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I have a process that returns a list of String MongoDB ids,

[512d5793abb900bf3e20d012, 512d5793abb900bf3e20d011]

And I want to fire a single query to Mongo and get the matching documents back in the same order as the list.

What is the shell notation to do this?

Ry-
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Will
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4 Answers4

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After converting the strings into ObjectIds, you can use the $in operator to get the docs in the list. There isn't any query notation to get the docs back in the order of your list, but see here for some ways to handle that.

var ids = ['512d5793abb900bf3e20d012', '512d5793abb900bf3e20d011'];
var obj_ids = ids.map(function(id) { return ObjectId(id); });
db.test.find({_id: {$in: obj_ids}});
Asclepius
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JohnnyHK
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    This is working perfectly but i have an other query where i want only one record for the list of ids what should i do for that ? – Shashank Dubey Dec 24 '20 at 10:18
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    how can i get ids in an array from this : { "_id" : ObjectId("611b96a6699005a8f561fe52") }, { "_id" : ObjectId("611b96a2699005a8f561fe51") } – Youssef Boudaya Aug 17 '21 at 22:12
  • This works pretty well, but there is one issue with that. If you pass [ObjectId("id1", "id3", "id2")] and if in the database the order of records is "id1", "id2", "id3", it will return them into the latter order. What if I want it to return them into the exactly the same order as the ids array ? – Vitomir Aug 03 '23 at 12:28
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This works fine for me in Robo 3T. No need to create any object and just use the list of ids.

db.getCollection('my_collection').find({'_id':{$in:['aa37ba96']}})
Aminah Nuraini
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    I'm using pymongo in Python 3.8 and had to put quotes around `$in` in order to make it pass the linter and actually run. – HK1 Nov 15 '22 at 16:10
  • Is it scalable for very long list? For example: suppose I have a list of 50-100 ids and then I try to use `$in` to find all the matching documents. Or should I find another way? – Chetan Goyal Dec 12 '22 at 15:51
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If your final purpose is to get the document with the order by your pre-get ids list, you can just convert the query result into mapping(id as key, doc as value) , and then traverse the ids list to get the doc.

jianpx
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    I'm after the query that will return the results...? Code example would be much appreciated. – Will Feb 27 '13 at 03:39
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// categoryId comma separated "5c875c27d131b755d7abed86,5c875b0ad131b755d7abed81" in request

var ids= req.body.categoryId.split(','); 

db.test.find({ categoryId: { $in: ids } });
Sudhir Kushwaha
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    Does not answer the question. The question clearly shows an **array** and not a string. If you had something else to add on a **different** note, you could have [asked a new question](https://stackoverflow.com/questions/ask) and posted your own response. Adding *unrelated* answers to existing questions is not necessary. – Neil Lunn Oct 02 '19 at 09:49