Form validation in codeigniter does not seem DRY

When you said validate more than one _post variable, I thought you were talking about more than one $_POST dataset. Reading your first provided link I now see what you mean.

You need two values from your $_POST dataset to validate a specific value. Creating a custom validation rule should do the trick.

I would suggest extending the validation class and adding your custom method.

Example:

PHP Code:

public function my_custom_validation($validate_this, $_post_key) {
    $ci =& get_instance();
    // do your validation
    $post_fields = explode('.', $_post_key);
    // Set the fieldnames
    foreach($post_fields as $key) {
        $$key = $this->ci->input->post($key);
    }
} 


To use it do:

PHP Code:

$this->form_validation->set_rules('url', 'URL', 'trim|xss_clean|my_custom_validation[post_key]'); 


You add my_custom_validation to your rules and between the [] you place the name of the field or fields that must also be used for the validation. When using multiple fields use a . to seperate the names

You should now be able to validate more than one post value within the same validation method