Designing a CRUD interface

An excellent use case for Superforms is a backend interface, commonly used as in the acronym CRUD (Create, Read, Update, Delete):

Display an empty form
POST the form, validate the data
Create a new entity with the data (Create)
Fetch the entity (Read)
Display it in a form
POST the form, validate the data
Update the entity with the data (Update)
Delete the entity (Delete)
???
Profit!

Because you can send the data model to the superValidate function and have the form directly populated, it becomes quite easy to implement the above steps.

Getting started

To follow along, there are three ways:

Video tutorial

Instead of the text version below, here’s the video version. It’s using version 1 of Superforms, but the differences are small; use an adapter and add resetForm: false to the options.

Stackblitz

The code is available on Stackblitz. Just click the link, and you’re up and running in the browser in less than 30 seconds!

New SvelteKit project

Start from scratch in a new SvelteKit project by executing one of the following commands in your project directory:

npm create svelte@latest

pnpm create svelte@latest

Select Skeleton project and Typescript syntax at the prompts, the rest is up to you. Then add this to <head> in src/app.html for a much nicer visual experience:

<link rel="stylesheet" href="https://unpkg.com/[email protected]/normalize.css" />
<link rel="stylesheet" href="https://unpkg.com/sakura.css/css/sakura.css" />

Start - Creating a test database

When you have the code up and running, we need a user schema, and a mock database for testing. We will use Zod as a validation library, but its schema can easily be converted to others.

src/lib/users.ts

import { z } from 'zod';

// See https://zod.dev/?id=primitives for schema syntax
export const userSchema = z.object({
  id: z.string().regex(/^\d+$/),
  name: z.string().min(2),
  email: z.string().email()
});

type UserDB = z.infer<typeof userSchema>[];

// Let's worry about id collisions later
export const userId = () => String(Math.random()).slice(2);

// A simple user "database"
export const users: UserDB = [
  {
    id: userId(),
    name: 'Important Customer',
    email: '[email protected]'
  },
  {
    id: userId(),
    name: 'Super Customer',
    email: '[email protected]'
  }
];

Form vs. database schemas

When starting on the server page, we’ll encounter a thing about validation schemas. Our userSchema is for database integrity, so an id must exist there. But we want to create an entity, and must therefore allow id not to exist when creating users.

Fortunately, Zod makes it quite easy to append a modifier to a field without duplicating the whole schema by extending it:

src/routes/users/[[id]]/+page.server.ts

import { userSchema } from '$lib/users';

const crudSchema = userSchema.extend({
  id: userSchema.shape.id.optional()
});

(Of course, the original userSchema is kept intact.)

With this, Create and Update can now use the same schema, which means that they can share the same user interface. This is a fundamental idea in Superforms: you can pass either empty data or an entity partially matching the schema to superValidate, and it will generate default values for any non-specified fields, ensuring type safety.

Reading a user from the database

Let’s add a load function to the page, using the SvelteKit route parameters to look up the requested user:

src/routes/users/[[id]]/+page.server.ts

import { superValidate, message } from 'sveltekit-superforms';
import { zod } from 'sveltekit-superforms/adapters';
import { error, fail, redirect } from '@sveltejs/kit';
import { users, userId } from '$lib/users';

export const load = async ({ url, params }) => {
  // READ user
  const user = users.find((u) => u.id == params.id);

  if (params.id && !user) throw error(404, 'User not found.');

  // If user is null, default values for the schema will be returned.
  const form = await superValidate(user, zod(crudSchema));
  return { form, users };
};

Some simple logic is used to find the user, and then detect if a 404 should be displayed. At the end, we’re returning form as usual, but also users, so they can be displayed as a list.

(Sometimes, CRUDL is used as an acronym, since listing is also fundamental to data management.)

Now that we have loaded the data, let’s display it in a page component:

src/routes/users/[[id]]/+page.svelte

<script lang="ts">
  import { page } from '$app/stores';
  import { superForm } from 'sveltekit-superforms';

  let { data } = $props();

  const { form, errors, constraints, enhance, delayed, message } = superForm(
    data.form, {
      resetForm: false
    }
  );
</script>

{#if $message}
  <h3 class:invalid={$page.status >= 400}>{$message}</h3>
{/if}

<h2>{!$form.id ? 'Create' : 'Update'} user</h2>

There are plenty of variables extracted from superForm; refer to the API reference for a complete list. We’ve also setting the resetForm to false, since the data should be kept after editing.

