Agent Skills: Inertia Rails Forms

Inertia Rails Forms

Comprehensive guide to building forms in Inertia Rails applications with React, Vue, or Svelte.

The useForm Helper

The useForm helper provides reactive form state management with built-in features for validation, file uploads, and submission handling.

React

import { useForm } from '@inertiajs/react'

export default function CreateUser() {
  const { data, setData, post, processing, errors, reset } = useForm({
    name: '',
    email: '',
    password: '',
    avatar: null,
  })

  function submit(e) {
    e.preventDefault()
    post('/users', {
      onSuccess: () => reset('password'),
      preserveScroll: true,
    })
  }

  return (
    <form onSubmit={submit}>
      <div>
        <label>Name</label>
        <input
          type="text"
          value={data.name}
          onChange={(e) => setData('name', e.target.value)}
        />
        {errors.name && <span className="error">{errors.name}</span>}
      </div>

      <div>
        <label>Email</label>
        <input
          type="email"
          value={data.email}
          onChange={(e) => setData('email', e.target.value)}
        />
        {errors.email && <span className="error">{errors.email}</span>}
      </div>

      <div>
        <label>Password</label>
        <input
          type="password"
          value={data.password}
          onChange={(e) => setData('password', e.target.value)}
        />
        {errors.password && <span className="error">{errors.password}</span>}
      </div>

      <div>
        <label>Avatar</label>
        <input
          type="file"
          onChange={(e) => setData('avatar', e.target.files[0])}
        />
      </div>

      <button type="submit" disabled={processing}>
        {processing ? 'Creating...' : 'Create User'}
      </button>
    </form>
  )
}

Vue 3

<script setup>
import { useForm } from '@inertiajs/vue3'

const form = useForm({
  name: '',
  email: '',
  password: '',
  avatar: null,
})

function submit() {
  form.post('/users', {
    onSuccess: () => form.reset('password'),
    preserveScroll: true,
  })
}
</script>

<template>
  <form @submit.prevent="submit">
    <div>
      <label>Name</label>
      <input v-model="form.name" type="text" />
      <span v-if="form.errors.name" class="error">{{ form.errors.name }}</span>
    </div>

    <div>
      <label>Email</label>
      <input v-model="form.email" type="email" />
      <span v-if="form.errors.email" class="error">{{ form.errors.email }}</span>
    </div>

    <div>
      <label>Password</label>
      <input v-model="form.password" type="password" />
      <span v-if="form.errors.password" class="error">{{ form.errors.password }}</span>
    </div>

    <div>
      <label>Avatar</label>
      <input type="file" @change="form.avatar = $event.target.files[0]" />
      <progress v-if="form.progress" :value="form.progress.percentage" max="100" />
    </div>

    <button type="submit" :disabled="form.processing">
      {{ form.processing ? 'Creating...' : 'Create User' }}
    </button>
  </form>
</template>

Svelte

<script>
import { useForm } from '@inertiajs/svelte'

const form = useForm({
  name: '',
  email: '',
  password: '',
  avatar: null,
})

function submit() {
  form.post('/users', {
    onSuccess: () => form.reset('password'),
    preserveScroll: true,
  })
}
</script>

<form onsubmit={(e) => { e.preventDefault(); submit() }}>
  <div>
    <label>Name</label>
    <input type="text" bind:value={form.name} />
    {#if form.errors.name}
      <span class="error">{form.errors.name}</span>
    {/if}
  </div>

  <div>
    <label>Email</label>
    <input type="email" bind:value={form.email} />
    {#if form.errors.email}
      <span class="error">{form.errors.email}</span>
    {/if}
  </div>

  <div>
    <label>Password</label>
    <input type="password" bind:value={form.password} />
  </div>

  <div>
    <label>Avatar</label>
    <input type="file" onchange={(e) => (form.avatar = e.target.files[0])} />
  </div>

  <button type="submit" disabled={form.processing}>
    {form.processing ? 'Creating...' : 'Create User'}
  </button>
</form>

