codeigniter获取上一个和下一个博客页面链接

class Blog_model extends CI_Model {
    public function get_previous_link($current_id) {
        $this->db->select('id');
        $this->db->from('blog');
        $this->db->where('id <', $current_id);
        $this->db->order_by('id', 'desc');
        $this->db->limit(1);
        $query = $this->db->get();
        
        if ($query->num_rows() > 0) {
            $row = $query->row();
            return site_url('blog/view/'.$row->id);
        } else {
            return null;
        }
    }
    
    public function get_next_link($current_id) {
        $this->db->select('id');
        $this->db->from('blog');
        $this->db->where('id >', $current_id);
        $this->db->order_by('id', 'asc');
        $this->db->limit(1);
        $query = $this->db->get();
        
        if ($query->num_rows() > 0) {
            $row = $query->row();
            return site_url('blog/view/'.$row->id);
        } else {
            return null;
        }
    }
}

class Blog extends CI_Controller {
    public function view($id) {
        $this->load->model('Blog_model');
        
        // 获取当前博客页面链接
        $data['current_link'] = site_url('blog/view/'.$id);
        
        // 获取上一个博客页面链接
        $data['previous_link'] = $this->Blog_model->get_previous_link($id);
        
        // 获取下一个博客页面链接
        $data['next_link'] = $this->Blog_model->get_next_link($id);
        
        // 加载视图文件，并将链接数据传递给视图
        $this->load->view('blog_view', $data);
    }
}

<div class="pagination">
    <?php if ($previous_link): ?>
        <a href="<?php echo $previous_link; ?>">上一个</a>
    <?php endif; ?>
    
    <?php if ($next_link): ?>
        <a href="<?php echo $next_link; ?>">下一个</a>
    <?php endif; ?>
</div>