print the name where value is in mongo db code example

Example 1: mongodb findmany

model.find({
    '_id': { $in: [
        mongoose.Types.ObjectId('4ed3ede8844f0f351100000c'),
        mongoose.Types.ObjectId('4ed3f117a844e0471100000d'), 
        mongoose.Types.ObjectId('4ed3f18132f50c491100000e')
    ]}
}, function(err, docs){
     console.log(docs);
});

Example 2: mongo find documents that have a certain key

db.coll.find({"mykey":{'$exists': 1}})