Rails Controller Pattern

The standard pattern for handling form submissions:

class UsersController < ApplicationController
  def new
    render inertia: {}
  end

  def create
    user = User.new(user_params)

    if user.save
      redirect_to users_url, notice: 'User created successfully!'
    else
      redirect_to new_user_url, inertia: { errors: user.errors }
    end
  end

  def edit
    user = User.find(params[:id])
    render inertia: { user: user.as_json(only: [:id, :name, :email]) }
  end

  def update
    user = User.find(params[:id])

    if user.update(user_params)
      redirect_to user_url(user), notice: 'User updated successfully!'
    else
      redirect_to edit_user_url(user), inertia: { errors: user.errors }
    end
  end

  private

  def user_params
    params.require(:user).permit(:name, :email, :password, :password_confirmation, :avatar)
  end
end

useForm Properties and Methods

Properties

| Property | Type | Description | |----------|------|-------------| | data | Object | Current form data | | errors | Object | Validation errors from server | | hasErrors | Boolean | Whether errors exist | | processing | Boolean | Whether form is submitting | | progress | Object | File upload progress | | wasSuccessful | Boolean | True after successful submission | | recentlySuccessful | Boolean | True for 2 seconds after success | | isDirty | Boolean | Whether form data has changed |

Methods

| Method | Description | |--------|-------------| | setData(key, value) | Set a single field value | | setData(values) | Set multiple field values | | reset() | Reset all fields to initial values | | reset(...fields) | Reset specific fields | | clearErrors() | Clear all validation errors | | clearErrors(...fields) | Clear specific field errors | | setError(field, message) | Set a custom error | | setError(errors) | Set multiple errors | | transform(callback) | Transform data before submission | | defaults() | Update default values for reset | | get(url, options) | Submit GET request | | post(url, options) | Submit POST request | | put(url, options) | Submit PUT request | | patch(url, options) | Submit PATCH request | | delete(url, options) | Submit DELETE request | | cancel() | Cancel an in-progress form submission |

Submission Options

form.post('/users', {
  // Preserve component state on validation errors
  preserveState: true,       // or 'errors' to preserve only on errors

  // Preserve scroll position
  preserveScroll: true,      // or 'errors' to preserve only on errors

  // Custom headers
  headers: { 'X-Custom': 'value' },

  // Force FormData even without files
  forceFormData: true,

  // Error bag for multiple forms on same page
  errorBag: 'createUser',

  // Event callbacks
  onBefore: (visit) => confirm('Submit form?'),
  onStart: (visit) => {},
  onProgress: (progress) => {},
  onSuccess: (page) => form.reset(),
  onError: (errors) => console.log(errors),
  onCancel: () => {},
  onFinish: () => {},
})

File Uploads

Inertia automatically converts forms with files to FormData:

const form = useForm({
  name: '',
  avatar: null,
  documents: [],  // Multiple files
})

// Single file
<input type="file" onChange={(e) => setData('avatar', e.target.files[0])} />

// Multiple files
<input
  type="file"
  multiple
  onChange={(e) => setData('documents', Array.from(e.target.files))}
/>

Upload Progress

<template>
  <div v-if="form.progress">
    <progress :value="form.progress.percentage" max="100" />
    <span>{{ form.progress.percentage }}%</span>
  </div>
</template>

File Uploads with PUT/PATCH

Some servers don't support multipart PUT/PATCH. Use method spoofing:

// Instead of form.put()
form.post(`/users/${user.id}`, {
  _method: 'put',  // Rails recognizes this
})

Nested Data

Use bracket notation for nested attributes:

const form = useForm({
  user: {
    name: '',
    profile: {
      bio: '',
    },
  },
})

// Access errors
form.errors['user.name']
form.errors['user.profile.bio']

Or with Rails-style params:

<input name="user[name]" v-model="form.user.name" />
<input name="user[profile][bio]" v-model="form.user.profile.bio" />

Multiple Forms on Same Page

Use error bags to isolate validation errors:

// Login form
const loginForm = useForm({ email: '', password: '' })
loginForm.post('/login', { errorBag: 'login' })

// Register form
const registerForm = useForm({ name: '', email: '', password: '' })
registerForm.post('/register', { errorBag: 'register' })

Server-side:

def create
  # ...
  redirect_to root_url, inertia: {
    errors: { login: { email: 'Invalid credentials' } }
  }
end

