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?
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6 Answers
Easy :)
db.collection.find( { _id : { $in : [1,2,3,4] } } );
taken from: https://www.mongodb.com/docs/manual/reference/operator/query/in/#mongodb-query-op.-in
5 Comments
Rafal Pastuszak
Do we still get benefits of indexing? IDs in that case are passed as plain strings...
Petr Brazdil
You do. However time complexity is linear (n), not logarithmic/constant. Without index it would be n^2.
Guig
Is it not
O(log(n) * m) where n is the size of the collection and m is the number of ids passed ?
Pax Beach
U have to use ObjectId function, if "_id" is the ID object — {_id: {$in: [ObjectId("5a633609670aeb6f93b88b23")]}}
Carcigenicate
And nowadays, you need
new ObjectId(...).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" : { $in : [ObjectId('1'),ObjectId('2')] } }
Note: objectId in string has 24 length.
Comments
You can try this
var ids = ["5883d387971bb840b7399130","5883d389971bb840b7399131","5883d38a971bb840b7399132"];
var oids = [];
ids.forEach(function(item){
oids.push(new ObjectId(item));
});
.find({ _id: {$in : oids}})
1 Comment
Andrei Charnyshou
Thanks. Remember to define ObjectID like this: var ObjectId = require('mongodb').ObjectID;
In this code list is the array of ids in user collection
var list = ["5883d387971bb840b7399130","5883d389971bb840b7399131","5883d38a971bb840b7399132"]
.find({ _id: {$in : list}})
2 Comments
Pax Beach
The code is not working. It seems have to set IDs as ObjectId("5883d387971bb840b7399130")
Vikalp Jain
How do we do set them to ObjectIds programmatically? I tried the approach suggested by @klipmode in one of the answers, but that does not work.
The query should be something like this:
db.collection.find( {
"_id": {
"$in": [
"475B9A5029D21",
"385D808029D81",
"C3463BD029DBB",
"B839DB5029FFF"
]
}
} );
Comments
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),
},
},
