I can't get a simple id

[eluser]Sein Kraft[/eluser]
It doesn't work :S

Fatal error: Call to undefined method CI_DB_my::num_rows() in E:\server\htdocs\libelula\system\application\models\model_imageboard.php on line 48

I need the id of the latest record to insert in another table.

When I upload a image i assign an id (auto-increment in sql), then i need retrieve that id and insert in other table where the id is inserted with a tag system.

For Example:
I have a form with two inputs, one for the file and other for the tags who represent the image.

For the first instance I insert in the table (images) the data of the uploaded image.
Next I need retrieve the id of the uploaded image from the table (images) and get the tags from the second input of the form and save in the table (tags).

Code:

function insert($data)
    {
        
        //INSERT IMAGE IN IMAGES
        $user_id = '1';
        $user_ip = '127.0.0.1';
        $file_hash = 'myhash';
        
        $file_name = $data['file_name'];
        $file_ext = $data['file_ext'];
        $file_size = $data['file_size'];
        $file_width = $data['file_width'];
        $file_height = $data['file_height'];
        $file_source = $data['file_source'];
        $file_tag = $data['file_tag'];
        
        $data = array(
               'id' => 'NULL' ,
               'user_id' => $user_id,
               'user_ip' => $user_ip,
               'file_name' => $file_name,
               'file_hash' => $file_hash,
               'file_ext' => $file_ext,
               'file_size' => $file_size,
               'file_height' => $file_height,
               'file_width' => $file_width,
               'file_source' => $file_source
            );

        $this->db->insert('images', $data);
                      
        //INSERT TAGS

        $query = $this->db
        ->select('id')
        ->from('images')
        ->limit(1)
        ->order_by('id','desc');
                
        $data = array(
               'image_id' => $query ,
               'image_tag' => $file_tag
            );

        $this->db->insert('tags', $data);

    }

Function id() is a test function because I can't do this work.