Mongo find by regex: return only matching string

Question

My application has the following stack:

Sinatra on Ruby -> MongoMapper -> MongoDB

The application puts several entries in the database. In order to crosslink

Answer 1

I don't know if I understand.

db.yourColl.aggregate([
{
    $match:{"yourKey":{$regex:'[a-zA-Z0-9]', "$options" : "i"}}
},
{
    $group:{
        _id:null,
        tot:{$push:"$yourKey"}
    }
}])

If you don't want to have duplicate in totuse $addToSet