how to catch database errors in model

If you have db_debug set in your database config, you won't really get a chance to catch the errors.

$this->db->_error_message() only works in CI2. CI3 does include an error() method in the db class to get the most recent error, if any have occurred:
http://www.codeigniter.com/user_guide/da...ing-errors

So, you would do something like this:

PHP Code:

public function deal_citys($deal_id)
{
    $query = $this->db->query("select deal_location from deal where deal_id=$deal_id");
    if ($query->num_rows() > 0) {
        return $query->row()->deal_location;
    }

    // It may be that $deal_id wasn't found, 
    // but we can check for an error, anyway.
    $error = $this->db->error();

    // If an error occurred, $error will now have 'code' and 'message' keys...
    if (isset($error['message'])) {
        return $error['message'];
    }

    // No error returned by the DB driver... 
    return null;
} 


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