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Backend methods

When performing operations on multiple entity objects, performance considerations may necessitate running them on the server. With Remult, moving client-side logic to run on the server is a simple refactoring.

Set All Tasks as Un/complete

Let's add two buttons to the todo app: "Set all as completed" and "Set all as uncompleted".

  1. Add a setAllCompleted async function to +page.svelte function component, which accepts a completed boolean argument and sets the value of the completed field of all the tasks accordingly.
<script lang="ts">
  async function setAllCompleted(completed: boolean) {
    for (const task of await taskRepo.find()) {
      await{ ...task, completed })

The for loop iterates the array of Task objects returned from the backend, and saves each task back to the backend with a modified value in the completed field.

  1. Add the two buttons to the end of the </main> section of the markup. Both of the buttons' on:click events will call the setAllCompleted function with the appropriate value of the completed argument.

  <button on:click={() => setAllCompleted(true)}>Mark All Completed</button>
  <button on:click={() => setAllCompleted(false)}>Mark All Incomplete</button>

Make sure the buttons are working as expected before moving on to the next step.

Refactor from Front-end to Back-end

With the current state of the setAllCompleted function, each modified task being saved pushes a PUT request handled separately by the server. As the number of tasks in the todo list grows, this may become a performance issue. You can verify this on the Network tab of your browser's Developer Tools.

A simple way to prevent this is to expose an API endpoint for setAllCompleted requests, and run the same logic on the server instead of the client.

  1. Create a new TasksController class, in the shared folder, and refactor into a new, static, setAllCompleted method in the TasksController class, which will run on the server.
import { BackendMethod, remult } from 'remult'
import { Task } from './Task'

export class TasksController {
  @BackendMethod({ allowed: true })
  static async setAllCompleted(completed: boolean) {
    const taskRepo = remult.repo(Task)

    for (const task of await taskRepo.find()) {
      await taskRepo.update(, { completed })

The @BackendMethod decorator tells Remult to expose the method as an API endpoint (/api/setAllCompleted) and allow CRUD operations on this end-point ({allowed: true} - more details to follow).

Unlike the front-end Remult object, the server implementation interacts directly with the database.

  1. Register the new TasksController class by adding it to the controllers array of the options object passed to remultSveltekit(), in the server's hooks.server.ts file:
import { remultSveltekit } from 'remult/remult-sveltekit'
import { Task } from './shared/Task'
import { TasksController } from './shared/TasksController'

export const handle = remultSveltekit({
  entities: [Task],
  controllers: [TasksController],

3.Replace the for iteration in the setAllCompleted function of with a call to the setAllCompleted method in the TasksController.

const setAllCompleted = async (completed: boolean) => {
  /* for (const task of await taskRepo.find()) {
    await{ ...task, completed });
  } */
  await TasksController.setAllCompleted(completed) 

Import TasksController

Remember to add an import of TasksController in +page.svelte.


With Remult backend methods, argument types are compile-time checked. 👍


You might need vite-plugin-stripper as a devDependency to build your application for production.

After the browser is refreshed, the "Set all..." buttons function exactly the same but now makes only a single request to the back, and is faster.

MIT Licensed | Made by the Remult team with ❤️