Custom Model Validation in LoopBack: A Step-by-Step Guide

8 August 2024

LoopBack Custom Model Validation

LoopBack is a powerful Node.js framework that simplifies the process of building RESTful APIs. One of its key features is its robust model validation system. However, sometimes you might need to perform custom validations on your models that are not directly supported by LoopBack’s built-in validation mechanisms.
In this article, we’ll explore how to implement custom model validation in LoopBack. We’ll create a simple example to demonstrate the process, and I’ll provide code snippets to help illustrate each step.

Why Custom Model Validation?

Before we dive into the implementation details, let’s quickly discuss why you might need custom model validation in LoopBack. While LoopBack provides an excellent built-in validation system, there are cases where you might want to perform more complex or application-specific validations on your models.
For instance, imagine a scenario where you’re building an e-commerce API that requires validating the shipping address of an order. You might want to validate that the shipping address is within a certain distance from the customer’s location or that it meets specific criteria (e.g., zip code, city). These are scenarios where custom model validation comes in handy.

Implementing Custom Model Validation

To implement custom model validation in LoopBack, you’ll need to follow these steps:

1. Create a custom validator class

Create a new JavaScript file for your custom validator class and export it as a module. In this example, we’ll create a file called distanceValidator.js.

// distanceValidator.js
const distance = (address) => {
  // calculate the distance from the address to the customer's location
  return Math.sqrt(Math.pow(address.longitude - customerLocation.longitude, 2) + Math.pow(address.latitude - customerLocation.latitude, 2));
};
module.exports = distance;

2. Define a custom validation rule

In your LoopBack model definition file, add a new validation rule using the validate method.

// models/user.js
const User = Model.extend('user', {
  // other properties and methods...
  validate: ['distance'],
});
User.validatesPresenceOf('shippingAddress');

3. Use the custom validator in your model

In this example, we’re using a custom validator called distance to ensure that the shipping address is within a certain distance from the customer’s location.

// models/user.js (continued)
const validate = require('./distanceValidator');
User.remoteMethod('validateShippingAddress', {
  http: { path: '/validateShippingAddress', verb: 'post' },
  accepts: [{ arg: 'shippingAddress', type: 'object' }],
  returns: [{ arg: 'boolean', type: 'boolean' }],
});
User.validateShippingAddress = function(shippingAddress, cb) {
  const distanceFromCustomerLocation = validate(this.shippingAddress);
  if (distanceFromCustomerLocation > MAX_DISTANCE) {
    return cb(false, 'Shipping address is too far from customer location');
  }
  return cb(null, true);
};

And that’s it! By following these steps and implementing custom model validation in LoopBack, you can ensure that your API has robust validation rules for complex scenarios.

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