# Advanced usage

## Custom data source adapters

At some point you may run across a data type that is not covered by the packaged adapters. In this
case, you will need to write your own.

To do so, you must implement `Zend\Paginator\Adapter\AdapterInterface`. There are two methods
required to do this:

- `count()`
- `getItems($offset, $itemCountPerPage)`

Additionally, you'll want to implement a constructor that takes your data source as a parameter and
stores it as a protected or private property. How you wish to go about doing this specifically is up
to you.

If you've ever used the SPL interface
[Countable](http://www.php.net/~helly/php/ext/spl/interfaceCountable.html), you're familiar with
`count()`. As used with zend-paginator, this is the total number of items in the data collection.
Additionally, the `Zend\Paginator\Paginator` instance provides a method `countAllItems()` that
proxies to the adapter `count()` method.

The `getItems()` method is only slightly more complicated. For this, your adapter is supplied with
an offset and the number of items to display per page. You must return the appropriate slice of
data. For an array, that would be:

```php
return array_slice($this->_array, $offset, $itemCountPerPage);
```

Take a look at the packaged adapters (all of which implement the
`Zend\Paginator\Adapter\AdapterInterface`) for ideas of how you might go about implementing your
own.

## Custom scrolling styles

Creating your own scrolling style requires that you implement
`Zend\Paginator\ScrollingStyle\ScrollingStyleInterface`, which defines a single method,
`getPages()`. Specifically,

```php
public function getPages(Zend\Paginator\Paginator $paginator, $pageRange = null);
```

This method should calculate a lower and upper bound for page numbers within the range of so-called
"local" pages (that is, pages that are nearby the current page).

Unless it extends another scrolling style (see `Zend\Paginator\ScrollingStyle\Elastic` for an
example), your custom scrolling style will inevitably end with something similar to the following
line of code:

```php
return $paginator->getPagesInRange($lowerBound, $upperBound);
```

There's nothing special about this call; it's merely a convenience method to check the validity of
the lower and upper bound and return an array of the range to the paginator.

When you're ready to use your new scrolling style, you'll need to tell `Zend\Paginator\Paginator`
what directory to look in. To do that, do the following:

```php
$manager = Zend\Paginator\Paginator::getScrollingStyleManager();
$manager->setInvokableClass('my-style', 'My\Paginator\ScrollingStyle');
```

## Caching features

`Zend\Paginator\Paginator` can be told to cache the data it has already passed on, preventing the
adapter from fetching them each time they are used. To tell paginator to automatically cache the
adapter's data, just pass to its `setCache()` method a pre-configured cache object implementing the
`Zend\Cache\Storage\StorageInterface` interface.

```php
$cache = StorageFactory::adapterFactory('filesystem', array(
    'cache_dir' => '/tmp',
    'ttl'       => 3600,
    'plugins'   => array( 'serializer' ),
));
Zend\Paginator\Paginator::setCache($cache);
```

As long as `Zend\Paginator\Paginator` has been seeded with a cache storage object the data it
generates will be cached. Sometimes you would like not to cache data even if you already passed a
cache instance. You should then use `setCacheEnable()` for that.

```php
// $cache is a Zend\Cache\Storage\StorageInterface instance
Zend\Paginator\Paginator::setCache($cache);
// ... later on the script
$paginator->setCacheEnable(false);
// cache is now disabled
```

When a cache is set, data are automatically stored in it and pulled out from it. It then can be
useful to empty the cache manually. You can get this done by calling
`clearPageItemCache($pageNumber)`. If you don't pass any parameter, the whole cache will be empty.
You can optionally pass a parameter representing the page number to empty in the cache:

```php
// $cache is a Zend\Cache\Storage\StorageInterface instance
Zend\Paginator\Paginator::setCache($cache);
// $paginator is a fully configured Zend\Paginator\Paginator instance
$items = $paginator->getCurrentItems();
// page 1 is now in cache
$page3Items = $paginator->getItemsByPage(3);
// page 3 is now in cache

// clear the cache of the results for page 3
$paginator->clearPageItemCache(3);

// clear all the cache data
$paginator->clearPageItemCache();
```

Changing the item count per page will empty the whole cache as it would have become invalid:

```php
// $cache is a Zend\Cache\Storage\StorageInterface instance
Zend\Paginator\Paginator::setCache($cache);
// fetch some items
// $paginator is a fully configured Zend\Paginator\Paginator instance
$items = $paginator->getCurrentItems();

// all the cache data will be flushed:
$paginator->setItemCountPerPage(2);
```

It is also possible to see the data in cache and ask for them directly. `getPageItemCache()` can be
used for that:

```php
// $cache is a Zend\Cache\Storage\StorageInterface instance
Zend\Paginator\Paginator::setCache($cache);
// $paginator is a fully configured Zend\Paginator\Paginator instance
$paginator->setItemCountPerPage(3);
// fetch some items
$items = $paginator->getCurrentItems();
$otherItems = $paginator->getItemsPerPage(4);

// see the cached items as a two-dimension array:
var_dump($paginator->getPageItemCache());
```