Optional Fields

Part of the REST APIs section of Coddy's Node.js journey. Lesson 9 of 25.

A complete task needs a title and a done value. A PATCH request may change only one of them. Calling .partial() on an object schema makes its fields optional while keeping the rules for any fields that are present.

const ChangeBook = Book.partial();
ChangeBook.safeParse({year: 2000});

The omitted title is allowed, but a supplied year must still be a number. Partial does not turn incorrect values into valid ones. The original schema remains unchanged, so a route that replaces a complete resource can continue to require every field.

Book.partial({ pages: true }) makes only pages optional; other fields stay required. A creation request often omits a field with a default while still requiring the main title. After parsing, const { pages = 1 } = result.data supplies 1 when the field was omitted.

Challenge

Easy

Edit the two schema assignments in exercise.js. Keep Task as the complete record. Make ChangeTask accept omitted fields for PATCH. Make NewTask require a title but allow done to be omitted.

POST {} to /result: expect {"change":true,"create":false}. A body of {"title":"Read"} passes both. Supplied values still need the right type: {"done":"false"} fails both.

The initial GET /result uses the supplied example {}. Use POST /result with a JSON body to try other inputs.

Try it yourself

import { z } from 'zod';
const Task = z.object({ title: z.string(), done: z.boolean() });
const ChangeTask = Task;
const NewTask = Task;
export function exercise(body) {
    return { change: ChangeTask.safeParse(body).success, create: NewTask.safeParse(body).success };
}