Forms & Validations in Rails

Forms are where users hand your app messy, incomplete, or malicious input. Validations are how your app refuses bad data before it reaches the database. If you’re building AI features, this matters even more. Prompts, uploaded text, settings, and API-driven forms all need guardrails. In this post, we’ll build a simple document form in Rails and validate it properly. Generate a resource If you’ve been following along, you already have a Document model. Let’s assume it looks like this: class Document < ApplicationRecord belongs_to :project end And the table has these columns: project_id title body status Now create a controller if you don’t already have one: bin/rails generate controller Documents new create edit update Add routes in config/routes.rb : Rails . application . routes . draw do resources :projects do resources :documents , only: [ :new , :create , :edit , :update ] end end Nested routes make sense here because a document belongs to a project. Add model validations Start with