php-notes/Nested_Models.md

Nesting Models

Objectives

Currently, we only have two unrelated models: people and locations. Let's add the functionality so that whenever we have JSON that represents a person, it will contain a home property, which is the associated location object:

{
    "id":4,
    "name":"Bob",
    "age":25,
    "home": {
        "id":2,
        "street": "123 Fake Street",
        "city": "Aurora",
        "state": "NY"
    }
}

Also, when we have a location, it will contain an array of people objects:

{
    "id":2,
    "street": "123 Fake Street",
    "city": "Aurora",
    "state": "NY",
    "inhabitants":[
        {
            "id":4,
            "name":"Bob",
            "age":25
        },        
        {
            "id":7,
            "name":"Sally",
            "age":74
        },        
    ]
}

This will be a one-to-many relationship

Add home_id to people

First, go into psql and add a home_id INT column to the people table:

ALTER TABLE people ADD COLUMN home_id INT;

Now we can give people homes like so:

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:

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:

$new_person = new Person(1, "Bob", 23);

Or with it:

$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.