MongoDB: $in with an ObjectId array

Question

Just a quick question about something I've just experienced and I'm still thinking about why:

mongos> db.tickets.count({ "idReferenceList" : { "$in" : [ { "$oid" : "53f1f09f2cdcc8f339e5efa2"} , { "$oid" : "5409ae2e2cdc31c5aa0ce0a5"}]}});

0

mongos> db.tickets.count({ "idReferenceList" : { "$in" : [ ObjectId("53f1f09f2cdcc8f339e5efa2") , ObjectId("5409ae2e2cdc31c5aa0ce0a5")]}});

2

I thought that both $oid and ObjectId spelling formats where exactly the same for MongoDB. Does anyone know why with the first query return 0 results and with the second one is returning 2 (the right answer)?

Furthermore, I'm using Morphia framework which uses MongoDB Java driver to interact with MongoDB. I've realised that there exists a problem by searching with $in operator in ObjectIds arrays over fields that are not _id by executing this lines of code:

List< ObjectId > fParams = new ArrayList< ObjectId >();

fParams.add(...);

Query<Ticket> query = genericDAO.createQuery();

query.field("idReferenceList").in(fParams);

result = genericDAO.find(query).asList();

Thank you very much in advance.

Regards,

Luis Cappa

genericDAO.find(query).asList(); // can you do this and check. ? Wjat is the filter you are using in this.createQuery(filter), by the way. — BatScream
– BatScream, Commented Sep 11, 2014 at 9:05
Sorry, it was just a typo error. This 'createQuery' method is an internal method that creates a Query by filtering by the fParams list. In short words, genericDAO.Find(this.createQuery(filter)) is the same as genericDAO.find(query). Sorry about that. — lcappa
– lcappa, Commented Sep 12, 2014 at 9:19

BatScream · Accepted Answer · 2014-09-11 07:13:48Z

8

Both these formats are valid representations of an object id in MongoDB, according to the documentation,

http://docs.mongodb.org/manual/reference/mongodb-extended-json/

and they represented differently in the two modes,

    Strict Mode         mongo Shell Mode
    -----------         ----------------

   { "$oid": "<id>" }  ObjectId( "<id>" )

So, to query fields which contain objectid, from the shell/console mode, you need to use ObjectId("<id>"). Which is the syntax to be followed in the mongo shell mode.

Hence the query:

db.tickets.count({ "idReferenceList" : { "$in" : [ ObjectId("53f1f09f2cdcc8f339e5efa2") , ObjectId("5409ae2e2cdc31c5aa0ce0a5")]}});

would return you row count.

Now to do it via the Java API,

You need to do it as below:

String[] ids = {"53f1f09f2cdcc8f339e5efa2","5409ae2e2cdc31c5aa0ce0a5"};
ObjectId[] objarray = new ObjectId[ids.length];

for(int i=0;i<ids.length;i++)
{
    objarray[i] = new ObjectId(ids[i]);
}

BasicDBObject inQuery = new BasicDBObject("$in", objarray);
BasicDBObject query = new BasicDBObject("idReferenceList", inQuery);
DBCursor cursor = db.collection.find(query);
while(cursor.hasNext())
{
    DBObject doc = cursor.next();
    // process the doc.
}

edited Sep 11, 2014 at 7:13

answered Sep 10, 2014 at 15:56

BatScream

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8 Comments

lcappa Over a year ago

The thing is that I'm not querying to "_id" field, but to "idReferenceList", which is another different field defined with a field type of Array of objectIds. As you can see, It doesn't work...

BatScream Over a year ago

objectid representation remains the same irrespective of the field it is present in. Will update my answer. I just gave an reference to the _id field.

lcappa Over a year ago

But with the "$oid" representación It doesn't work. Did you test it? Just save two test documents via shell and try it yourself. The problem anyway is that I'm using MongoDB Java driver and I cannot spell by myself directly the "ObjectId" query format.

BatScream Over a year ago

Yes, read my answer carefully. $oid representation will not work in the shell because it is the syntax to be followed in a strict mode.

lcappa Over a year ago

So... any idea to solve this problem? Because as I told you I'm using MongoDB Java driver and query spelling is not as flexible as desired.

|

totheskyer · Accepted Answer · 2019-04-10 20:25:03Z

4

I faced the same issue. I resolved like this way.

db.collection('post').find({ 'postIds': { $elemMatch: { $in:
deletedPosts.map(_post => {ObjectId(_post._id)}) } } })

answered Apr 10, 2019 at 20:25

totheskyer

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