Access errors: page.props.errors.login.email

Form Transforms

Transform data before submission:

const form = useForm({
  first_name: 'John',
  last_name: 'Doe',
})

form
  .transform((data) => ({
    ...data,
    full_name: `${data.first_name} ${data.last_name}`,
  }))
  .post('/users')

The Form Component (Declarative)

For simpler forms, use the Form component:

Vue

<script setup>
import { Form } from '@inertiajs/vue3'
</script>

<template>
  <Form action="/users" method="post" v-slot="{ errors, processing }">
    <input type="text" name="name" />
    <span v-if="errors.name">{{ errors.name }}</span>

    <input type="email" name="email" />
    <span v-if="errors.email">{{ errors.email }}</span>

    <button type="submit" :disabled="processing">
      Submit
    </button>
  </Form>
</template>

React

import { Form } from '@inertiajs/react'

export default function CreateUser() {
  return (
    <Form action="/users" method="post">
      {({ errors, processing }) => (
        <>
          <input type="text" name="name" />
          {errors.name && <span>{errors.name}</span>}

          <input type="email" name="email" />
          {errors.email && <span>{errors.email}</span>}

          <button type="submit" disabled={processing}>
            Submit
          </button>
        </>
      )}
    </Form>
  )
}

Form Component Advanced Features (v3)

The Form component in v3 supports dotted notation for nested data and arrays:

import { Form } from '@inertiajs/react'

export default function CreateReport() {
  return (
    <Form action="/reports" method="post">
      {({ errors, processing, isDirty, wasSuccessful }) => (
        <>
          {/* Dotted notation for nested data */}
          <input type="text" name="report.title" />
          {errors['report.title'] && <span>{errors['report.title']}</span>}

          <input type="text" name="report.metadata.author" />

          {/* Array support */}
          <input type="text" name="tags[]" />
          <input type="text" name="tags[]" />

          {/* Disable inputs while processing */}
          <button type="submit" disabled={processing}>
            Submit
          </button>
        </>
      )}
    </Form>
  )
}

useFormContext Hook

Access form state from deeply nested components without prop drilling:

import { useFormContext } from '@inertiajs/react'

function SubmitButton() {
  const { processing, isDirty } = useFormContext()

  return (
    <button type="submit" disabled={processing || !isDirty}>
      {processing ? 'Saving...' : 'Save'}
    </button>
  )
}

Precognition (Real-Time Validation)

Validate forms server-side in real-time without duplicating validation rules on the client:

import { Form } from '@inertiajs/react'

export default function CreateUser() {
  return (
    <Form action="/users" method="post" precognition>
      {({ errors, valid, invalid, validate }) => (
        <>
          <input
            type="email"
            name="email"
            onBlur={() => validate('email')}
          />
          {valid('email') && <span className="text-green-500">✓</span>}
          {invalid('email') && <span className="text-red-500">{errors.email}</span>}

          <button type="submit">Create</button>
        </>
      )}
    </Form>
  )
}

Server-side:

# config/initializers/inertia_rails.rb
InertiaRails.configure do |config|
  config.precognition_prevent_writes = true  # Prevent DB writes during validation
end

Remembering Form State

Preserve form data across browser history navigation using useRemember.

The useRemember Hook

import { useRemember } from '@inertiajs/vue3'

// Form state persists across back/forward navigation
const form = useRemember({
  name: '',
  email: '',
  message: '',
})

Multiple Components on Same Page

Provide a unique key when multiple components use remember:

// Contact form
const contactForm = useRemember({
  email: '',
  message: '',
}, 'ContactForm')

// Newsletter form
const newsletterForm = useRemember({
  email: '',
}, 'NewsletterForm')

With useForm Helper

The form helper has built-in remember support:

// Pass a unique key as first argument
const form = useForm('CreateUser', {
  name: '',
  email: '',
  password: '',
})

// For edit forms, include the ID for uniqueness
const form = useForm(`EditUser:${props.user.id}`, {
  name: props.user.name,
  email: props.user.email,
})

Manual State Management

import { router } from '@inertiajs/vue3'

// Save state manually
router.remember({ step: 2, selections: ['a', 'b'] }, 'wizard-state')

