mongodb - Why can the documents referred to by a PHP MongoCursor object changes after a for each loop iterates through it? -

first explain situation, ask question.

situation:

assuming php mongodb database object "db" refers database has collection called "products". each document in our "products" collection looks this:

{    _id: <objectid>   upc_code: <int>   discontinued: <bool>   for_sale: <bool>   modified: <date> } 

imagine there thousands of these documents. imagine each, "discontinued" false, , "for_sale" true. modified dates not same.

step 1: search 100 oldest-modified products:

$newproducts = db->products->find(array('discontinued'=>false))->sort(array('modified'=>1))->limit(100); 

step 2: "for each" loop through $newproducts, , check each one's "upc_code" via api external web service. each product has been discontinued, update database, setting "discontinued" value true:

foreach($newproducts $product) {     $discontinued = checkapi($product['upc_code']);     if($discontinued) {         $update = array('$set'=>array('discontinued'=>true));         db->products->update->(array('_id'=>$product['_id']),$update);     } } 

step 3: after done, again iterate through $newproducts "for each" loop , make array of "_id" values:

$mongo_ids = array(); foreach($newproducts $product) {     $mongo_ids[] = $product['_id']; } 

step 4: update products "_id" values $in array, $set "modified" value current time:

$modified = myfunctiontogetcurrenttime(); $query = array('_id'=>array('$in'=>$mongo_ids)); $update2 = array('$set'=>array('modified'=>$modified));  $options = array('upsert'=>false,'multiple'=>true); db->products->update($query,$update2,$options); 

the problem none of products "discontinued" value got set true have "modified" property updated in step 4 because $products mongocursor object, , therefore in step 3 $products refers different set of documents in step 2, due fact in step 2, in of documents update value of same property mongocursor's query based on ("discontinued").

question:

therefore question is, firstly, why set of documents referred mongocursor object change this? there way "bake" it, documents found @ time of query don't change later? if there no way "bake" (so speak), best way store returned documents in variable not dynamic?

(note: know can $newproductsarray = iterator_to_array($newproducts) after step 1 store results of query in static variable. i'm more curious if there might way set mongocursor's options wouldn't necessary.)