Скачать или смотреть Dynamically Add or Remove WTForms Validators in Flask

Discover how to dynamically add or remove WTForms validators in Flask for customizable form validation based on user data.
---
This video is based on the question https://stackoverflow.com/q/72598178/ asked by the user 'squidg' ( https://stackoverflow.com/u/13534073/ ) and on the answer https://stackoverflow.com/a/72613434/ provided by the user 'pjcunningham' ( https://stackoverflow.com/u/2800058/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Dynamically Add or Remove WTForms validators in Flask

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Dynamically Add or Remove WTForms Validators in Flask

As developers, we often encounter situations where the validation requirements of our forms can change based on user interactions or data. In Flask, using WTForms for form handling is a popular choice. One frequently asked question is: How can we dynamically add or remove validators in a WTForms form? In this guide, we'll explore this topic in depth and provide a step-by-step solution to achieve this functionality in your Flask application.

Understanding the Problem

Imagine you have a form with an email field that should be mandatory based on user data — perhaps they are a new user or an existing one. In such cases, maintaining a fixed set of validators may not always work. Instead, you need the ability to dynamically adjust the validators associated with form fields.

For example, consider the following basic form definition:

[[See Video to Reveal this Text or Code Snippet]]

With this validation structure, you might want to remove the required email validation based on certain conditions. While you might have tried removing validators using methods like del form.email.validators or form.email.validators.remove, these approaches may not yield the desired results.

The Solution: Dynamic Form Subclassing

The recommended approach to dynamically manipulate WTForms validators is through subclassing the form within your view. Here are the steps to accomplish this:

Step 1: Defining the Base Form

Start by defining your base form with any initial validators:

[[See Video to Reveal this Text or Code Snippet]]

In this base form, we already have a first_name field that has two validators: one requiring input and another enforcing a minimum length.

Step 2: Creating a Dynamic Subclass

In your view, create a dynamic subclass of the form and remove the necessary validators. Here’s how you can do it:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Putting It All Together in a Flask Route

Here's an example of how you might implement this in a Flask route:

[[See Video to Reveal this Text or Code Snippet]]

Step 4: Setting Up Templates

Make sure you define your templates for rendering the form and displaying errors:

[[See Video to Reveal this Text or Code Snippet]]

Real-World Example

The complete application code looks like this:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Dynamically managing WTForms validators in Flask allows you to create forms that respond to user input and requirements. By subclassing your forms and manipulating validators as shown, you can ensure your application provides a flexible and user-friendly experience.

Now, when building complex applications in Flask, remember that you can dynamically add or remove validators based on specific conditions, improving both the maintainability and usability of your application.

For more Flask tips, stay tuned to our blog!