MongoDb return only one element from the array

Question

So my collection looks like this:

{
  "_id" : ObjectId("52722429d874590c15000029"),
  "name" : "Bags",
  "products" : [{
      "_id" : ObjectId("527225b5d87459b802000029"),
      "name" : "Prada",
      "description" : "Prada Bag",
      "points" : "234",
      "validDate" : 1382562000,
      "link" : "dasdad",
      "code" : "423423424",
      "image" : null
    }, {
      "_id" : ObjectId("5272307ad87459401a00002a"),
      "name" : "Gucci",
      "description" : "Gucii bag",
      "points" : "2342",
      "validDate" : 1383170400,
      "link" : "dsadada",
      "code" : "2342",
      "image" : null
    }]
}

and I want to get only the product with the _id 527225b5d87459b802000029, I tried this:

$this->find(array(
                '_id' => new \MongoId('52722429d874590c15000029'),
                'products._id' => new \MongoId('527225b5d87459b802000029')
                ));

But it returns the entire array for that collection, and I only want one...can this be done in mongo?

possible duplicate of MongoDB extract only the selected item in array — JohnnyHK
– JohnnyHK, Commented Oct 31, 2013 at 12:39
You need to add a projection parameter to your find or findOne call. — JohnnyHK
– JohnnyHK, Commented Oct 31, 2013 at 12:44
I found the solution using aggregate aggregate(array( array('$match' => array('_id' => '52722429d874590c15000029')), array('$unwind' => '$products'), array('$match' => array('products._id' => '5272307ad87459401a00002a')), )); — user2885793
– user2885793, Commented Oct 31, 2013 at 12:49

Yann Moisan · Accepted Answer · 2013-10-31 13:19:14Z

1

As mentioned in comments, you have to add a projection, and more precisely an $elemMatch. No need to use the aggregation framework in that case.

Example :

find( { _id: 1, "products._id": 4 }, { products: { $elemMatch: { _id: 4 } } } ).pretty()

answered Oct 31, 2013 at 13:19

Yann Moisan

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