Save user activation hash

hi , how can i save the user activation hash on db ?

this is a part of my controller's method :

PHP Code:

$post = $this->request->getPost();

            // generate random hash for email verification (40 char string)
            $user_activation_hash = sha1(uniqid(mt_rand(), true));

            $post['user_activation_hash'] = $user_activation_hash;

            $res=$model->save($post); 


every field is stored but user_activation_hash in db are null

Find the error protected $allowedFields user_activation_hash was write bad ...

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hi , how can i save the user activation hash on db ?

this is a part of my controller's method :

PHP Code:

$post = $this->request->getPost();

            // generate random hash for email verification (40 char string)
            $user_activation_hash = sha1(uniqid(mt_rand(), true));

            $post['user_activation_hash'] = $user_activation_hash;

            $res=$model->save($post); 


every field is stored but user_activation_hash in db are null

Find the error protected $allowedFields user_activation_hash was write bad ...

Now i cannot update the data , this is my method inside model :

PHP Code:

function confirm_registration($user_activation_hash){

      //search user with user_activation_hash=$user_activation_hash
      $query=$this->where('user_activation_hash', $user_activation_hash)->get();

      $user=$query->getRow();

      //if ther'arent record
      if(!$user){

          return FALSE;
      }


      $data = array(
              'id_stato_users'=>2,
              'user_activation_hash' => NULL
            );

      $this->where('id', $user->id);
      $this->update($data);


      if($this->affectedRows()){

          return TRUE;

      }else{

          return FALSE;

      }

         
    } 


But have this error : There is no data to update. [url=https://www.google.com/search?q=CodeIgniter%5CDatabase%5CExceptions%5CDataException+There+is+no+data+to+update.][/url]