How to validate fields with the Rules module?

Question

I have created a Rule with the Rules module to validate the form on submission.

I try to compare the values of two fields to ensure one not higher than the other. But I couldn't find the appropriate Rules Actions to stop the form submission and prompted an error message.

Please advise.

Event: After saving new content of type Article

Condition: Data comparison Parameter: Data to compare: [node:field-price-A], Operator: is greater than, Data value: [node:field-price-B]

Actions: ??

Answer 1

It sounds like you don't have the supporting module Rules Forms: https://www.drupal.org/project/rules_forms

This module adds form validation for existing (core) forms and custom forms from contrib modules.

The documentation states that Rules Forms can:

Validate the values of form elements during form validation. Set form errors when rule-based validation fails.

Answer 2

Have a look at the Rules Forms Support module. More details about it (from its project page):

Rules Forms Support provides a Rules based method for controlling forms and their elements. The module can be used to alter any form provided by Drupal core or contributed modules. Change element titles, descriptions, weights, and more, or validate form data and set form errors. Rules forms saves time and cost by affording site builders the ability to monitor and alter forms without the need to implement a custom module.

For help getting started with Rules Forms Support, please see the module documentation.

Features

• Activate events for form creation, validation, and submission on a form-by-form basis.
• Target individual form elements or the entire form in conditions and actions.
• Manipulate the attributes of a form element like title, description, weight, and more.
• Validate the values of form elements during form validation.
• Set form errors when rule-based validation fails.
• Redirect users to a different page upon viewing or submitting a form.
• Examine the attributes of elements in active forms with the element inspection tool.

Especially the "Set form errors when rule-based validation fails" should help to address your question.

More details about how to use this module can be found in the community documentation "Altering & validating forms".