MongoDB: find by one objectId in array

Question

I'm having trouble with query the DB, I want to get all element that the have for example: admin "54bd13864ec56c7c12310a79" in the admins array,

tried it with "$in" but it didn't worked, could it be related to the fact that its an ObjectId?

trainerId = '54bd13864ec56c7c12310a79'
GroupSchema.find({'admins': { $in: [ trainerId ] }}

This is my db:

{
   "_id" : ObjectId("54b93e8e3801ae381e3433be"),
   "groupName" : "Developers Groups",
   "createdBy" : "Ido",
   "creationDate" : "Jan 16 2015",
   "users" : [ 
       ObjectId("54b932c7ac3ec34a85e6246c")
   ],
   "admins" : [ 
       ObjectId("54b932c7ac3ec34a85e6246c"), 
       ObjectId("54bd13864ec56c7c12310a79")
   ],
   "__v" : 0
}

The Schema model is:

module.exports = mongoose.model('Groups' ,
{
    groupName: String,
    createdBy: String,
    creationDate: String,
    admins: [{ type : mongoose.Schema.Types.ObjectId, ref: 'Users' }],
    users: [{ type : mongoose.Schema.Types.ObjectId, ref: 'Users' }]
}
);

did you solve this answer? I have the exact same issue. I too want to search for object id which is in array. were you able to solve this problem? — Aadi
– Aadi, Commented Oct 6, 2021 at 8:43

chridam · Accepted Answer · 2015-04-16 14:34:35Z

8

Convert the id string to ObjectId:

var mongoose = require('mongoose'),
    trainerId = '54bd13864ec56c7c12310a79';
var id = mongoose.Types.ObjectId(trainerId);

GroupSchema.find({'admins': id });

answered Apr 16, 2015 at 14:34

chridam

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3 Comments

Aviram Fireberger Over a year ago

Well you got my in the way to the solution: That was: var trainerId = mongoose.Schema.Types.ObjectId(trainerId); GroupSchema.find({'admins': { $in: [ trainerId ] }} I marked your as the corrent answer thanks :)

shmup Over a year ago

@AviramFireberger I'm not sure why you had to use $in, as just using {admins: ObjectId('EXAMPLE')} should have worked, too.

Aviram Fireberger Over a year ago

@badteeth I really can't remember why... it was 7 years ago lol

Maxim Pontyushenko · Accepted Answer · 2015-04-16 14:34:19Z

5

This is ObjectId:

ObjectId("54bd13864ec56c7c12310a79")

and this is string:

trainerId = '54bd13864ec56c7c12310a79'

So maybe you should use ObjectId in your query.

answered Apr 16, 2015 at 14:34

Maxim Pontyushenko

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Comments

Joseph Blair · Accepted Answer · 2015-04-16 14:27:27Z

4

If I understand your question correctly, you probably want to use $elemMatch for this. $in should be used when you want to check if a non-array field is equals one of the values specified in the array you pass to $in.

answered Apr 16, 2015 at 14:27

Joseph Blair

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3 Comments

Aviram Fireberger Over a year ago

How can I used the $elemMatch in case of ObjectId? I tried : db.groups.find('admins' : { $elemMatch : {'54b932c7ac3ec34a85e6246c'} } ) but it didn't work as well

Prusse Over a year ago

try { $elemMatch : { $eq: '54b932c7ac3ec34a85e6246c'} }

raner Over a year ago

{ $elemMatch : { $eq: ObjectId("54b932c7ac3ec34a85e6246c")} } should work

qianjiahao · Accepted Answer · 2015-04-16 14:33:54Z

2

If i understand your question correctly,you probably can try the $unwind in aggregation,separate the element in admins.

answered Apr 16, 2015 at 14:33

qianjiahao

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Comments

Jason Cust · Accepted Answer · 2015-04-16 15:29:58Z

2

It looks like you want to match the parent document with a subdocument id. You can either use a simple query:

GroupSchema.find({'admins._id': trainerId}})

Or you could use $elemMatch, but as the doc says it's not necessary: If you specify only a single condition in the $elemMatch expression, you do not need to use $elemMatch.

GroupSchema.find({admins: {$elemMatch: {_id: trainerId}}})

As far as casting the string value to an ObjectId, mongoose will automatically do this for you internally.

edited Apr 16, 2015 at 15:29

answered Apr 16, 2015 at 15:16

Jason Cust

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2 Comments

Aviram Fireberger Over a year ago

I dont get an exception in both of them but I do get 0 results. I double check the Id... it is correct. both: ".find({'admins': {$elemMatch: {'_id': '54b932c7ac3ec34a85e6256c'}}})" and ".find({'admins._id': '54b932c7ac3ec34a85e6256c'}})" didn't worked

Jason Cust Over a year ago

What is GroupSchema? Convention uses the internal model name as the model object name: Group. That said, it's very odd that you have to cast the string value to an ObjectId if you are using mongoose. Can you post which version of mongoose you are using and what GroupSchema is?

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