Ember model access to belongsTo property return null

I have a model Person with this property : address_fk: DS.belongsTo('address') refering to an Address model.

In the adress model, there are several properties such as zip_code , building ...

My goal is to create a computed property in Person to display the full address by accessing this.get('address_fk.zip_code') but it returns me undefined

I'm surely missing something here but I really don't know what.

Update : Problem solved, here is how :

adresse: computed('adresse_fk', function() {
return DS.PromiseObject.create({
  promise: this.get('adresse_fk').then((adresse) => {
    return adresse.get('escalier_etage_appartement') + ' ' + adresse.get('batiment') + ' ' + adresse.get('numero_nom_voie') + ' ' + adresse.get('code_postal') + ' ' + adresse.get('commune_fk.nom')
  })
});

}),

you are defining the computed property on the Person model. The computed property may return a PromiseObject for the address. You could try these two things -

1 Check for the presence of adresse_fk

// Person model
adresse: Ember.computed('adresse_fk', function() {
if this.get('adresse_fk'){
  return this.get('adresse_fk.escalier_etage_appartement') + ' ' 
   + this.get('adresse_fk.batiment') + ' ' + 
   this.get('adresse_fk.numero_nom_voie')
}

2 Use then to resolve promises

// Person model
adresse: Ember.computed('adresse_fk', function() {
this.get('adresse_fk').then( function(address){
  return address.get('escalier_etage_appartement') + ' ' 
   + address.get('batiment') + ' ' + 
   address.get('numero_nom_voie')
 }
}

I have not tested them but they should work.