Created question in FIWARE Q/A platform on 08-09-2015 at 16:09
Please, ANSWER this question AT http://stackoverflow.com/questions/32459956/mongodb-aggregation-using-groovy-language

Question:
MongoDb: Aggregation using Groovy language

Description:
Iam using groovy scripting under SpagoBI. I want to use aggregation.
I want for example to execute the following aggregation:

db.myCollection.aggregate(
[
{
$group : {
_id : { day:

}

}
}
]
)

I tried:

DBObject projectFields = new BasicDBObject('$dayOfMonth',"recvTime");
DBObject project=new BasicDBObject('$project',projectFields)

DBObject groupFields = new BasicDBObject( "_id",project);

DBObject group = new BasicDBObject('$group', groupFields);

iterable = db.getCollection('myCollection').aggregate(group)

I got this error:

An unexpected error occured while executing dataset:

Any ideas?

Updates:
the query executed in Mongo shell

db['cygnus_/kurapath_enocean_power_enocean'].aggregate(
... [
... {
... $group : {
... _id : { day:

}
... }
... }
... ]
... );
{ "_id" :

}
{ "_id" :

}
{ "_id" :

}
{ "_id" :

}
{ "_id" :

}

the data stored in mongo db:

db['cygnus_/kurapath_enocean_power_enocean'].find()