Filtering Lists

Part of the REST APIs section of Coddy's Node.js journey. Lesson 14 of 25.

A client that wants only the open tasks should not download every task and throw most away. The query string, the part after ?, narrows the list on the server:

// GET /api/invoices?paid=false
const { paid } = req.query;
let list = invoices;
if (paid !== undefined) {
    list = list.filter((i) => i.paid === (paid === 'true'));
}

Query values are always strings. req.query.paid is 'false', and a string that is not empty is truthy, so if (paid) treats ?paid=false like ?paid=true. Compare with the string instead, and answer 400 for a value that is neither 'true' nor 'false'. Each filter narrows what the one before it left, so several filters combine.

Challenge

Easy

A client that wants only the open tasks should not download all of them. Let the list filter itself with the query string.

In routes/tasks.js, in the list route (GET /api/tasks), read done and q from req.query. With neither, the route still returns every task.
?done=true returns only finished tasks, and ?done=false only open ones. The value arrives as the text "true" or "false", not a boolean. Any other value, like ?done=yes, gets status 400:
```
{ "error": { "code": "invalid_query", "message": "done must be true or false" } }
```
?q=room returns only tasks whose title contains room, ignoring case, so it also finds "Pay the ROOM deposit".
Both filters can be used at once: ?done=false&q=room returns open tasks with room in the title.

Try it: GET /api/tasks?done=false returns tasks 2 and 3. GET /api/tasks?q=room returns only task 2, "Book the meeting room". GET /api/tasks?done=true&q=room returns an empty list, []. GET /api/tasks?done=yes returns 400 with code invalid_query.

Try it yourself

import { Router } from 'express';
import { z } from 'zod';
import { sendError, sendInvalid } from '../errors.js';
import { nextId, tasks } from '../store.js';

const router = Router();

// A whole task, as PUT sends it. .strict() refuses fields it does not list.
const Task = z
    .object({
        title: z.string().trim().min(1).max(100),
        done: z.boolean(),
    })
    .strict();
const NewTask = Task.partial({ done: true });
const TaskChanges = Task.partial();

// True when another task already has this title, in any case.
const titleTaken = (title, exceptId) =>
    tasks.some((t) => t.id !== exceptId && t.title.toLowerCase() === title.toLowerCase());

router.get('/', (req, res) => {
    res.json(tasks);
});

router.get('/:id', (req, res) => {
    const task = tasks.find((t) => t.id === Number(req.params.id));
    if (!task) {
        return sendError(res, 404, 'not_found', 'Task not found');
    }
    res.json(task);
});

router.post('/', (req, res) => {
    const result = NewTask.safeParse(req.body);
    if (!result.success) {
        return sendInvalid(res, result.error);
    }
    const { title, done = false } = result.data;
    if (titleTaken(title)) {
        return sendError(res, 409, 'conflict', 'A task with this title already exists');
    }
    const task = { id: nextId(), title, done, createdAt: new Date().toISOString() };
    tasks.push(task);
    res.status(201).location(`/api/tasks/${task.id}`).json(task);
});

router.patch('/:id', (req, res) => {
    const task = tasks.find((t) => t.id === Number(req.params.id));
    if (!task) {
        return sendError(res, 404, 'not_found', 'Task not found');
    }
    const result = TaskChanges.safeParse(req.body);
    if (!result.success) {
        return sendInvalid(res, result.error);
    }
    if (result.data.title !== undefined && titleTaken(result.data.title, task.id)) {
        return sendError(res, 409, 'conflict', 'A task with this title already exists');
    }
    Object.assign(task, result.data);
    res.json(task);
});

router.put('/:id', (req, res) => {
    const index = tasks.findIndex((t) => t.id === Number(req.params.id));
    if (index === -1) {
        return sendError(res, 404, 'not_found', 'Task not found');
    }
    const result = Task.safeParse(req.body);
    if (!result.success) {
        return sendInvalid(res, result.error);
    }
    const { id, createdAt } = tasks[index];
    if (titleTaken(result.data.title, id)) {
        return sendError(res, 409, 'conflict', 'A task with this title already exists');
    }
    tasks[index] = { id, ...result.data, createdAt };
    res.json(tasks[index]);
});

router.delete('/:id', (req, res) => {
    const index = tasks.findIndex((t) => t.id === Number(req.params.id));
    if (index === -1) {
        return sendError(res, 404, 'not_found', 'Task not found');
    }
    tasks.splice(index, 1);
    res.status(204).end();
});

export default router;