Примеры выборок из БД в MODX и кол-во запросов к БД в зависимости от конструкции и способа запроса.

exampleQueries

Все примеры расположены в порядке уменьшения нагрузки на БД и при равенстве кол-ва запросов в порядке уменьшения кол-ва строк кода. Сверху самый ресурсоёмкий по кол-ву запросов к БД.
///////////////////////////////////////////////////////////
Пустая страница MODX при отключенном кэше:
кол-во зпросов/время запросов/время выполнения PHP кода/общее время
6/0.0002 s/0.0336 s/0.0338 s
***********************************************************
1-ый код с pdoFetch, все методы:

$pdo = $modx->getService('pdoFetch');
$pdo->setConfig(array(
	'class' => 'modResource',
	'where' => 'modResource.id = 200',
	'select' => 'id,pagetitle'
));
$res = $pdo->run();
print_r($res);

Вывод:
Array
(
    [id] => 200
    [pagetitle] => test 196
    [idx] => 1
    [link] => 
)
Кол-во запросов и время:
9 699 328: Memory usage
11/0.0008 s/0.0334 s/0.0342 s
***********************************************************
2-ой код без pdoFetch, без $o->_lazy = array() с getObject:

$q = $modx->newQuery('modResource');
$q->select('modResource.id,modResource.pagetitle');
$q->where(array(
    'id' => 200
));
if($o = $modx->getObject('modResource', $q)){
    //$o->_lazy = array();
    print_r($o->toArray());    
}

Вывод:
Array ( [id] => 200 [type] => document [contentType] => text/html [pagetitle] => test 196 [longtitle] => [description] => [alias] => test-196 [link_attributes] => [published] => 1 [pub_date] => 0 [unpub_date] => 0 [parent] => 0 [isfolder] => [introtext] => [content] => [richtext] => 1 [template] => 1 [menuindex] => 199 [searchable] => 1 [cacheable] => 1 [createdby] => 1 [createdon] => 2015-05-14 15:48:23 [editedby] => 0 [editedon] => 0 [deleted] => [deletedon] => 0 [deletedby] => 0 [publishedon] => 2015-05-14 15:48:23 [publishedby] => 1 [menutitle] => [donthit] => [privateweb] => [privatemgr] => [content_dispo] => 0 [hidemenu] => [class_key] => modDocument [context_key] => web [content_type] => 1 [uri] => [uri_override] => 0 [hide_children_in_tree] => 0 [show_in_tree] => 1 [properties] => )
Кол-во запросов и время:
10/0.0005 s/0.0336 s/0.0341 s
***********************************************************
3-ий код с pdoFetch, getCollection:

$pdo = $modx->getService('pdoFetch');
$res = $pdo->getCollection('modResource', '', array('class' => 'modResource',
	'where' => 'modResource.id = 200',
	'select' => 'id,pagetitle'));
print_r($res);

Вывод:
Array ( [0] => Array ( [id] => 200 [pagetitle] => test 196 ) )
Кол-во запросов и время:
9 699 328: Memory usage
10/0.0004 s/0.0321 s/0.0325 s
***********************************************************
4-ый код с pdoFetch, getArray:

$pdo = $modx->getService('pdoFetch');
$res = $pdo->getArray('modResource', '', array('class' => 'modResource',
	'where' => 'modResource.id = 200',
	'select' => 'id,pagetitle'));
print_r($res);

Вывод:
Array ( [id] => 200 [pagetitle] => test 196 )
Кол-во запросов и время:
9 699 328: Memory usage
10/0.0013 s/0.0339 s/0.0352 s
***********************************************************
5-ый код без pdoFetch, getObject и $o->_lazy = array():

$q = $modx->newQuery('modResource');
$q->select('modResource.id,modResource.pagetitle');
$q->where(array(
    'id' => 200
));
if($o = $modx->getObject('modResource', $q)){
    $o->_lazy = array();
    print_r($o->toArray());    
}

Вывод:
Array ( [id] => 200 [type] => document [contentType] => text/html [pagetitle] => test 196 [longtitle] => [description] => [alias] => [link_attributes] => [published] => [pub_date] => 0 [unpub_date] => 0 [parent] => 0 [isfolder] => [introtext] => [content] => [richtext] => 1 [template] => 0 [menuindex] => 0 [searchable] => 1 [cacheable] => 1 [createdby] => 0 [createdon] => 0 [editedby] => 0 [editedon] => 0 [deleted] => [deletedon] => 0 [deletedby] => 0 [publishedon] => 0 [publishedby] => 0 [menutitle] => [donthit] => [privateweb] => [privatemgr] => [content_dispo] => 0 [hidemenu] => [class_key] => modDocument [context_key] => web [content_type] => 1 [uri] => [uri_override] => 0 [hide_children_in_tree] => 0 [show_in_tree] => 1 [properties] => )
Кол-во запросов и время:
9/0.0005 s/0.0316 s/0.0321 s
***********************************************************
6-ой код с pdoFetch, избранными методами без pdoFetch::Run():

$pdo = $modx->getService('pdoFetch');
$pdo->setConfig(array(
	'class' => 'modResource',
	'where' => 'modResource.id = 200',
	'select' => 'id,pagetitle'
));
$pdo->makeQuery();
$pdo->addSelects();
$pdo->addWhere();
$query = $pdo->prepareQuery();
$query->execute();
$res = $query->fetch(PDO::FETCH_ASSOC);
print_r($res);

Вывод:
Array ( [id] => 200 [pagetitle] => test 196 )
Кол-во запросов и время:
9 699 328: Memory usage
8/0.0004 s/0.0340 s/0.0344 s
***********************************************************
7-ой код без pdoFetch, prepare и execute:

$q = $modx->newQuery('modResource');
$q->select('modResource.id,modResource.pagetitle');
$q->where(array(
    'id' => 200
));
$q->prepare();
$q->stmt->execute();
$result = $q->stmt->fetch(PDO::FETCH_ASSOC);
print_r($result);

Вывод:
Array ( [id] => 200 [pagetitle] => test 196 )
Кол-во запросов и время:
8/0.0007 s/0.0331 s/0.0338 s
***********************************************************
8-ой код, чистый PDO с SQL запросом непосредственно в скрипте:

$q = 'SELECT `modResource`.`id`, `modResource`.`pagetitle` FROM `modx_site_content` AS `modResource` WHERE `modResource`.`id` = 200';
$o = $modx->prepare($q);
$o->execute();
$res = $o->fetch(PDO::FETCH_ASSOC);
print_r($res);

Вывод:
Array ( [id] => 200 [pagetitle] => test 196 )
Кол-во запросов и время:
8/0.0005 s/0.0295 s/0.0300 s
///////////////////////////////////////////////////////////
Вывод: желательно использовать последние три способа выборки. Последний всё же не рекомендуется, но вполне возможно на "скорую руку".

Для изучения:
1. http://community.modx-cms.ru/blog/modx-xpdo/9693.html
2. https://bezumkin.ru/training/course2/3006/
3. https://modx.pro/help/5268/#comment-37676
4. http://habrahabr.ru/post/152123/