Implementing Custom Validation Rules in Aurelia

Aurelia is a powerful and flexible JavaScript framework that provides a robust validation system. In this article, we will explore how to implement custom validation rules in Aurelia using the Aurelia Validation plugin.

What is Aurelia Validation?

Aurelia Validation is a plugin that provides a simple and intuitive way to validate forms and data in Aurelia applications. It allows you to define validation rules for your models and then validate them against those rules.

Creating a Custom Validation Rule

To create a custom validation rule in Aurelia, you need to create a class that implements the ValidationRule interface. This interface requires you to implement two methods: match and message.

import { ValidationRule } from 'aurelia-validation';

class CustomValidationRule implements ValidationRule {
  match(value: any, model: any): boolean {
    // Implement your custom validation logic here
    return true;
  }

  message(): string {
    // Return the error message for this validation rule
    return 'Custom validation error';
  }
}

Registering the Custom Validation Rule

Once you have created your custom validation rule, you need to register it with the Aurelia Validation plugin. You can do this by calling the register method on the ValidationProvider instance.

import { ValidationProvider } from 'aurelia-validation';

const provider = new ValidationProvider();
provider.register(new CustomValidationRule());

Using the Custom Validation Rule

Once you have registered your custom validation rule, you can use it to validate your models. You can do this by calling the validate method on the ValidationProvider instance and passing in your model and the custom validation rule.

import { ValidationProvider } from 'aurelia-validation';

const provider = new ValidationProvider();
const model = new MyModel();
const result = provider.validate(model, new CustomValidationRule());

if (result.valid) {
  console.log('Model is valid');
} else {
  console.log('Model is not valid');
}

Example Use Case

Let's say you have a model that represents a user, and you want to validate that the user's email address is valid. You can create a custom validation rule that checks if the email address is valid, and then use that rule to validate your model.

class User {
  email: string;
}

class EmailValidationRule implements ValidationRule {
  match(value: string, model: User): boolean {
    const emailRegex = /^[a-zA-Z0-9._%+@[a-zA-Z0-9.-]+\.[a-zA-Z0-9]{2,}$];
    return emailRegex.test(value);
  }

  message(): string {
    return 'Invalid email address';
  }
}

const provider = new ValidationProvider();
const user = new User();
user.email = 'invalid email';

const result = provider.validate(user, new EmailValidationRule());

if (result.valid) {
  console.log('Email is valid');
} else {
  console.log('Email is not valid');
}

Conclusion

In this article, we have seen how to implement custom validation rules in Aurelia using the Aurelia Validation plugin. We have created a custom validation rule that checks if a user's email address is valid, and then used that rule to validate our model. This is just one example of how you can use custom validation rules in Aurelia to validate your models.

FAQs

Here are some frequently asked questions about implementing custom validation rules in Aurelia:

1. What is the purpose of the match method in a custom validation rule?

   The match method is used to determine whether the value being validated matches the validation rule. It should return true if the value is valid, and false otherwise.

2. What is the purpose of the message method in a custom validation rule?

   The message method is used to return the error message for the validation rule. This message will be displayed to the user if the validation rule is not met.

3. How do I register a custom validation rule with the Aurelia Validation plugin?

   You can register a custom validation rule by calling the register method on the ValidationProvider instance and passing in the custom validation rule.

4. How do I use a custom validation rule to validate a model?

   You can use a custom validation rule to validate a model by calling the validate method on the ValidationProvider instance and passing in the model and the custom validation rule.

5. Can I use multiple custom validation rules to validate a model?

   Yes, you can use multiple custom validation rules to validate a model. You can pass an array of custom validation rules to the validate method.