Fluent Validation Builder for TypeScript 💡

Elegant and type-safe model validation made easy.

Overview 🌐

Tired of unreadable and messy model validation logic? Meet valid-fluent Builder! Leverage the power of TypeScript and clean code principles to write clear, expressive, and type-safe validation rules for your application models.

Features 🌟

• Fluent API design for easy readability
• Full TypeScript support for strong type safety
• Flexible and extensible
• Supports conditional validation
• Supports synchronous and asynchronous validation
• Optional "fail fast" mode to stop validation on first error
• In-built type-checking methods for common types (Number, String, Boolean, Date, and more)

Installation 📦

npm install valid-fluent

Basic Usage 🚀

Import the main ValidationBuilder class and start building your validation logic.

import { ValidationBuilder } from 'valid-fluent';

const validation = ValidationBuilder.create<User>()
  .forField('username', u => u.username)
  .addRule(({value}) => value !== '')
  .withMessage('Username is required')
  .build();

const result = validation.validate(user);

Type-Checking and Type-Specific Methods

Valid-Fluent now incorporates handy methods for validating common data types. Additionally, when you specify a data type using isNumber, isString, isBoolean, or isDate, you unlock type-specific validation methods for that field. Here's how to use them:

const validation = ValidationBuilder.create<User>()
    
.forField('age', u => u.age)
    .isNumber()
    .withMessage('Must be number')
    .isGreaterThan(18)
    .withMessage('You must be over 18')
.forField('email', u => u.email)
    .isString()
    .withMessage('Must be string')
    .matches(/@/)
    .withMessage('Email must contain "@"')
.forField('isActive', u => u.isActive)
    .isBoolean()
    .withMessage('Must be boolean')
    .isTrue()
    .withMessage('You must be active')
.build();

These methods not only ensure the correct data type but also provide a fluent and expressive way to define further validation rules based on the data type.

Async Validation

Asynchronous validators can be added just like regular validators. They should return a Promise.

const asyncValidation = ValidationBuilder.create<User>()
  .forField('username', u => u.username)
  .addRule(async ({value}) => {
    const userExists = await checkUserExists(value);
    return !userExists;
  })
  .withMessage('Username already exists')
  .build();

const asyncResult = await asyncValidation.validateAsync(user);

Core Concepts

The entry point for creating validations. Start by calling

ValidationBuilder.create<ModelType>()

Use .forField() method to specify the property you want to validate.

builder.forField('email', u => u.email)

Once you've added a rule, you can attach an error message using .withMessage().

builder.addRule(emailValidator)
.withMessage('Invalid email!')

You can also pass a function to withMessage to dynamically generate error messages based on the model's current state.

builder.forField('age', u => u.age)
.addRule(({ value }) => value >= 18)
.withMessage(model => `Must be at least 18 years old, but got ${model.age}.`);

In the dynamic error message example above, if the age field validation fails, the error message will reflect the actual age value from the model, providing a more descriptive error message.

Conditional Rules

Conditional rules enable dynamic validations. Use .when() to conditionally apply a validation rule.

builder.addRule(emailValidator)
.when(model => model.subscribeToNewsletter)

You can also add a condition to multiple validation rules by using the builder callback provided by when:

builder.when(model => model.subscribeToNewsletter, builder =>
  builder
      .forField('email', u => u.email)
        .addRule(emailValidator)
        .withMessage('Invalid email!')
      .forField('age', u => u.age)
        .addRule(ageValidator)
        .withMesasge('You are not old enough'));

Dependent Field Validation

To include a dependent field in validation, use the .dependsOn() method.

builder.forField('passwordConfirmation', u => u.passwordConfirmation)
.dependsOn(u => u.password)

Custom Validators

You can create custom validation rules by passing your own validator functions to .addRule().

const emailValidator = args => {
  const { value } = args;

  return value.includes('@');
};

builder.addRule(emailValidator)

You could also do this inline:

builder
    .forField('email', model => model.email)
    .addRule(args => {
      const { value } = args;
    
      return value.includes('@')
})

You can use the ValidatorArgs-type to type your validator.

Handling Validation Outcomes 🔍

Once you've defined your validation rules and run the validation, you'll receive a ValidationOutcome object. This object will be of type ValidationSuccess if the validation passes, or ValidationError if it fails. Here's how you can use this object to inspect any validation errors:

const outcome = validation.validate(user);

if (!outcome.isValid) {
    // Validation failed
    const passwordError = outcome.result.password;
    console.error(`${passwordError.propertyName}: ${passwordError.message}`);
    // Output: password: Password must match username for some reason
}

In the ValidationError object, the result field contains a ValidationResult object where each key is the name of a field in your model, and the value is an object containing the field's name and the validation error message.

Here's a more structured example using a test suite:

test('should validate password', () => {
    const outcome = validation.validate(user);
    
    if (!outcome.isValid) {
        expect(outcome.result.password.propertyName).toBe('password');
        expect(outcome.result.password.message).toBe('Password must match username for some reason');
    }
});

This structure allows you to easily access validation error messages and the corresponding field names, making error handling and reporting straightforward and type-safe.

Upcoming Features

• [x] Async Validators
• [ ] Validation Result Transformation
• [ ] Custom Validation Error Handling
• [ ] Validation Groups
• [ ] Integration with Popular Libraries/Frameworks

Contributing 🤝

Feel free to contribute by opening issues, sending pull requests, or just by sharing your thoughts on making this package better.

License 📜

MIT License.