someSchema.pre('save', function(next){
  asyncFunction(function(){
    this.sub.value = 'something'
    next()
  })
})

some.Schema.pre('save', function(next){
  asyncFunction(function(){
    next('something')
  });
});
some.Schema.pre('save', function(next, value){
  this.sub.value=value
  next()
})

someSchema.pre('save', function(next){
  x = this
  asyncFunction(function(){
    x.sub.value = 'something'
    next()
  })
})

someSchema.pre('save', function(next){
  var self = this;
  asyncFunction(function(){
    self.sub.value = 'something'
    next()
  })
})