Question

I am building a social network in mongo db.
Following is the structure of document in the groups collection. It represents each social group present in the system. Users are a part of this group which is represented by the ‘members’ property which is an array if json objects.

{
  "group_name":"my group",
  "members": [
    {
      "user_id": ObjectId("4e29341986ba75dc14000000"),
      "joined": ISODate("2011-07-26T11:46:49.0Z")
    },
    {
      "user_id": ObjectId("4e2ea94286ba75f81500000e"),
      "joined": ISODate("2011-07-26T11:47:55.0Z")
    },
    {
      "user_id": ObjectId("4e2eaa0786ba75e815000003"),
      "joined": ISODate("2011-07-26T11:55:22.0Z")
    },
    {
      "user_id": ObjectId("4e2eab7f86ba75ec1500000a"),
      "joined": ISODate("2011-07-26T11:57:44.0Z")
    },
    {
      "user_id": ObjectId("4e2eac3586ba75dc15000000"),
      "joined": ISODate("2011-07-26T12:00:57.0Z")
    },
    {
      "user_id": ObjectId("4e2eacae86ba75dc15000004"),
      "joined": ISODate("2011-07-26T12:02:43.0Z")
    },
    {
      "user_id": ObjectId("4e2eadbb86ba75ec1500000c"),
      "joined": ISODate("2011-07-26T12:07:01.0Z")
    }
  ]

The problem I am facing is how do I check if a user belongs to a certain group.
This is what I came up with but it doesn’t seem to work.
Please help.

    $criteria = array(
        '_id' => new MongoId($group_id),
        'members' => array('user_id' => new MongoId($user_id))
    );


   return $collection->find($criteria);

Answer 1

try with the following code:

$criteria = array(
        '_id' => new MongoId($group_id),
        'members.user_id' => new MongoId($user_id))
    );


return $collection->find($criteria);

see http://www.mongodb.org/display/DOCS/Dot+Notation+%28Reaching+into+Objects%29