如何使用laravel 5.7中的eager-load从子模型的外键实例中获取父值

Question

i have four models -User -Question -Answer -Comment

the User model contains

public function questions(){
        return $this->hasMany(Question::class);
 }
public function answers(){
        return $this->hasMany(Answer::class);
}
public function comments(){
        return $this->hasMany(Comment::class);
}

the Question model contains

public function users(){
        return $this->belongsTo(User::class,'user_id','id');
}
public function answers(){
        return $this->hasMany(Answer::class);
}
public function comments(){
        return $this->hasMany(Comment::class);
}

//the question table has user_id

the Answers model contains

public function questions(){
        return $this->belongsTo(Question::class,'user_id','id');
}
public function users(){
        return $this->belongsTo(User::class);
}
public function comments(){
        return $this->hasMany(Comment::class);
}

//the answers table has user_id,question_id

the Comment model contains

public function questions(){
        return $this->belongsTo(Question::class);
}
public function users(){
        return $this->belongsTo(User::class);
}
public function answers(){
        return $this->belongsTo(Answer::class);
}

//the answers table has user_id,question_id,answer_id

whenever access the Question model i can get access User,Answer,Comment related to that Question

but i want to get the details of the user that answers the question as well as the details of the user that commented on an answer.

this is my controller

public function show($slug){    
        $questionData = Question::with('users','answers','comments')->where('slug',$slug)->first();
         return view('questions.single',compact('questionData'));
}

but wheneva i do

@foreach($questionData->answers as $answer)
    $answer->user_id;
   //it retuns only the user_id from the answers table
   //how can i turn this to the username
@endforeach

i want to get the username of the user who answerd the question, as well as the username of the user that commented on the answer