Using $in on multiple object ids

Question

I am running into problems deriving the correct MongoDB query. I am trying to formulate a query using the find operation that will retrieve multiple specified ids at once. Note that I cannot use ObjectId() functions. I need to use plain operators like $or, $and, $in, etc.

The dataset in MongoDB has rows that look like the following:

{
 "_id": {
  "$oid": "123"
 },
 "someField": "hello"
 ...
}
{
 "_id": {
  "$oid": "456"
 },
 "someField": "hello"
 ...
}

I have been able to use $or successfully in the following way, but since the MongoDB documentation suggests using $in over $or in terms of performance, I'd like to know how to do this using $in:

{ $or: [{ "_id": {   "$oid": "123"   }  },{ "_id": {   "$oid": "456"}}]}

I have tried the following queries, but none of them have returned any results:

{ "_id":  { $in: ["123", "456"] } }
{ "_id": { $in: [  "$oid": "123","$oid": "456"  ]} } 
{ "_id.$oid":  { $in: ["123", "456"]  }   }

As a last note, I cannot use any queries that completely isolate the object ids, as I am querying for the "someField" field of every matched object id as well.

Bertrand Martel · Accepted Answer · 2016-07-27 20:41:48Z

1

You almost had it :

{ "_id": { $in: [  "$oid": "123","$oid": "456"  ]} } 
should read
{ "_id":{ $in:[{"$oid":"123"},{"$oid":"456"}]}}

You pass in an array but because you are searching the _id field you need to send {"$oid":"oid_value"} for each item

edited Jul 27, 2016 at 20:41

Bertrand Martel

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answered Jul 27, 2016 at 18:34

Kirk Diggler

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