Laravel:在一个查询中添加来自另一个相关表的值

class User extends Model
{
    public function posts()
    {
        return $this->hasMany(Post::class);
    }
}

class Post extends Model
{
    public function user()
    {
        return $this->belongsTo(User::class);
    }
}

$posts = Post::with('user')->get();

foreach ($posts as $post) {
    echo $post->user->name; // 这里会触发额外的查询
}

$posts = Post::with('user')->get();

foreach ($posts as $post) {
    echo $post->user->name; // 这里不会触发额外的查询
}

$post = Post::find(1);
echo $post->user->name; // 如果用户不存在，这里会抛出异常

$post = Post::find(1);

if ($post->user) {
    echo $post->user->name;
} else {
    echo 'User not found';
}

// User.php
class User extends Model
{
    public function posts()
    {
        return $this->hasMany(Post::class);
    }
}

// Post.php
class Post extends Model
{
    public function user()
    {
        return $this->belongsTo(User::class);
    }
}

// 查询并预加载关联数据
$posts = Post::with('user')->get();

foreach ($posts as $post) {
    echo $post->title . ' by ' . $post->user->name;
}