Eloquent：根据表关系计算行数

I have no idea how to solve this problem using Laravel Eloquent. So, I posted my question here.
I have tables like this:

+-------------+  +------------------------+
| POSTS       |  | COMMENTS               |
|-------------|  |------------------------|
| id  | title |  | id | text    | post_id |
|-----+-------|  |----+-------------------|
| 1   | A     |  | 1  | Lorem   | 1       |
| 2   | B     |  | 2  | Ipsum   | 1       |
+-------------+  | 3  | Dolor   | 1       |
                 | 4  | Sit     | 1       |
                 | 5  | Amet    | 2       |
                 | 6  | Lorem 2 | 2       |
                 +------------------------+

I currently have 2 models, Post model

class Post extends Model
{
    public function comment() {
        $this->hasMany('App\Comment');
    }
}

and Comment model

class Comment extends Model
{
    public function comment() {
        $this->belongsTo('App\Post');
    }
}

The question is, What should I do on the controller so I can make each post has a comment count result? Or simply, just like the table below.

+-----------------------------------------+
| COMMENT COUNT                           |
|-----------------------------------------|
| posts.id | count(comments.post_id) AS n |
|----------+------------------------------|
| 1        | 4                            |
| 2        | 2                            |
+-----------------------------------------+

Thanks.

You forgot to return the relationships. So, the models should be defined as:

class Post extends Model
{
    public function comments()
    {
        return $this->hasMany('App\Comment');
    }
}

class Comment extends Model
{
    public function post()
    {
        return $this->belongsTo('App\Post');
    }
}

Now you can count the post comments as:

echo $post->comments()->count();

or even

echo $post->comments->count();

The difference between these 2 methods is that the latest one is getting and caching the post comments as well.