Had the same problem before and its very painful especially if its a deep array or array of objects to validate. I ended up creating my own validator (wallter) that will handle this issue. And also this tool can generate validation schema straight from your mongoose model.

So your schema above will generate a validation schema:

{
  "name": {
    "required": {
      "msg": "Value for field 'name' is required"
    }
  },
  "description": {
    "optional": true
  },
  "items.*.name": {
    "required": {
      "msg": "Value for field 'items.*.name' is required"
    }
  },
  "items.*.rate": {
    "required": {
      "msg": "Value for field 'items.*.rate' is required"
    },
    "isDecimal": {
      "msg": "Expecting 'decimal' value for field 'items.*.rate'"
    }
  },
  "items.*.quantity": {
    "required": {
      "msg": "Value for field 'items.*.quantity' is required"
    },
    "isDecimal": {
      "msg": "Expecting 'decimal' value for field 'items.*.quantity'"
    }
  },
  "items.*.amount": {
    "optional": true,
    "isDecimal": {
      "msg": "Expecting 'decimal' value for field 'items.*.amount'"
    }
  }
}

This validation schema can be fed to validator

const halter = require('wallter').halter
const Builder = require('wallter').builder // validation schema builder

const builder = new Builder({
  model: mongoose.model('YourModelName')
})

server.use(halter())

server.post('/test', function (req, res, next) {
    let validationSchema = builder.build() // see above generated validation schema output

    req.halt(validationSchema).then(result => {
        if (result.length) {
            res.send(400, result)
        } else {
            res.send(200)
        }

        return next()
    })
})