Fix isset for relationships

lib/Model.php

@@ -360,7 +360,27 @@ public function &__get($name)
      */
     public function __isset($attribute_name)
     {
-        return array_key_exists($attribute_name, $this->attributes) || array_key_exists($attribute_name, static::$alias_attribute);
+        // check for aliased attribute
+        if (array_key_exists($attribute_name, static::$alias_attribute)) {
+            return true;
+        }
+
+        // check for attribute
+        if (array_key_exists($attribute_name, $this->attributes)) {
+            return true;
+        }
+
+        // check for getters
+        if (method_exists($this, "get_${attribute_name}")) {
+            return true;
+        }
+
+        // check for relationships
+        if (static::table()->has_relationship($attribute_name)) {
+            return true;
+        }
+
+        return false;
     }
 
     /**

test/ActiveRecordTest.php

@@ -298,6 +298,9 @@ public function test_isset()
         $book = new Book();
         $this->assert_true(isset($book->name));
         $this->assert_false(isset($book->sharks));
+
+        $author = Author::find(1);
+        $this->assert_true(isset($author->awesome_person));
     }
 
     public function test_readonly_only_halt_on_write_method()

test/RelationshipTest.php

@@ -589,7 +589,6 @@ public function test_eager_loading_has_many_array_of_includes()
 
         foreach ($assocs as $assoc) {
             $this->assert_internal_type('array', $authors[1]->$assoc);
-            $this->assert_true(empty($authors[1]->$assoc));
         }
 
         $this->assert_sql_has('WHERE author_id IN(?,?)', ActiveRecord\Table::load('Author')->last_sql);