MongoDB: $in with an ObjectId array
Just a quick question about something I've just experienced and I'm still thinking about why:
mongos> db.tickets.count({ "idReferenceList" : { "$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 $in operator in ObjectIds arrays over fields that are not _id by executing this lines of code:
List< ObjectId > fParams = new ArrayList< ObjectId >();
fParams.add(...);
Query<Ticket> query = genericDAO.createQuery();
query.field("idReferenceList").in(fParams);
result = genericDAO.find(query).asList();
Thank you very much in advance.
Regards,
Both these formats are valid representations of an object id in MongoDB, according to the documentation,
http://docs.mongodb.org/manual/reference/mongodb-extended-json/
and they represented differently in the two modes,
Strict Mode mongo Shell Mode
----------- ----------------
{ "$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.
}
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