3.4 KiB
3.4 KiB
Form Fragments & Composition
Reusable form components, modular form building, and constraint management.
Files
Fragments (Reusable Components)
- header.toml - Header/intro section
- custom_border_section.toml - Styled section template
- fancy_border_section.toml - Advanced border styling
- employee_info_section.toml - Employee data fields
- agreement_section.toml - Legal/policy acceptance
- support_section.toml - Support tier selection
- premium_section.toml - Premium features section
- enterprise_section.toml - Enterprise tier section
Examples Using Fragments
- form_with_groups_includes.toml - Demonstrates fragment inclusion
- array-trackers.toml - RepeatingGroup arrays with constraint interpolation
Constraint Configuration
- constraints.toml - Single source of truth for array validation limits
Usage Pattern
Include Fragments in Your Forms
# main_form.toml
[includes]
header = "fragments/header.toml"
employee = "fragments/employee_info_section.toml"
agreement = "fragments/agreement_section.toml"
[sections.main]
title = "Employee Onboarding"
```text
### Build Complex Forms from Reusable Parts
```bash
# Each fragment can be tested independently
cargo run --example form_with_groups_includes
```text
## Constraint Interpolation Example
### What is Constraint Interpolation
Instead of hardcoding validation limits in forms, you can use constraint variables:
```toml
# array-trackers.toml
[[elements]]
name = "udp_trackers"
type = "repeatinggroup"
max_items = "${constraint.tracker.udp.max_items}" # ← Dynamic constraint reference
```text
### Single Source of Truth
All validation limits are defined in **one file**:
```toml
# constraints.toml
[tracker.udp]
max_items = 4 # Change this value, form auto-updates!
```text
### How It Works
1. **Form loads** - `array-trackers.toml` contains `"${constraint.tracker.udp.max_items}"`
2. **Parser resolves** - Form parser finds `constraints.toml` in same directory
3. **Value injected** - The constraint value (4) replaces the placeholder
4. **Form validates** - User can add up to 4 UDP trackers
### Try It
```bash
# Run the example
cargo run --example array-trackers
# The form will allow
# - 0-4 UDP trackers (from constraints.tracker.udp.max_items)
# - 0-4 HTTP trackers (from constraints.tracker.http.max_items)
# Change constraints.toml
# [tracker.udp]
# max_items = 6 # ← Change from 4 to 6
#
# Re-run the example - form now allows 0-6 UDP trackers!
```text
### Key Files
- **constraints.toml** - Defines validation limits
- **array-trackers.toml** - References constraints via `${constraint.path}`
- Form parser automatically resolves interpolations at load time
## Benefits of Constraints
- **DRY** - Write common sections once
- **Maintainability** - Update fragments in one place
- **Reusability** - Share across multiple forms
- **Modularity** - Compose complex forms from simple parts
- **Consistency** - Unified styling and structure
- **Constraint Sync** - Single place to change validation limits (all layers auto-sync)
## Fragment Library
Use these as templates for your own fragments:
| Fragment | Purpose | Fields |
|----------|---------|--------|
| header | Form introduction | Title, description |
| employee_info | Standard employee data | Name, email, phone |
| agreement | Policy acceptance | Checkbox, text |
| support | Tier selection | Radio buttons |
| border_section | Custom styled container | Any fields |