Grind’s Validation provider leverages the popular Joi validation package behind the scenes to provide you an extensive validation suite with a simple and easy to use API that feels right at home in your Grind application.

First, add the grind-validation package via your preferred package manager:

yarn add grind-validation

Next, you’ll need to add ValidationProvider to your app providers in app/Boostrap.js:

import Grind from 'grind-framework'
import { ValidationProvider } from 'grind-validation'
const app = new Grind()

To validate a request, just pass the body to validate, define your rules and you’re good to go:

async store(req, res) {
  await, rule => {
    username: rule.string().min(3).max(10)
  return res.send('Success')

That’s it. If there’s any validation errors, the validator will throw a ValidationError that you can catch for advanced handling, if you‘d like. By default, Validation sets up a custom error handler for ValidationError:

  • For XHR/JSON requests, the error handler will return a 400 status code and an error payload that includes the violations.
  • For other requests, the error handler will flash the errors, flash the current input and redirect back to the original request. If you‘re using FormBuilder, when redirected back to the original page, the forms will already be prefilled with the previous input.

For a comprehensive list of rules you can use, check out the detailed Joi documentation.

For performance purposes, you may want to prebuild the rules ahead of time and then reuse them in each validation call. This is easy to do via the build method:

const rules = => {
  username: rule.string().min(3).max(10)
await, rules)

Grind exposes an easy way to define custom rules via the extend method.

extend(name, type, options, validator)
  • name: This is the name of your rule that you’ll call later when using it.
  • type: (optional) The data type for your rule, valid values are: any, array, boolean, binary, date, number, object and string. If you don’t provide the parameter, it will default to any.
  • options: (optional) The options parameter are raw Joi options you can use to customize if necessary.
  • validator: This is the callback parameter used to validate the value. It’s passed the following parameters:
    • value: The value to validate
    • params: Any parameters passed to your rule
    • context: The current rule object
export function ValidationRulesProvider(app) {
  app.validator.extend('test', 'string', value => {
    if(value !== 'test') {
      throw new Error('invalid test value')
    return value

Once your rule is defined, you can start using it just like any other rule:

await, rule => {
  username: rule.string().min(3).max(10),
  someField: rule.string().test()

Errors are automatically exposed to your Views via messages.errors. Here‘s an example of how to display errors in a simple list:

@if(messages && messages.errors && messages.errors.length > 0)
  <ul class="errors">
    @for(const [ field, errors ] of Object.entries(messages.errors[0]))
      @for(error of errors)
        <li class="error">{{ error.message }}</li>