Bitrix Framework

Base collection class implements the \Iterator interface, allowing to get items:

$books = \Bitrix\Main\Test\Typography\BookTable::getList()
	->fetchCollection();

foreach ($books as $book)
{
	// ...
}

Collection items can also be fetched directly. The method getAll returns all the contained objects as an array:

$books = \Bitrix\Main\Test\Typography\BookTable::getList()
	->fetchCollection();

$bookObjects = $books->getAll();

echo $bookObjects[0]->getId();
// prints ID value for the first object

The method getByPrimary gets specific objects, contained in the collection:

// 1. example with standard primary key
$books = \Bitrix\Main\Test\Typography\BookTable::getList()
		->fetchCollection();
	
$book = $books->getByPrimary(1);
// book with ID=1

// 2. example with composite primary key
$booksToAuthor = \Bitrix\Main\Test\Typography\BookAuthorTable::getList()
	->fetchCollection();

$bookToAuthor = $booksToAuthor->getByPrimary(
	['BOOK_ID' => 2, 'AUTHOR_ID' => 18]
);
// assigns relations for book object with ID=2 and author with ID=18

You can check availability of specific object in the collection using the method has:

$book1 = \Bitrix\Main\Test\Typography\Book::wakeUp(1);
$book2 = \Bitrix\Main\Test\Typography\Book::wakeUp(2);

$books = \Bitrix\Main\Test\Typography\BookTable::query()
	->addSelect('*')
	->whereIn('ID', [2, 3, 4])
	->fetchCollection();

var_dump($books->has($book1));
// prints false

var_dump($books->has($book2));
// prints true

Similarly, the method hasByPrimary is convenient for checking by the primary key:

$books = \Bitrix\Main\Test\Typography\BookTable::query()
	->addSelect('*')
	->whereIn('ID', [2, 3, 4])
	->fetchCollection();

var_dump($books->hasByPrimary(1));
// prints false

var_dump($books->hasByPrimary(2));
// prints true

Objects are added by the method add and interface ArrayAccess, allowing to use the structure []:

$book1 = \Bitrix\Main\Test\Typography\Book::wakeUp(1);

$books = \Bitrix\Main\Test\Typography\BookTable::query()
	->addSelect('*')
	->whereIn('ID', [2, 3, 4])
	->fetchCollection();

$books->add($book1);
// or
$books[] = $book1;

You can delete object from collection either directly or by specifying the primary key:

$book1 = \Bitrix\Main\Test\Typography\Book::wakeUp(1);

$books = \Bitrix\Main\Test\Typography\BookTable::getList()
	->fetchCollection();

$books->remove($book1);
// book with ID=1 is deleted from collection

$books->removeByPrimary(2);
// book with ID=2 is deleted from collection