Getting person account properties from respective User

Question

if I have a user that has "plugged" a person account through the User.ContactId,

Account a = handleAccount(create, u, attributes);    // a    gets an account object       
Id accountId = a.Id;     
User U  ....        
U.ContactId = [select PersonContactId  FROM account where ID =: accountId].PersonContactId; 

How can I do to refer to any of the person account properties from User?

Is there something like U.ContactId__r.personemail? 

Answer 1

Since the ContactID is not a true reference ,you will have to query the information back for users

map<Id,user> mapIdByuser = new map<Id,User>([Select Id,email from User where ContactId in :setContacts]);
map<Id,User> mapContactIdByUser = new map<Id,User>();
for(User u :mapIdByuser.values()){
     mapContactIdByUser.put(u.contactId,u);
}