PHP/MongoDB: update a value in an array

Question

I have the following mongodb object:

{
 "_id": ObjectId("4d0b9c7a8b012fe287547157"),
 "messages": {
 "0": {
 "toUname": "Eamorr3",
 "fromUname": "Eamorr2",
 "time": 1292606586,
 "id": "ABCDZZZ",
 "subject": "asdf",
 "message": "asdf",
 "read": 0 //I want to change this to 1!
 },
 "1": {
 "toUname": "Eamorr1",
 "fromUname": "Eamorr3",
 "time": 1292606586,
 "id": "EFGHZZZ",
 "subject": "asdf2",
 "message": "asdf2",
 "read": 0
 }
 },
 "uname": "Eamorr3"
}

How do I set "read" to 1 where id=ABCDZZZZ? I'm using PHP.

I've tried the following command:

$driverInboxes->update(array('uname'=>$uname),array('$set'=>array('messages'=>array('id'=>$id,'read'=>'1'))));

But when I do this, overwriting occurs and I get:

{
 "_id": ObjectId("4d0b9c7a8b012fe287547157"),
 "messages": {
 "id": "j7zwr2hzx14d3sucmvp5",
 "read": "1"
 },
 "uname": "Eamorr3"
}

I'm totally stuck. Any help much appreciated.

Do I need to pull the entire array element, modify and and push it back in again?

Many thanks in advance,

• user956584: possible duplicate of MongoDB update nested array
• user956584: Actually right now its possible: stackoverflow.com/questions/11261521/…

Answer 1

If you read your command, you're actually saying: "UPDATE WHERE uname = Eamorr3 SET messages equal to this array (id=blah,read=1)"

When you do a $set on messages, you're basically instructing it to take your array as the new value.

However, it looks like you're trying to update a specific message as read which is just a little more complex. So there are two hurdles here:

1: You're actually updating messages.0.read

If you do array('$set' => array( 'messages.0.read' => 1 ) ), you will update the correct element. Follow that chain, messages is a javascript object and you want to update the property 0. The property 0 is itself a javascript object which contains the property read which you want to update.

Can you see how you're updating messages.0.read?

This brings us to problem #2.

2: the 0 is a problem for you

If you look at the way you've structured the data in Mongo, the messages object is really sub-par. The "0" and "1" are currently acting as "ids" and they're not very useful. Personally, I would structure your objects with the actual IDs in place of "0" or "1".

So your objects would look like the following:

{
 "_id": ObjectId("4d0b9c7a8b012fe287547157"),
 "messages": {
 "ABCDZZZ": {
 "toUname": "Eamorr3",
 "fromUname": "Eamorr2",
 "time": 1292606586,
 "subject": "asdf",
 "message": "asdf",
 "read": 0 //I want to change this to 1!
 }
 },
 "uname": "Eamorr3"
}

Now you're update command becomes this:

array('$set' => array( 'messages.ABCDZZZ.read' => 1 ) )

This structure makes it much easier to update a specific message or a specific portion of a message.

• Eamorr: Hey, I was thinking of restructuring like the way you mentioned. I think this is probably the best way to go. Otherwise, I'm going to have to look through the entire array, find the object index, and update.
• webjay: Also take a look at $elemMatch

Answer 2

If you want to keep the array structure for various purposes, you can use the Positional operator. This enables you to take advantage of array features ($pop,$push,etc) while simultaneously being able to update elements which are in an unknown array position.