Can't access values in MongoDB with cursor using PHP

Question

I seem to be having some trouble using the cursor as I try to pull data out of a MongoDB. Here is a screenshot of my simple data structure:

data structure screenshot http://droplr.com/IpcH+

I'm trying to use the following:

$collection_name = "users";
$collection = $this->mongo->db->$collection_name;
$which_document = array("email" => $email_address);
$which_fields = array("words");
$cursor = $collection->find($which_document, $which_fields);

But my $cursor does not seem to be going any further into the document than the actual document. In the end, I'm looking to sort() and limit() on the created_at field within the "words" field, but I seem to be at an impasse here. And either MongoDB's error passing isn't very helpful, or I've no idea how to use it properly. (I'd assume the latter.)

One idea: I'm not sure the "words" table being generated inside of square brackets is correct, but here is the code I'm using to insert data here:

function create_word($word, $email_address){
    $collection = 'users';

// make sure word isn't null
if($word !== NULL){

// add new data to the 'words' set
    $new_data = array('$addToSet' => array('words' => array(
                                                            'word' => $word,
                                                            'status' => 'open',
                                                            'created_at' => time()
                                                            )));
    $this->mongo->db->$collection->update(array('email' => $email_address), $new_data);         
}

Thanks so much for any help you can give!

halfdan · Accepted Answer · 2010-09-22 21:43:16Z

2

You can't sort subdocuments. You need to do it on the client side. In your case retrieve the words array:

$array = iterator_to_array($cursor); 
$words = $array[0]["words"];

and then use php to sort the values.

edited Sep 22, 2010 at 21:43

answered Sep 22, 2010 at 20:39

halfdan

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3 Comments

Joshua Cody Over a year ago

Ah, dot notation! Is there a hard-and-fast rule on when one should use dot notation in the php driver? Unfortunately, no luck. Here is a screenshot of a var_dump of the cursor value using this code. Did I miss something from your updates? I'm actually going to be sorting on created_at, but I tried to alternate between "1" and "-1", with no differences.

halfdan Over a year ago

I was curious and tried it myself now. Sorting subdocuments doesn't work. The example in the documentation covers a different kind of sorting where you have nested values inside a document and sort all the documents after them and not an nested array.

Joshua Cody Over a year ago

Interesting. This is my first project with MongoDB, from your vantage point, would you suggest some sort of data restructuring? This seems like a fairly important issue, as I'll be essentially paginating this data, it would be very nice to use .limit(), .skip(), and .sort().

sdot257 · Accepted Answer · 2010-09-22 21:32:39Z

1

Try

$collection->find(array($which_document, $which_fields))->sort(array("words.created_at" => -1));

answered Sep 22, 2010 at 21:32

sdot257

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5 Comments

Joshua Cody Over a year ago

Unfortunately I have no luck here. Whether I use 1 or -1, my var_dump remains the same.

sdot257 Over a year ago

Let's clarify shall we? You're trying to sort the "words" array by the "created_at?" I'm not sure if you can do that. I raised this issue w/ the developers. See the following discussion I raised on mongodb's forum groups.google.com/group/mongodb-user/browse_thread/thread/…

Joshua Cody Over a year ago

Sounds like you and halfdan are both pointing to the same issue. Reading through the thread now, but I'll pose the same question here as I have with him. Would you suggest a data restructuring since I'll be working so intensively with this data?

sdot257 Over a year ago

If the "words" array will get large, I would separate it into its own collection.

Joshua Cody Over a year ago

Thanks so much, the intangibles of best data structure practices and minor things that won't work are difficult to grasp at first. Looks like I need to break myself of the idea that as much as possible should be stored in a single collection.

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