FOSMVVM Fields Generator

Generate Form Specifications following FOSMVVM patterns.

Conceptual Foundation

For full architecture context, see FOSMVVMArchitecture.md

A Form Specification (implemented as a {Name}Fields protocol) is the single source of truth for user input. It answers:

1. What data can the user provide? (properties)
2. How should it be presented? (FormField with type, keyboard, autofill semantics)
3. What constraints apply? (validation rules)
4. What messages should be shown? (localized titles, placeholders, errors)

Why This Matters

The Form Specification is defined once, used everywhere:

// Same protocol adopted by different consumers:
struct CreateIdeaRequestBody: ServerRequestBody, IdeaFields { ... }  // HTTP transmission
@ViewModel struct IdeaFormViewModel: IdeaFields { ... }              // Form rendering
final class Idea: Model, IdeaFields { ... }                          // Persistence validation

This ensures:

• Consistent validation - Same rules on client and server
• Shared localization - One YAML file, used everywhere
• Single source of truth - Change once, applies everywhere

Connection to FOSMVVM

Form Specifications integrate with:

• Localization System - FormField titles/placeholders and validation messages use LocalizableString
• Validation System - Implements ValidatableModel protocol
• Request System - RequestBody types adopt Fields for validated transmission
• ViewModel System - ViewModels adopt Fields for form rendering

When to Use This Skill

• Defining a new form (create, edit, filter, search)
• Adding validation to a request body
• Any type that needs to conform to ValidatableModel
• When fosmvvm-fluent-datamodel-generator needs form fields for a DataModel

What This Skill Generates

A complete Form Specification consists of 3 files:

Project Structure Configuration

Replace placeholders with your project's actual paths:

Expected Structure:

Sources/
  {ViewModelsTarget}/
    FieldModels/
      {Name}Fields.swift
      {Name}FieldsMessages.swift
  {ResourcesPath}/
    FieldModels/
      {Name}FieldsMessages.yml

Generation Process

Step 1: Understand the Form Purpose

Before generating, clarify:

• What is this form for? (create, edit, filter, login, etc.)
• What entity does it relate to? (User, Idea, Document, etc.)
• Name should reflect purpose: CreateIdea, UpdateProfile, LoginCredentials

Step 2: Gather Field Requirements

For each field, determine:

• Property name and type (String, Int, Date, enum, optional?)
• Presentation - What FormFieldType? What FormInputType?
• Constraints - Required? Length range? Value range? Date range?
• Localization - Title, placeholder, error messages

Step 3: Generate Files in Order

1. {Name}Fields.swift - The protocol and validation logic
2. {Name}FieldsMessages.swift - The localized message struct
3. {Name}FieldsMessages.yml - The actual localized strings

Step 4: Verify

After generation:

1. Run swift build to verify compilation
2. Check YAML keys match Swift property paths

Key Patterns

Protocol Structure

public protocol {Name}Fields: ValidatableModel, Codable, Sendable {
    var fieldName: FieldType { get set }
    var {name}ValidationMessages: {Name}FieldsMessages { get }
}

FormField Definition

static var contentField: FormField<String?> { .init(
    fieldId: .init(id: "content"),
    title: .localized(for: {Name}FieldsMessages.self, propertyName: "content", messageKey: "title"),
    placeholder: .localized(for: {Name}FieldsMessages.self, propertyName: "content", messageKey: "placeholder"),
    type: .textArea(inputType: .text),
    options: [
        .required(value: true)
    ] + FormInputOption.rangeLength(contentRange)
) }

FormField Types Reference

FormInputType Reference (common ones)

Validation Method Pattern

internal func validateContent(_ fields: [FormFieldBase]?) -> [ValidationResult]? {
    guard fields == nil || (fields?.contains(Self.contentField) == true) else {
        return nil
    }

    var result = [ValidationResult]()

    if content.isEmpty {
        result.append(.init(
            status: .error,
            field: Self.contentField,
            message: {name}ValidationMessages.contentRequiredMessage
        ))
    } else if !Self.contentRange.contains(NSString(string: content).length) {
        result.append(.init(
            status: .error,
            field: Self.contentField,
            message: {name}ValidationMessages.contentOutOfRangeMessage
        ))
    }

    return result.isEmpty ? nil : result
}

Messages Struct Pattern

@FieldValidationModel public struct {Name}FieldsMessages {
    @LocalizedString("content", messageGroup: "validationMessages", messageKey: "required")
    public var contentRequiredMessage

    @LocalizedString("content", messageGroup: "validationMessages", messageKey: "outOfRange")
    public var contentOutOfRangeMessage
}

YAML Structure

en:
  {Name}FieldsMessages:
    content:
      title: "Content"
      placeholder: "Enter your content..."
      validationMessages:
        required: "Content is required"
        outOfRange: "Content must be between 1 and 10,000 characters"

Naming Conventions

Collaboration Protocol

1. Clarify the form purpose first (what is this form for?)
2. Confirm field list with types and constraints
3. Generate one file at a time with feedback
4. The implementer will wire the protocol to their consumer types

See Also

• FOSMVVMArchitecture.md - Full FOSMVVM architecture reference
• fosmvvm-viewmodel-generator - For ViewModels that adopt Fields
• fosmvvm-fluent-datamodel-generator - For Fluent DataModels that implement Fields
• reference.md - Complete file templates

Version History