How to validate an array of objects in a request body using JOI

I am trying to validate the request body of an order placed. I recieve an array of json objects on the request body that I am trying to validate. Everytime I get the error " "productId" is required"

Here is my request body:

req.body={
    "productId": [
        { "id": "5dd635c5618d29001747c01e", "quantity": 1 },
        { "id": "5dd63922618d29001747c028", "quantity": 2 },
        { "id": "5dd635c5618d29001747c01e", "quantity": 3 }
    ]
}

Here is the valdateOrder function to validate the request body:

function validateOrder(req.body) {
    const schema = {

        productId: joi.array().items(
            joi.object().keys({
                id: joi.string().required(),
                quantity: joi.string().required()
            })).required(),
    }

    return joi.validate(req.body, schema)

}

I would be really thankful if anyone can point out whats wrong with my validateOrder function.

This seems an odd way to go about it. As per https://hapi.dev/module/joi/, define your schema as its own thing, then validate your data using that schema:

const Joi = require('@hapi/joi');

const schema = Joi.object({
  productId: Joi.array().items(
    Joi.object(
      id: Joi.string().required(),
      quantity: Joi.number().required()
    )
  )
};

module.exports = schema;

And then you validate with that in your route middleware:

const Joi = require('@hapi/joi');
const schema = require(`./your/schema.js`);

function validateBody(req, res, next) {
  // If validation passes, this is effectively `next()` and will call
  // the next middleware function in your middleware chain.

  // If it does not, this is efectively `next(some error object)`, and
  // ends up calling your error handling middleware instead. If you have any.

  next(schema.validate(req.body));
}

module.exports = validateBody;

Which you use like any other middleware in express:

const validateBody = require(`./your/validate-body.js`);

// general error handler (typically in a different file)
function errorHandler(err, req, res, next) {
  if (err === an error you know comes form Joi) {
    // figure out what the best way to signal "your POST was bad"
    // is for your users
    res.status(400).send(...);
  }
  else if (...) {
    // ...
  }
  else {
    res.status(500).send(`error`);
  }
});

// and then tell Express about that handler
app.use(errorHandler);

// and then you inclide your body validator in your
// post handling middleware chain:
app.post(
  `route`,
  ...,
  validateBody,
  ...,
  (req, res) => res.json(...)
);