Sort Ember Object Array with Promises

I have a model model/person

{

  firstName: DS.attr( 'string'),
  lastName: DS.attr( 'string'),
  email: DS.attr( 'string' ),
}

and another model model/project

{

  name:            DS.attr( 'string' ),
  code:            DS.attr( 'string' ),
  startDate:       DS.attr( 'date' ),
  endDate:         DS.attr( 'date' ),
  users : DS.hasMany('person', {async: true}),

}

then i'm retrieving all the projects with as an array which contains ember objects. since the project -> users is async its a promise. and i want to sort that array using the first name of the person. when the data is arrived accordingly and re render the hbs that is using the list

i have a computed property called

renderProjects = computed ('model.projects.[]')
{
 // trying to sort in here but data is not avaiable so its not getting sorted
}