echo $BRAIN_STUFF

Suppose you need to apply some filters to your MongoDB query, for example to extract some _ids that match a regex condition. This is the way to do that:

Query query;
query.addCriteria(Criteria.where("_id").in(IDs).and(query_field).regex(".*" + query_value + ".*", "i"));

In this example I used the Query (see here) and Criteria (see here) classes

And, this is the query you can use in mongoDB (Robomongo* or command line):

Query: { 
	"_id" : { "$in" : [ "ID1" , "ID2" , "ID3" ]} , 
	"detail.medicationBrandName" : { "$regex" : ".*x.*" , "$options" : "i"}}, 
	Fields: null, Sort: { "medicationGenericName" : -1}
}

*Robomongo: is a shell-centric cross-platform open source MongoDB management tool (i.e. Admin GUI). Robomongo embeds the same JavaScript engine that powers MongoDB’s mongo shell. You can download it here.