Thing I've learned today

mongo_console.js

// way to shoot your own leg
var q = db.some_collection.find({something: "awful"});
q.forEach(function(o) {print(o.foo)}) //this will print something affects map() too
q.forEach(function(o) {print(o.bar)}) //will print nothing
/* because */ q.hasNext() // == false after first call

//right way is to reassign q or don't use it at all
db.some_collection.find({something: "awful"}).forEach(function(o) {print(o.foo)}) //will work
db.some_collection.find({something: "awful"}).forEach(function(o) {print(o.bar)}) //will print stuff too