Foreign keys

[qurben]

Make the framework understand foreign keys.

[qurben]

Notation idea:

Given this class

class Car extends PersistentEntity {
	public $id;
	public $num_wheels;
	public $brand;

        protected $brand_id;

	protected static $persistent_attributes = [
		'id' => array(T::Integer, false, 'auto_increment'),
		'num_wheels' => array(T::Integer),
		'brand_id' => array(T::Timestamp),
	];
	protected static $table_name = 'CiviSaldo';
	protected static $primary_key = ['id'];
}

Define foreign keys as follows:

protected static $foreign_keys = [['brand_id' => CarBrand::class, 'brand']];

I don't know how straightforward reading this would be, but it would be variable containing key -> class referenced, where the reference is stored.
or

protected static $foreign_keys = [['fk' => 'brand_id', 'ref' => CarBrand::class, 'in' => 'brand']];

Same as previous.

Or just

protected static $foreign_keys = [['brand' => CarBrand::class]];

Where a hidden foreign key field is created in the database.

[qurben]

The magic functions __get and __set can be used to only retrieve the referenced objects when needed.

It would also be nice to be able to set a flag to join a referenced object on database level, thus limiting the amount of database queries.

[qurben]

Other way around should also be possible

$relations = [
  'children' => Child::class
];

[brussee]

If you are going to embark in this: make sure you can model many-to-many relationships nicely.
Example: any person can be a parent and a child; 1 parent can have multiple children; 1 child can have multiple parents.

[qurben]

My idea for this would be using a through model, which must be explicitely defined. This keeps behaviour transparent because no invisible tables have to be created. The way Django does it.

$relations = [
  'children' = [Child::class, ChildParentThrough::class] 
];

Something like that. Where the through has to fk's an can contain arbritrary data.