MongoDB select where in array of _id?

Question

is possible in mongo db to select collection's documents like in SQL :

SELECT * FROM collection WHERE _id IN (1,2,3,4);

or if i have a _id array i must select one by one and then recompose the array/object of results?

score 213 · Accepted Answer · answered Oct 10 '11 at 13:26

213

Easy :)

db.collection.find( { _id : { $in : [1,2,3,4] } } );

taken from: http://www.mongodb.org/display/DOCS/Advanced+Queries#AdvancedQueries-%24in

answered Oct 10 '11 at 13:26

programmersbook

3,674
1
19
13

Do we still get benefits of indexing? IDs in that case are passed as plain strings... – Rafal Pastuszak Aug 21 '14 at 11:06
2

You do. However time complexity is linear (n), not logarithmic/constant. Without index it would be n^2. – Petr Brazdil Aug 22 '14 at 06:38
Is it not `O(log(n) * m)` where `n` is the size of the collection and `m` is the number of ids passed ? – Guig Nov 30 '16 at 00:50
15

U have to use ObjectId function, if "_id" is the ID object — {_id: {$in: [ObjectId("5a633609670aeb6f93b88b23")]}} – Pax Beach May 13 '18 at 12:26

score 10 · Answer 2 · answered Aug 12 '20 at 07:30

Because mongodb uses bson and for bson is important attribute types. and because _id is ObjectId you must use like this:

db.collection.find( { _id : { $in : [ObjectId('1'),ObjectId('2')] } } );

and in mongodb compass use like this:

{ "_id" : { $in : [ObjectId('1'),ObjectId('2')] } }

Note: objectId in string has 24 length.

score 5 · Answer 3 · answered Jan 21 '17 at 22:23

5

In this code list is the array of ids in user collection

var list = ["5883d387971bb840b7399130","5883d389971bb840b7399131","5883d38a971bb840b7399132"]

    .find({ _id: {$in : list}})

answered Jan 21 '17 at 22:23

KARTHIKEYAN.A

14,686
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4

The code is not working. It seems have to set IDs as ObjectId("5883d387971bb840b7399130") – Pax Beach May 15 '18 at 09:13
How do we do set them to ObjectIds programmatically? I tried the approach suggested by @klipmode in one of the answers, but that does not work. – Vikalp Jain May 06 '21 at 04:36

score 4 · Answer 4 · answered Dec 13 '20 at 11:38

4

You can try this

var ids = ["5883d387971bb840b7399130","5883d389971bb840b7399131","5883d38a971bb840b7399132"];

var oids = [];
ids.forEach(function(item){
oids.push(new ObjectId(item));
});

.find({ _id: {$in : oids}})

answered Dec 13 '20 at 11:38

klipmode

41
1

Thanks. Remember to define ObjectID like this: var ObjectId = require('mongodb').ObjectID; – Andrei Charnyshou Mar 23 '22 at 13:48

score 0 · Answer 5 · answered Nov 12 '20 at 10:25

if you want to find by user and also by another field like conditionally, you can easily do it like beneath with spread and ternary operator using aggregate and match

 const p_id = patient_id;
    let fetchingReports = await Reports.aggregate([
      ...(p_id
        ? [
            {
              $match: {
                createdBy: mongoose.Types.ObjectId(id),
                patient_id: p_id,
              },
            },
          ]
        : [
            {
              $match: {
                createdBy: mongoose.Types.ObjectId(id),
              },
            },

MongoDB select where in array of _id?

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