We’ve also prepared a status message, using $page.status to test for success or failure, and we’re using $form.id to display a “Create user” or “Update user” title. Now let’s add the form itself:

src/routes/users/[[id]]/+page.svelte (continued)

<form method="POST" use:enhance>
  <input type="hidden" name="id" bind:value={$form.id} />

  <label>
    Name<br />
    <input
      name="name"
      aria-invalid={$errors.name ? 'true' : undefined}
      bind:value={$form.name}
      {...$constraints.name} />
    {#if $errors.name}<span class="invalid">{$errors.name}</span>{/if}
  </label>

  <label>
    E-mail<br />
    <input
      name="email"
      type="email"
      aria-invalid={$errors.email ? 'true' : undefined}
      bind:value={$form.email}
      {...$constraints.email} />
    {#if $errors.email}<span class="invalid">{$errors.email}</span>{/if}
  </label>

  <button>Submit</button> {#if $delayed}Working...{/if}
</form>

<style>
  .invalid {
    color: red;
  }
</style>

Remember to use SuperDebug if you want to see your form data live!

<script>
  import SuperDebug from 'sveltekit-superforms';
</script>

<SuperDebug data={$form} />

Creating and Updating a user

With this, the form should be ready for creating a user. Let’s add the form action for that:

src/routes/users/[[id]]/+page.server.ts

export const actions = {
  default: async ({ request }) => {
    const form = await superValidate(request, zod(crudSchema));
    if (!form.valid) return fail(400, { form });

    if (!form.data.id) {
      // CREATE user
      const user = { ...form.data, id: userId() };
      users.push(user);

      return message(form, 'User created!');
    } else {
      // UPDATE user
      const index = users.findIndex((u) => u.id == form.data.id);
      if (index == -1) throw error(404, 'User not found.');

      users[index] = { ...form.data, id: form.data.id };
      return message(form, 'User updated!');
    }

    return { form };
  }
};

This is where you should access your database API. In our case, we’re only doing some array manipulations.

With this, we have 3 out of 4 letters of CRUD in about 150 lines of code, half of it HTML!

Deleting a user

To delete a user, we can make use of the HTML button element, which can have a name and a value that will be passed only if that specific button was used to post the form. Add this at the end of the form:

src/routes/users/[[id]]/+page.svelte

{#if $form.id}
  <button
    name="delete"
    on:click={(e) => !confirm('Are you sure?') && e.preventDefault()}
    class="danger">Delete user</button>
{/if}

In the form action, we now use the FormData from the request to check if the delete button was pressed.

We can also add a delayed button in the form to mimick the behavior of a slow network call:

<button name="delay" class="delay">Submit delayed</button>

We shouldn’t use the schema since delete and delayed are not a part of the user, but it’s not a big change:

src/routes/users/[[id]]/+page.server.ts

export const actions: Actions = {
  default: async ({ request }) => {
    const formData = await request.formData();
    const form = await superValidate(formData, zod(crudSchema));

    if (formData.has('delay')) {
      await new Promise((r) => setTimeout(r, 2000));
    }

    if (!form.valid) return fail(400, { form });

    if (!form.data.id) {
      // CREATE user
      const user = { ...form.data, id: userId() };
      users.push(user);

      return message(form, 'User created!');
    } else {
      const index = users.findIndex((u) => u.id == form.data.id);
      if (index == -1) throw error(404, 'User not found.');

      if (formData.has('delete')) {
        // DELETE user
        users.splice(index, 1);
        throw redirect(303, '/users');
      } else {
        // UPDATE user
        users[index] = { ...form.data, id: form.data.id };
        return message(form, 'User updated!');
      }
    }
  }
};

Now all four CRUD operations are complete! An issue, however, is that we have to redirect after deleting to avoid a 404, so we cannot use form.message to show “User deleted”, since the validation data won’t exist after redirecting.

Redirecting with a message is a general problem; for example, maybe we’d like to redirect to the newly created user after it’s been created. Fortunately, there is a solution; the sister library to Superforms handles this. Read more about it here.

Listing the users

The last loose thread is to display a list of the users. It’ll be quite trivial; add this to the top of +page.svelte:

src/routes/+page.svelte

<h3>Users</h3>
<div class="users">
  {#each data.users as user}
    <a href="/users/{user.id}">{user.name}</a>
  {/each}
</div>

And some styling for everything at the end:

<style>
  .invalid {
    color: red;
  }

  .danger {
    background-color: brown;
  }

  .delay {
    background-color: lightblue;
  }

  form {
    display: flex;
    flex-direction: column;
    gap: 1em;
    align-items: flex-start;
    margin-bottom: 2em;
  }

  hr {
    width: 100%;
    margin-block: 2em;
  }

  .users {
    columns: 3 150px;
  }

  .users > * {
    display: block;
    white-space: nowrap;
    overflow-x: hidden;
  }
</style>

That’s it! Thank you for following along, the code is available here on Stackblitz.

If you have any questions, see the help & support page.