// Restore state
const savedState = router.restore('wizard-state')
if (savedState) {
  // Restore component state from savedState
}

React Example

import { useRemember } from '@inertiajs/react'

export default function ContactForm() {
  const [form, setForm] = useRemember({
    name: '',
    email: '',
    message: '',
  }, 'ContactForm')

  return (
    <form>
      <input
        value={form.name}
        onChange={(e) => setForm({ ...form, name: e.target.value })}
      />
      {/* ... */}
    </form>
  )
}

The useHttp Hook (v3)

Make standalone HTTP requests without triggering Inertia page visits. Useful for API calls, background operations, and AJAX requests that don't need navigation.

React

import { useHttp } from '@inertiajs/react'

export default function SearchUsers() {
  const { data, post, processing, errors } = useHttp()
  const [query, setQuery] = useState('')
  const [results, setResults] = useState([])

  function search() {
    post('/api/search', {
      data: { query },
      onSuccess: (response) => setResults(response.data),
    })
  }

  return (
    <div>
      <input value={query} onChange={(e) => setQuery(e.target.value)} />
      <button onClick={search} disabled={processing}>
        {processing ? 'Searching...' : 'Search'}
      </button>
      {results.map(user => <div key={user.id}>{user.name}</div>)}
    </div>
  )
}

Key Differences from useForm

| Feature | useForm | useHttp | |---------|---------|---------| | Triggers navigation | Yes | No | | Returns promises | No | Yes | | Updates page props | Yes | No | | Reactive state | Yes | Yes | | File upload progress | Yes | Yes | | Precognition support | Yes | Yes |

Use useHttp when you need to make API requests that shouldn't cause a page transition.

Optimistic Updates (v3)

Update the UI immediately before the server responds, with automatic rollback on failure:

With router

import { router } from '@inertiajs/react'

function toggleLike(post) {
  router
    .optimistic((page) => {
      // Optimistically update the page props
      const postIndex = page.props.posts.findIndex(p => p.id === post.id)
      page.props.posts[postIndex].liked = !post.liked
      page.props.posts[postIndex].likes_count += post.liked ? -1 : 1
    })
    .post(`/posts/${post.id}/toggle-like`)
}

With Form component

<Form
  action={`/posts/${post.id}/toggle-like`}
  method="post"
  optimistic={(page) => {
    const p = page.props.posts.find(p => p.id === post.id)
    p.liked = !p.liked
  }}
>
  <button type="submit">
    {post.liked ? '❤️' : '🤍'} {post.likes_count}
  </button>
</Form>

With useForm

const form = useForm({})

form
  .optimistic((page) => {
    page.props.posts[0].title = 'Updated title'
  })
  .patch(`/posts/${post.id}`)

Optimistic updates automatically roll back if the server returns validation errors or a non-2xx response.

Best Practices

1. Always Use the PRG Pattern

# Incorrect - renders on POST
def create
  @user = User.create(user_params)
  render inertia: { user: @user }
end

# Correct - redirect after action
def create
  user = User.create(user_params)
  redirect_to user_url(user)
end

2. Return Minimal Error Data

# Only include field errors, not full model
redirect_to new_user_url, inertia: { errors: user.errors.to_hash }

3. Handle Validation on Client and Server

// Client-side for UX
const validateEmail = (email) => {
  if (!email.includes('@')) {
    form.setError('email', 'Invalid email format')
    return false
  }
  return true
}

function submit() {
  if (validateEmail(form.email)) {
    form.post('/users')  // Server validates too
  }
}

4. Preserve Scroll on Errors

form.post('/users', {
  preserveScroll: 'errors',  // Only preserve on validation errors
})

5. Reset Sensitive Fields on Success

form.post('/users', {
  onSuccess: () => form.reset('password', 'password_confirmation'),
})

6. Show Loading State

<button type="submit" :disabled="form.processing">
  <span v-if="form.processing">
    <Spinner /> Saving...
  </span>
  <span v-else>Save</span>
</button>

7. Confirm Destructive Actions

function deleteUser() {
  if (confirm('Are you sure?')) {
    router.delete(`/users/${user.id}`)
  }
}