Custom Validations in Rails

When working with Ruby on Rails, validations are an essential part of ensuring that the data in your application is accurate and consistent. While Rails provides a set of built-in validation helpers, there may be cases where you need to create custom validations to meet the specific requirements of your application. In this article, we will explore how to implement custom validations in Rails.

Creating Custom Validations

Custom validations in Rails are implemented by creating a custom validator class that inherits from ActiveModel::Validator. This class should define a validate method that takes the record being validated as an argument. Inside the validate method, you can add your custom validation logic.

class CustomValidator < ActiveModel::Validator
  def validate(record)
    unless record.name.start_with?('A')
      record.errors.add :name, 'must start with the letter A'
    end
  end
end

Once you have defined your custom validator class, you can use it in your model by calling validates_with and passing in the name of your custom validator class.

class User < ApplicationRecord
  validates_with CustomValidator
end

Using Custom Validations

Custom validations can be used in the same way as built-in validations in Rails. When you save a record that fails a custom validation, the errors will be added to the record's errors collection, just like with built-in validations.

For example, if we try to save a User record with a name that does not start with the letter 'A', the validation will fail and an error message will be added to the name attribute.

user = User.new(name: 'John')
user.save
puts user.errors.full_messages
# => ["Name must start with the letter A"]

Common Use Cases for Custom Validations

There are many scenarios where custom validations can be useful in a Rails application. Some common use cases include:

Validating complex business rules that cannot be expressed with built-in validations
Performing cross-field validations that involve multiple attributes
Validating against external services or APIs

By creating custom validations, you can ensure that your application enforces the specific business rules and requirements that are unique to your domain.

Conclusion

Custom validations in Rails provide a powerful way to enforce data integrity and ensure that your application meets the specific requirements of your domain. By creating custom validator classes and using them in your models, you can add complex validation logic that goes beyond the built-in validation helpers provided by Rails. Whether you need to validate against external services, enforce complex business rules, or perform cross-field validations, custom validations give you the flexibility to tailor the validation logic to the needs of your application.