Make nested queries in MongoDB 3.0.7 - mongodb

Question

I have sub-events belonging to events belonging to an user, and I know the user's username - how do I get a list of the sub-events?
Is this going in the right direction? Or is it completely off?
db.subevents.find({_id: {$in:
db.events.find({_id: {$in:
db.users.find({"username":"userx"},{_id:1})}},{_id:1})}})
Edit: Here is a sample of the data structure:
/* Event */
{
"_id" : "XjhAqqNBkezKY3mdN",
"name" : "My event",
"userId" : "FiKsAAAgBb7cNoPH7"
}
/* Subevent */
{
"_id" : "WkYAqBXNpJryp7rum",
"name" : "The subevent",
"eventId" : "hQXNzX3jbWppbAYFH"
}
/* User */
{
"_id" : "RTHh5srhLMQp625zF",
"username" : "userx"
}

Answer 1

Following profesor79's advice to use three different calls, I put together this solution to get all the sub-events belonging to the user:
var userIds = db.users.find({"username":"userx"}).map(function(user) {
return user._id;
});
var eventIds= db.events.find({userId: {$in:userIds}}).map(function(event) {
return event._id;
});
db.subevents.find({eventId:{$in:eventIds}});

Answer 2

The only way is to make 3 ddifrent calls in mongo 3.0.7
GetUSerData
GetEventData
GetSubEventData
As you have relational schema here - this should be easy.
You could improve schema and remove subEvent collection by embedding subEvents documents into one events document
EDIT
/* Event */
{
"_id" : "XjhAqqNBkezKY3mdN",
"name" : "My event",
"userId" : "FiKsAAAgBb7cNoPH7"
"subewents" : [{
"_id" : "WkYAqBXNpJryp7rum",
"name" : "The subevent",
"eventId" : "hQXNzX3jbWppbAYFH"
}, {
"_id" : "WkYAqBXNpJryp7rum2",
"name" : "The subevent2",
"eventId" : "hQXNzX3jbWppbAYFH"
}, {
"_id" : "WkYAqBXNpJryp7rum",
"name" : "The subevent",
"eventId" : "hQXNzX3jbWppbAYFH"
}
]
}
/* User */
{
"_id" : "RTHh5srhLMQp625zF",
"username" : "userx"
}