Get Specific Columns Using “With()” Function in Laravel Eloquent

I have two tables, User and Post. One User can have many posts and one post belongs to only one user.

In my User model I have a hasMany relation…

public function post(){
    return $this->hasmany('post');
}

And in my post model I have a belongsTo relation…

public function user(){
    return $this->belongsTo('user');
}

Now I want to join these two tables using Eloquent with() but want specific columns from the second table. I know I can use the Query Builder but I don’t want to.

When in the Post model I write…

public function getAllPosts() {
    return Post::with('user')->get();
}

It runs the following queries…

select * from `posts`
select * from `users` where `users`.`id` in (<1>, <2>)

But what I want is…

select * from `posts`
select id,username from `users` where `users`.`id` in (<1>, <2>)

When I use…

Post::with('user')->get(array('columns'....));

It only returns the column from the first table. I want specific columns using with() from the second table. How can I do that?