mongodb query promise sample

http://mongoosejs.com/docs/api.html#promise_Promise

Promise#then(

onFulFill

, 

onReject

)

Creates a new promise and returns it. If 

onFulfill

 or 

onReject

 are passed,
they are added as SUCCESS/ERROR callbacks to this promise after the nextTick.

Parameters:

onFulFill

 <Function>

onReject

 <Function>

Returns:

<Promise> newPromise

See:

promises-A+
mpromise#then

Conforms to promises/A+ specification.

Example:

var promise = Meetups.find({ tags: 'javascript' }).select('_id').exec();
promise.then(function (meetups) {
var ids = meetups.map(function (m) {
return m._id;
});
return People.find({ meetups: { $in: ids }).exec();
}).then(function (people) {
if (people.length < 10000) {
throw new Error('Too few people!!!');
} else {
throw new Error('Still need more people!!!');
}
}).then(null, function (err) {
assert.ok(err instanceof Error);
});