magic __isset check for presenter to work for objects properties (#59)

Author: matthewnw

src/Presenter.php

@@ -139,6 +139,25 @@ public function __get($attribute)
         return $this->model->{$attribute};
     }
 
+    /**
+     * Dynamically check a property exists on the underlying object.
+     *
+     * @param  mixed  $attribute
+     * @return bool
+     */
+    public function __isset($attribute)
+    {
+        $method = $this->getStudlyAttributeMethod($attribute);
+
+        if (method_exists($this, $method)) {
+            $value = $this->{$method}($this->model);
+
+            return ! is_null($value);
+        }
+
+        return isset($this->model->{$attribute});
+    }
+
     /**
      * Convert the Presenter to a string.
      *

tests/PresenterTest.php

@@ -449,4 +449,44 @@ public function output_keys_cannot_be_unset_via_array_access()
 
         unset($presenter['email']);
     }
+
+    /** @test */
+    public function can_check_isset_on_presenter_for_model_attribute()
+    {
+        $presenter = factory(User::class)
+            ->create(['name' => 'David Hemphill'])
+            ->present(UserProfilePresenter::class);
+
+        $this->assertTrue(isset($presenter->name));
+    }
+
+    /** @test */
+    public function can_check_isset_on_presenter_for_accessor()
+    {
+        $user = factory(User::class)->create();
+        $presenter = new class($user) extends Presenter
+        {
+            public function getSayHelloAttribute()
+            {
+                return 'Hello from the Presenter!';
+            }
+        };
+
+        $this->assertTrue(isset($presenter->say_hello));
+    }
+
+    /** @test */
+    public function can_check_isset_is_false_on_presenter_for_accessor_if_returns_null()
+    {
+        $user = factory(User::class)->create();
+        $presenter = new class($user) extends Presenter
+        {
+            public function getSayHelloAttribute()
+            {
+                return null;
+            }
+        };
+
+        $this->assertFalse(isset($presenter->say_hello));
+    }
 }