alter person model

Nested_Models.md

@@ -58,3 +58,37 @@ UPDATE people SET home_id = 2 WHERE id = 4;
 ```
 
 The previous code will find the row with an `id` of 4 and set the `home_id` column to 2.
+
+## Update the Person model
+
+First, let's add the functionality to allow the `Person` class to have an optional `home_id`:
+
+```php
+class Person {
+    public $id;
+    public $name;
+    public $age;
+    public function __construct($id, $name, $age, $home_id = null) {
+        $this->id = $id;
+        $this->name = $name;
+        $this->age = $age;
+        if($home_id){
+            $this->home_id = $home_id;
+        }
+    }
+}
+```
+
+Now we can create a Person like we did before without a home id:
+
+```php
+$new_person = new Person(1, "Bob", 23);
+```
+
+Or with it:
+
+```php
+$new_person = new Person(1, "Bob", 23, 7);
+```
+
+If no 4th parameter is specified in `new Person`, `$home_id` in the constructor will be `null`, and the `if` statement will not run.  If it is specified, then the `if` statement will run and set `$this->home_id`.