<?php
$a = $modx->getCollection('modResource', 3);
$b = $modx->getCollection('modResource', 3);

$obj = $a[3];
print ($a[3] === $obj ? 1: 0); // result 1

$obj = $b[3];
print ($a[3] === $obj ? 1: 0); // result 0

<?php
print '<pre>';
$a = array(
    2 => 'object'    
);

$b = array(
    2 => 'new object',
    5 => 'object',
    7 => 'object',
) + $a;

print_r($b);

Array
(
    [2] => new object
    [5] => object
    [7] => object
)

<h1>Доступные номера</h1>

<p style="padding-top:10px; font-weight:bold;"> Выберите понравившийся номер и необходимые дополнительные услуги </p>

{processor ns=Hotel action="web/reservation/step/search/index" assign=result nocache}

{if $result.success==true}
    <table cellspacing="0" cellpadding="0" border="0" id="room-types-cont" class="base-cont">
        <thead><tr>
                <td class="cell left-holder"> </td>
                <td class="cell name">Категория номера</td>
                <td colspan="2" class="cell price"> Цена за
<strong>1 ночь</strong>, 
                    <span class="currency">руб.</span></td>
                <td class="cell quantity">Количество номеров</td>
                <td class="cell amount right-cell">Стоимость, <span class="currency">руб.</span></td></tr>
        </thead>
        <tbody>
            
            
            {* All rooms *}
            {foreach from=$result.object key=room_id item=room nocache}
                {* counf variables *}
                {assign var=variables_total value=count($room.variables)}
                <tr>
                    <td class="cell left-holder" rowspan="{$variables_total+2}"> </td>
                    <td class="cell" rowspan="{$variables_total+2}">
                        <div class="title">{$room.room.title}</div>
                    </td>
                    <td class="cell empty-cell"> </td>
                    <td class="cell empty-cell"> </td>
                    <td class="cell empty-cell"> </td>
                    <td class="cell empty-cell"> </td>
                </tr>
                
                {* All variables *}
                {foreach from=$room.variables key=variable_id item=variable}
                    <tr>
                        <td class="cell empty-cell"> </td>
                        <td class="cell empty-cell"> </td>
                        <td class="cell empty-cell"> </td>
                        <td class="cell empty-cell"> </td>
                    </tr>
                {/foreach}
                {* Eof All variables *}
                
                <tr class="room-type">
                    <td class="cell persons empty-cell border-top-0"> </td>
                    <td class="cell price empty-cell border-top-0"> </td>
                    <td class="cell quantity empty-cell border-top-0"> </td>
                    <td class="cell amount empty-cell border-top-0"> </td>
                </tr>
                
            {/foreach}
            {* Eof All rooms *}
        </tbody>
    </table>
{else}
    {$result.message}
{/if}

{if $result.success==true}

{else}
    {$result.message}
{/if}

{foreach from=$result.object key=room_id item=room nocache}

<td class="cell left-holder" rowspan="{$variables_total+2}">

{foreach from=$room.variables key=variable_id item=variable}

[[+var:notempty=`[[!mysnippet]]`]]

{if $var!=''}
    {snippet name=mysnippet}
{/if}

<?php
print '<pre>';
$a = array(
    2=>'object'    
);

$b = $a + array(
    2 => 'new object',
    5 =>'object',
    7 => 'object',
);

print_r($b);

Array
(
    [2] => object
    [5] => object
    [7] => object
)

Нет, так нельзя делать. Это ссумируем массивы, а нам надо заменять уже имеющиеся.

$a = array("a" => "apple", "b" => "banana");
$b = array("a" => "pear", "b" => "strawberry", "c" => "cherry");
$c = $b + $a;
var_dump($c);

// array(3) {
//   ["a"]=>
//   string(4) "pear"
//   ["b"]=>
//   string(10) "strawberry"
//   ["c"]=>
//   string(6) "cherry"
// }

(
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `item` int(10) unsigned NOT NULL,
  `datefrom` datetime NOT NULL,
  `datetill` datetime NOT NULL,
  PRIMARY KEY (`id`),
  KEY `item` (`item`,`datefrom`,`datetill`)
)

<?php
print '<pre>';

$datefrom = "2013-04-06 12:00:01";
$datetill = "2013-04-08 11:59:59";

$c = $modx->newQuery('HotelRoomItem');
$c->leftJoin('HotelRoomReserve', 'Reserves', "Reserves.item=HotelRoomItem.id 
    AND (
        (Reserves.datefrom between '{$datefrom}' AND '{$datetill}')
        OR (Reserves.datetill between '{$datefrom}' AND '{$datetill}')
        OR (Reserves.datefrom < '{$datefrom}' AND Reserves.datetill > '{$datetill}')
    )"
);

$c->select(array(
    'HotelRoomItem.id as item_id',
    'Reserves.*',
));

$where = array(
    'HotelRoomItem.active' => 1,
    'Reserves.id' => null,
);

$c->where($where);

SELECT 
	HotelRoomItem.id as item_id, 
	Reserves.* 
FROM 
	`modx_hotel_room_items` AS `HotelRoomItem` 
	LEFT JOIN `modx_hotel_room_reserve` `Reserves` ON Reserves.item=HotelRoomItem.id      
		AND (         
			(Reserves.datefrom between '2013-04-06 12:00:01' AND '2013-04-08 11:59:59')         
			OR (Reserves.datetill between '2013-04-06 12:00:01' AND '2013-04-08 11:59:59')         
			OR (Reserves.datefrom < '2013-04-06 12:00:01' AND Reserves.datetill > '2013-04-08 11:59:59')     
		) 
WHERE  ( `HotelRoomItem`.`active` = 1 AND `Reserves`.`id` IS NULL )

$this->_relatedObjects[$alias]= $collection + $this->_relatedObjects[$alias];

а если не ошибаюсь, то нужен коммит, чтобы в 2.2.7 зарелизить успели

$this->_relatedObjects[$alias]= $collection + $this->_relatedObjects[$alias];