我用下面代码编写模型：

public function generate_google(){
        $this->db->select('*'); // <-- There is never any reason to write this line!
$this->db->from('products');
$this->db->join('product_details', 'products.id = product_details.product_id');
$this->db->join('images', 'products.id = images.product_id');

$query = $this->db->get()->result_array();

    
$xml = '<root>';
foreach($query as $row){
  $xml .= '<item>
             <sku>'.$row['sku'].'</sku>
             <price>'.$row['price'].'</price>
             <stock>'.$row['stock'].'</stock>
             <title>'.$row['title'].'</title>
           </item>';
}
$xml .= '</root>';
$this->output->set_content_type('text/xml');
$this->output->set_output($xml);
        
        
    }

1.如何在浏览器中添加保存xml文件而不显示输出的选项？
1.最后如何添加规则WHERE products.stock >= 1？
@update请看下面是我的更新代码为model controller和view
sitemap_model.php

public function get_all_products() {
        $this->db->select('products.*, product_details.*, images.*')
        $this->db->from('products');
        $this->db->join('product_details','product_details.product_id = products.id');
        $this->db->join('images','images.product_id = products.id');
        $this->db->where('products.stock >=' 1);

        $query = $this->db->get();

        return $query->result_array();
    }

sitemap_controller.php

public function generate_google_post()
{
$this->load->model('sitemap_model');

$xml   = '<root>';
$query = $sitemap_model->get_all_products();

foreach ($query as $row) {
    $xml .= '<item>
        <sku>'.$row['sku'].'</sku>
        <price>'.$row['price'].'</price>
        <stock>'.$row['stock'].'</stock>
        <title>'.$row['title'].'</title>
    </item>';
}

$xml .= '</root>';

header('Content-type: text/xml');
header('Content-Disposition: attachment; filename="file.xml"');

echo $xml;
}

view.php

<?php echo form_open('sitemap_controller/generate_google_post'); ?>
            
            <!-- /.box-body -->
            <div class="box-footer">
                <button type="submit" name="process" value="generate" class="btn btn-primary pull-right" style="margin-bottom: 5px;"><?php echo trans('download_sitemap'); ?></button>
                
            </div>
            <!-- /.box-footer -->

        <?php echo form_close(); ?><!-- form end -->

我不确定这个错误是从哪里来的，但是当我点击“生成”时，我得到了这个错误，我把它粘贴在评论中。