Question

We have some embedded documents that look like this:

 {
"_id" : ObjectId("4e402353bc9f6ec5a6000001"),
"first_name" : "Chris",
"last_name" : "Jones",

    "alerts" : [
    {
        "_id" : ObjectId("4f7cd6ffc067db00070022d4"),
        "name" : "Default",
        "email_frequency" : "weekly",
        "interested_industries" : [
            "Computer Software",
            "Internet"
        ],
        "interested_employers" : [
            "Facebook",
            "AOL"
        ],
        "interested_skills" : [ ],
        "matches" : [
            ObjectId("4ee46a2a0dd0c70017000365"),
            ObjectId("4efa1707bacfa40001012b65"),
            ObjectId("4e402376bc9f6ec5a6000a7a"),
            ObjectId("4e4e0eb8d052fc4028021f66"),
            ObjectId("4ee55d8500ca410014000003"),
            ObjectId("4ee63d06d96b850001008688"),
            ObjectId("4e57be7ed052fc606a002335"),
            ObjectId("4f05d47d9ce340001702ba42"),
            ObjectId("4f200ffcaf5f34000e0021a4"),
            ObjectId("4e4de701d052fc33da00052f")
        ],
        "updated_at" : ISODate("2012-05-03T18:26:14.774Z")
    }
]
 }

Since the document above is contained in an array, I’m having trouble picking it out form the selector with something like this:

User.collection.update({"_id" => user.id}, {:$set => {"alert.matches" => matches}})

But this will update all #alerts matches. I just want to update the one alert with the ID “4fa7fd60e5be08bcc9000644”.

Answer 1

You can probably use the positional operator to identify the array element:

The $ positional operator

The $ operator (by itself) means “position of the matched array item in the query”. Use this to find an array member and then manipulate it.

So perhaps something like:

User.collection.update(
    { :_id => user.id, :matches => BSON::ObjectId('4e40238dbc9f6ec5a6000eed') },
    { :$set => { 'alert.matches.$' => matches } }
)

But as Sergio notes, it is difficult to tease out the structure of your documents based on the limited information in your question.

---

Looks like more information came in after I answered and it looks like:

{ :$set => { 'alerts.$.matches' => ... } }

is what you need. And you will need to include :matches in the query so that $ has something to refer to.