mongo php find $in issue with _id's - php

Question

I'm fairly new to Mongo and PHP. I've been fine with the relatively simple stuff but I've hit a snag performing a php find within a mongo collection conditionally limited by an array of _id's.
Here's a walkthrough...
// "characters" collection
{ "_id":{"$id":"3f177b70df1e69fe5c000001"}, "firstname":"Bugs", "lastname":"Bunny" }
{ "_id":{"$id":"3f2872eb43ca8d4704000002"}, "firstname":"Elmer", "lastname":"Fudd" }
{ "_id":{"$id":"3f287bb543ca8de106000003"}, "firstname":"Daffy", "lastname":"Duck" }
// "items" collection
{ "_id":{"$id":"4f177b70df1e69fe5c000001"}, "mdl":"carrot", "mfg":"Wild Hare Farms ltd.", "ownerid":{"$id":"3f177b70df1e69fe5c000001"} }
{ "_id":{"$id":"4f2872eb43ca8d4704000002"}, "mdl":"hat", "mfg":"Acme Inc.", "ownerid":{"$id":"3f2872eb43ca8d4704000002"} }
{ "_id":{"$id":"4f287bb543ca8de106000003"}, "mdl":"spaceship", "mfg":"Acme Inc.", "ownerid":{"$id":"3f287bb543ca8de106000003"} }
// Let's say I do a find on the item collection for a specific manufacturer...
$itemOwners = $db->items->find(array("mfg" => "Acme Inc."), array("ownerid"));
// The result looks something like this...
[
"4f2872eb43ca8d4704000002":{"_id":{"$id":"4f2872eb43ca8d4704000002"},"ownerid":{"$id":"3f2872eb43ca8d4704000002"}},
"4f287bb543ca8de106000003":{"_id":{"$id":"4f287bb543ca8de106000003"},"ownerid":{"$id":"3f287bb543ca8de106000003"}}
]
// I'd now like to perform a find on the character collection and get the corresponding owner documents.
// To do that I need to build the $in array from the previous find results...
foreach ($itemOwners as $doc)
$itemOwnersTemp[] = $doc["ownerid"];
$itemOwners = $itemOwnersTemp;
// The resulting array looks like this. I've read that the ids need to be in MongoId format. Seems like they are?
[
{"$id":"3f2872eb43ca8d4704000002"},
{"$id":"3f287bb543ca8de106000003"}
]
// and (finally) the conditional find. The result set is always empty. What am I tripping up on?
$characterDocs = $db->characters->find(array("_id" => array('$in' => $itemOwners));

Answer 1

I've just tried this with slightly modified code:
<?php
$m = new Mongo('localhost:13000', array( 'replicaSet' => 'a' ) );
$db = $m->demo;
$db->authenticate('derick', 'xxx');
// "characters" collection
$c = $db->characters;
$c->insert(array( '_id' => new MongoID("3f177b70df1e69fe5c000001"), 'firstname' => 'Bugs', 'lastname' => 'Bunny' ));
$c->insert(array( '_id' => new MongoID("3f2872eb43ca8d4704000002"), 'firstname' => 'Elmer', 'lastname' => 'Fudd' ));
$c->insert(array( '_id' => new MongoID("3f287bb543ca8de106000003"), 'firstname' => 'Daffy', 'lastname' => 'Duck' ));
// "items" collection
$c = $db->items;
$c->insert(array( '_id' => new MongoId("4f177b70df1e69fe5c000001"), 'mdl' => 'carrot', 'ownerid' => new MongoID('3f177b70df1e69fe5c000001')));
$c->insert(array( '_id' => new MongoId("4f2872eb43ca8d4704000002"), 'mdl' => 'hat', 'ownerid' => new MongoID('3f2872eb43ca8d4704000002')));
$c->insert(array( '_id' => new MongoId("4f287bb543ca8de106000003"), 'mdl' => 'space', 'ownerid' => new MongoID('3f287bb543ca8de106000003')));
// Let's say I do a find on the item collection for a specific manufacturer...
$itemOwners = $db->items->find(array("mdl" => "hat"), array("ownerid"));
// The result looks something like this...
/*[
"4f2872eb43ca8d4704000002":{"_id":{"$id":"4f2872eb43ca8d4704000002"},"ownerid":{"$id":"3f2872eb43ca8d4704000002"}},
"4f287bb543ca8de106000003":{"_id":{"$id":"4f287bb543ca8de106000003"},"ownerid":{"$id":"3f287bb543ca8de106000003"}}
]*/
// I'd now like to perform a find on the character collection and get the corresponding owner documents.
// To do that I need to build the $in array from the previous find results...
foreach ($itemOwners as $doc) {
$itemOwnersTemp[] = $doc["ownerid"];
}
$itemOwners = $itemOwnersTemp;
// The resulting array looks like this. I've read that the ids need to be in MongoId format. Seems like they are?
/*
[
{"$id":"3f2872eb43ca8d4704000002"},
{"$id":"3f287bb543ca8de106000003"}
]
*/
// and (finally) the conditional find. The result set is always empty. What am I tripping up on?
$characterDocs = $db->characters->find(array("_id" => array('$in' => $itemOwners)));
var_dump( iterator_to_array( $characterDocs ) );
?>
And it provides the output that I expect:
array(1) {
["3f2872eb43ca8d4704000002"]=>
array(3) {
["_id"]=>
object(MongoId)#3 (1) {
["$id"]=>
string(24) "3f2872eb43ca8d4704000002"
}
["firstname"]=>
string(5) "Elmer"
["lastname"]=>
string(4) "Fudd"
}
}
Somewhere, I think you're doing a wrong conversion but it's difficult to tell as you don't show the output of PHP.

Answer 2

Instead of this:
$itemOwnersTemp[] = $doc["ownerid"];
Try this:
$itemOwnersTemp[] = new MongoID($doc["ownerid"]);