MongoDB filter array element in a nested object

Question

I have a document as follows:

{
    "_id" : ObjectId("56423b2558cb340599108b35"),
    "test" : {
        "source" : [
            {
                "member" : "abc"
            },
            {
                "member" : "xyz"
            }
        ]
    }
}

I want to filter on the array element xyz, and I am trying the following query:

db.coll.find({ "test.source.member" : "xyz" }, { "test.source.$.member" : true }).pretty()

Apparently it used to work on 2.4, on 2.6 it does not work,

On 2.4 it returned the "xyz", whereas on 2.6 it returns "abc" i.e. the first element. Is there a way to filter "abc" because eventually i want to update. BTW, i also tried with $elemMatch and it seems to give the same output "abc".

Thanks.

The posted 'code' is definitely not C, so please remove the 'c' tag — user3629249
– user3629249, Commented Nov 13, 2015 at 8:29

Abdullah Rasheed · Accepted Answer · 2015-11-10 21:53:56Z

5

According to the Docs, if you are running 2.6, this should give you the correct output:

db.coll.find({ "test.source.member" : "xyz"}, { "test.source.$" : 1}).pretty()

You could extract the member by doing this:

var member = db.coll.find(
                 { "test.source.member" : "xyz"},
                 { "test.source.$" : 1}
                 ).test.source[0].member;

The value of member would be:

xyz

edited Nov 10, 2015 at 21:53

answered Nov 10, 2015 at 19:40

Abdullah Rasheed

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8 Comments

user2766839 Over a year ago

Same as before. does not show the correctly filtered item.

Abdullah Rasheed Over a year ago

@user2766839 when you run db.version() what does it output in mongo shell?

Lisa Gagarina Over a year ago

@inspired, shouldn't it be { "test.source.$" : 1 } instead of { "test.source.$.member" : 1 } in order to get only the first element from the source array that has member "xyz"? If no, can you please explain why? Thanks.

user2766839 Over a year ago

I tried inserting a fresh query and then the filtering works. However after upgrade the filtering does not seem to work in other records. Currently investigating that.

Abdullah Rasheed Over a year ago

@LisaGagarina, you are right test.source.$ is correct, but when i tested test.source.$.member I didn't get an error. Thanks, I'll update it

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