MongoDB Aggregation: Value in Array

Question

We have the following Testsnippet in Ruby

def self.course_overview(course_member=nil)
  course_member = CourseMember.last if course_member == nil

  group_global = {"$group" =>
    {"_id" => { "course_id" => "$course_id",
                "title" => "$title",
                "place" => "$place",
                "description" => "$description",
                "choosen_id" => "$choosen_id",
                "year" => {"$year" => "$created_at"},
                "course_member_ids" => "$course_member_ids"}}
  }

  match_global = {"$match" => {"_id.course_member_ids" => {"$in" => "#{course_member.id}"} }}


  test = CoursePlan.collection.aggregate([group_global, match_global])

  return test
end

The problem is the "match_global" statement. We would like to match all Documents where the course_member ID is appearing in the course_member_ids array.

The above statement fails with the error: "...must be an array". This make sense to me but according to other comments on the web this should be possible this way.

Any advice? How is it possible to return the docs where the course_member id is in the array of the course_member ids?

Sample CoursePlan Object:

{
    "_id" : ObjectId("5371e70651a53ed5ad000055"),
    "course_id" : ObjectId("5371e2e051a53ed5ad000039"),
    "course_member_ids" : [ 
        ObjectId("5371e2a751a53ed5ad00002d"), 
        ObjectId("5371e2b251a53ed5ad000030"), 
        ObjectId("5371e2bb51a53ed5ad000033")
    ],
    "created_at" : ISODate("2014-05-13T09:33:58.042Z"),
    "current_user" : "51b473bf6986aee9c0000002",
    "description" : "Schulung 1 / Elektro",
    "fill_out" : ISODate("2014-04-30T22:00:00.000Z"),
    "place" : "TEST",
    "title" : "Schulung 1",
    "updated_at" : ISODate("2014-05-13T09:33:58.811Z"),
    "user_ids" : [ 
        ObjectId("51b473bf6986aee9c0000002"), 
        ObjectId("521d7f606986ae4826000002"), 
        ObjectId("521d8b3f6986aed678000007")
    ]
}

Not sure but I think you are looking for elemMatch. stackoverflow.com/questions/23469463/… — Lalit Agarwal
– Lalit Agarwal, Commented May 13, 2014 at 9:17
How can we use elemMatch on a "flat" array like ["123", "234"]? Because, i think, elemMatch needs a object like [{val: "123"}, {val: "234"}]. — patrickkeller
– patrickkeller, Commented May 13, 2014 at 9:25
Kind of a little hard given you have not presented any sample data. But the general premise is correct even though the array is "anonymous" for key values. So how about some relevant data? — Neil Lunn
– Neil Lunn, Commented May 13, 2014 at 9:29
what is the course_member_ids in the original documents? If it's an array of course member ids then just test for equality. {$match:{"_id.course_member_ids":<valueYouWantToTest>}} in shell terms. You don't need $in. — Asya Kamsky
– Asya Kamsky, Commented May 13, 2014 at 9:38

Asya Kamsky · Accepted Answer · 2014-05-13 15:03:28Z

1

Since course_member_ids is an array of course members you should test for equality. In shell syntax:

{$match:{"_id.course_member_ids":<valueYouWantToTest>}}

You don't need $in as this query is analogous to a find when you want to select documents that have a particular single value you are looking for.

answered May 13, 2014 at 15:03

Asya Kamsky

42.4k5 gold badges113 silver badges133 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

MongoDB Aggregation: Value in Array

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related