问题
I am having trouble understanding the datamapper design pattern. I have two queries (one to get albums and one to get artist). I want to produce a list of albums and artists (band members). There is a one to many relationship between the two.
SQL Queries
public function getArtist()
{
$adapter = $this->getAdapter();
$sql = new Sql($adapter);
$select = $sql->select();
$select->from('genre');
$select->where(array(
'album_id' => $album,));
$selectString = $sql->getSqlStringForSqlObject($select);
$resultSet = $adapter->query($selectString, $adapter::QUERY_MODE_EXECUTE);
return $resultSet;
}
public function getAlbum()
{
$adapter = $this->getAdapter();
$sql = new Sql($adapter);
$select = $sql->select();
$select->from('album');
$selectString = $sql->getSqlStringForSqlObject($select);
$resultSet = $adapter->query($selectString, $adapter::QUERY_MODE_EXECUTE);
return $resultSet;
}
When I do something similar to below I end up running a separate query for each album. I don't want to do this. How do I go about setting something like this up http://akrabat.com/php/objects-in-the-model-layer-part-2/ ? Can I set up so each entity represents a query (I would like to use joins in my queries as opposed to creating an entity for each table)?
<?php foreach ($albums->getAlbum() as $album) : ?>
<tr>
<td><?php echo $this->escapeHtml($album->id);?></td>
<td><?php echo $this->escapeHtml($album->title);?></td>
<td><?php echo $this->escapeHtml($album->artist);?></td>
<td>
<?php foreach ($albums->getArtist($album->id) as $member) : ?>
Using Solution Provided Below
ConcreteAlbumMapper.php
use Zend\Db\Adapter\AdapterInterface;
use Album\Model\AlbumMapper;
namespace Album\Model;
class ConcreteAlbumMapper implements AlbumMapper {
public function __construct(AdapterInterface $dbAdapter)
{
$this->adapter =$dbAdapter;
}
public function fetchAlbums(ArtistMapper $artistMapper) {
$adapter = $this->getAdapter();
$sql = new Sql($adapter);
$select = $sql->select();
$select->from('album');
$selectString = $sql->getSqlStringForSqlObject($select);
$albumRows = $adapter->query($selectString, $adapter::QUERY_MODE_EXECUTE);
$albums = array();
foreach ($albumRows as $albumRow) {
$albums[$albumRow['id']] = new Album($albumRow);
}
$artists = $artistMapper->fetchByAlbumIds(array_keys($albums));
//marrying album and artists
foreach ($artists as $artist) {
/**
* not crazy about the getAlbumId() part, would be better to say
* $artist->attachYourselfToAnAlbumFromThisIndexedCollection($albums);
* but going with this for simplicity
*/
$albums[$artist->getAlbumId()]->addArtist($artist);
}
return $albums;
}
}
ConcreteMemberMapper.php
<?php
namespace Album\Model;
use Zend\Db\Adapter\AdapterInterface;
use Zend\Db\Sql\Sql;
use Album\Model\Member;
class ConcreteMemberMapper {
public function __construct(AdapterInterface $dbAdapter)
{
$this->adapter =$dbAdapter;
}
public function getAdapter()
{
if (!$this->adapter) {
$sm = $this->getServiceLocator();
$this->adapter = $sm->get('Zend\Db\Adapter\Adapter');
}
return $this->adapter;
}
public function fetchByAlbumIds($ids) {
$adapter = $this->getAdapter();
$sql = new Sql($adapter);
$select = $sql->select();
$select->from('members');
$select->where(array(
'album_id' => $ids));
$selectString = $sql->getSqlStringForSqlObject($select);
$results = $adapter->query($selectString, $adapter::QUERY_MODE_EXECUTE);
return $results;
//return \Zend\Stdlib\ArrayUtils::iteratorToArray($results);
}
public function getAlbumId()
{
return $this->albumId;
}
}
Album.php
<?php
namespace Album\Model;
use Zend\InputFilter\InputFilter;
use Zend\InputFilter\InputFilterAwareInterface;
use Zend\InputFilter\InputFilterInterface;
class Album //implements InputFilterAwareInterface
{
public $id;
public $title;
public $artist;
public $members = array();
public function __construct($data) {
$this->id = (!empty($data['id'])) ? $data['id'] : null;
$this->artist = (!empty($data['artist'])) ? $data['artist'] : null;
$this->title = (!empty($data['title'])) ? $data['title'] : null;
$this->members = (!empty($data['members'])) ? $data['members'] : null;
}
public function addMember(Member $member) {
$this->members[] = $member;
}
AlbumController.php
public function indexAction()
{
$dbAdapter = $this->getServiceLocator()->get('Zend\Db\Adapter\Adapter');
//$album = new Album();
$albumMapper = new ConcreteAlbumMapper($dbAdapter);
$memberMapper = new ConcreteMemberMapper($dbAdapter);
$bar=$albumMapper->fetchAlbums($memberMapper);
//$artistMapper = new
//var_dump($bar);
return new ViewModel(array(
'albums' => $bar,
));
}
Many Thanks
Matt
回答1:
There are many ways to approach this, this is one of them. Let's say you have a db schema similar to this:
Now you can have AlbumMapper and ArtistMapper responsible for fetching those objects from the db for you:
interface AlbumMapper {
/**
* Fetches the albums from the db based on criteria
* @param type $albumCriteria
* @param ArtistMapper $artistMapper
*
* Note: the ArtistMapper here can be also made optional depends on your app
*/
public function fetchBySomeCriteria($albumCriteria, ArtistMapper $artistMapper);
}
interface ArtistMapper {
/**
* @param array $ids
* @return Artist[]
*/
public function fetchByAlbumIds(array $ids);
}
I've put that AlbumMapper requires ArtistMapper so with this mapper Albums are always returned with their artists. Now an example implementation can be like this where I use a little indexing trick to attach artist to albums:
class ConcreteAlbumMapper implements AlbumMapper {
public function fetchBySomeCriteria($albumCriteria, ArtistMapper $artistMapper) {
//sql for fetching rows from album table based on album criteria
$albums = array();
foreach ($albumRows as $albumRow) {
$albums[$albumRow['id']] = new Album($albumRow);
}
$artists = $artistMapper->fetchByAlbumIds(array_keys($albums));
//marrying album and artists
foreach ($artists as $artist) {
/**
* not crazy about the getAlbumId() part, would be better to say
* $artist->attachYourselfToAnAlbumFromThisIndexedCollection($albums);
* but going with this for simplicity
*/
$albums[$artist->getAlbumId()]->addArtist($artist);
}
return $albums;
}
}
In this case your Album will be along the lines of:
class Album {
private $id;
private $title;
private $artists = array();
public function __construct($data) {
//initialize fields
}
public function addArtist(Artist $artist) {
$this->artists[] = $artist;
}
}
At the end of all this you should have a collection of Album objects initialized with their Artists.
来源：https://stackoverflow.com/questions/27277173/how-to-use-a-data-mapper-with-sql-queries