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/completed

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 the App function component, which accepts a completed boolean argument and sets the value of the completed field of all the tasks accordingly.

   // src/App.tsx
   
   const setAllCompleted = async (completed: boolean) => {
     for (const task of await taskRepo.find()) {
       await taskRepo.save({ ...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.

2. Add the two buttons to the return section of the App component, just before the closing </main> tag. Both of the buttons' onClick events will call the setAllCompleted method with the appropriate value of the completed argument.

   // src/App.tsx
   
   <div>
     <button onClick={() => setAllCompleted(true)}>Set All Completed</button>
     <button onClick={() => setAllCompleted(false)}>Set All Uncompleted</button>
   </div>

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 causes an API PUT request handled separately by the server. As the number of tasks in the todo list grows, this may become a performance issue.

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 the for loop from the setAllCompleted function of the App function component into a new, static, setAllCompleted method in the TasksController class, which will run on the server.

// src/shared/TasksController.ts

import { BackendMethod, remult } from 'remult'
import { Task } from './Task.js'

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.save({ ...task, completed })
    }
  }
}

The @BackendMethod decorator tells Remult to expose the method as an API endpoint (the allowed property will be discussed later on in this tutorial).

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

2. Register TasksController by adding it to the controllers array of the options object passed to remultExpress(), in the server's api module:

// src/server/api.ts

//...
import { TasksController } from "../shared/TasksController.js"

export const api = remultExpress({
  //...
  controllers: [TasksController]
})

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

// src/App.tsx

const setAllCompleted = async (completed: boolean) => {
  await TasksController.setAllCompleted(completed)
}

Import TasksController

Remember to add an import of TasksController in App.tsx.

Note

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

After the browser refreshed, the "Set all..." buttons function exactly the same, but much faster.