FOSMVVM Fluent DataModel Generator

Generate Fluent DataModels for server-side persistence following FOSMVVM architecture.

Dependency: This skill uses fosmvvm-fields-generator for the Fields layer (protocol, messages, YAML). Run that skill first for form-backed models.

Scope Guard

This skill is specifically for Fluent persistence layer (typically in Vapor server apps).

STOP and ask the user if:

• The project doesn't use Fluent
• The target is iOS-only with CoreData, SwiftData, or Realm
• The user mentions a non-Fluent ORM or persistence layer
• You're unsure whether Fluent is the persistence layer

Check for Fluent indicators:

• Package.swift

  imports

  fluent

  ,

  fluent-postgres-driver

  ,

  fluent-sqlite-driver

  , etc.
• Existing models use

  @ID

  ,

  @Field

  ,

  @Parent

  ,

  @Children

  ,

  @Siblings

  property wrappers
• A

  Migrations/

  directory exists with Fluent migration patterns
• Imports include

  FluentKit

  or

  Fluent

If Fluent isn't present, inform the user: "This skill generates Fluent DataModels for server-side persistence. Your project doesn't appear to use Fluent. How would you like to proceed?"

When to Use This Skill

• User asks to create a new model/entity/table
• User wants to add a database-backed type (Users, Ideas, Documents, etc.)
• User mentions needing CRUD operations for a new concept
• Creating the persistence layer for a new entity

Architecture Context

In FOSMVVM, the Model is the center - the source of truth that reads and writes flow through.

See FOSMVVMArchitecture.md for full context.

DataModel in the Architecture

                    ┌─────────────────────────────────────┐
                    │         Fluent DataModel            │
                    │    (implements Model + Fields)      │
                    │                                     │
                    │  • All fields (system + user)       │
                    │  • Relationships (@Parent, etc.)    │
                    │  • Timestamps, audit fields         │
                    │  • Persistence logic                │
                    └──────────────┬──────────────────────┘
                                   │
              ┌────────────────────┼────────────────────────┐
              │                    │                        │
              ▼                    ▼                        ▼
    ┌─────────────────┐  ┌─────────────────┐    ┌─────────────────┐
    │ ViewModelFactory│  │  CreateRequest  │    │  UpdateRequest  │
    │   (projector)   │  │   RequestBody   │    │   RequestBody   │
    │                 │  │                 │    │                 │
    │ → ViewModel     │  │ → persists to   │    │ → updates       │
    │   (projection)  │  │   DataModel     │    │   DataModel     │
    └─────────────────┘  └─────────────────┘    └─────────────────┘

Fields vs DataModels

Fields protocol = Form input (user-editable subset)

• What users type into forms
• Validation, labels, placeholders
• NO relationships, NO system-assigned fields

DataModel = Complete entity (Fluent implementation)

• All fields including system-assigned (createdBy, timestamps)
• All relationships (@Parent, @Siblings, @Children)
• Fluent property wrappers, migrations, seeds

Not all entities need Fields:

• Session: system auth, no user form → DataModel-only
• Audit records: system-generated → DataModel-only
• Junction tables: pure storage → DataModel-only

File Structure

Each form-backed model requires files across multiple targets:

── fosmvvm-fields-generator ──────────────────────────────────
{ViewModelsTarget}/                  (shared protocol layer)
  FieldModels/
    {Model}Fields.swift              ← Protocol + Enum + Validation
    {Model}FieldsMessages.swift      ← Localization message struct

{ResourcesPath}/                     (localization resources)
  FieldModels/
    {Model}FieldsMessages.yml        ← YAML localization strings

── fosmvvm-fluent-datamodel-generator (this skill) ───────────
{WebServerTarget}/                   (server implementation)
  DataModels/
    {Model}.swift                    ← Fluent model (implements protocol)
  Migrations/
    {Model}+Schema.swift             ← Table creation migration
    {Model}+Seed.swift               ← Seed data migration

Tests/
  {ViewModelsTarget}Tests/
    FieldModels/
      {Model}FieldsTests.swift       ← Unit tests

database.swift                       ← Register migrations

How to Use This Skill

Invocation: /fosmvvm-fluent-datamodel-generator

Prerequisites:

• Model structure understood from conversation context
• Fields protocol exists (if form-backed model) via fosmvvm-fields-generator
• Relationships and system-assigned fields identified
• Fluent confirmed as the persistence layer

Workflow integration: This skill is used for server-side persistence with Fluent. For form-backed models, run fosmvvm-fields-generator first to create the Fields protocol. The skill references conversation context automatically—no file paths or Q&A needed.

Pattern Implementation

This skill references conversation context to determine DataModel structure:

Model Type Detection

From conversation context, the skill identifies:

• Entity purpose (user data, system records, audit logs, junction table)
• User input involvement (form-backed vs system-generated)
• Fields protocol requirement (if user edits this data)

Relationship Analysis

From requirements already in context:

• One-to-many relationships (@Parent in DataModel, not in Fields)
• Many-to-many relationships (Junction table + @Siblings, NOT UUID arrays)
• Relationship naming (self-documenting names, not vague references)

Field Classification

Based on data source:

• User-editable fields (from Fields protocol)
• System-assigned fields (createdBy, timestamps, status - DataModel only)
• Computed relationships (@Parent, @Children, @Siblings)

File Generation Order

If form-backed model (Fields protocol exists):

1. Fields layer already created via fosmvvm-fields-generator
2. DataModel implementation referencing Fields
3. Schema migration
4. Seed data migration
5. Tests
6. Migration registration

If system-only model (no Fields):

1. DataModel struct
2. Schema migration
3. Seed data migration (if needed)
4. Tests
5. Migration registration

Design Validation

Before generating, the skill validates:

1. Form requirement - System-generated entities skip Fields
2. Relationship patterns - Junction tables for many-to-many, @Parent for foreign keys
3. Naming clarity - Relationships have self-documenting names
4. Field separation - User fields in protocol, system fields in DataModel only

Context Sources

Skill references information from:

• Prior conversation: Model requirements, relationships discussed
• Fields protocol: If Claude has read Fields protocol into context or just created it
• Database schema: From codebase analysis of existing models
• Migration patterns: From existing migrations in project

File Templates

See reference.md for complete file templates with all patterns.

Key Patterns

Fluent DataModel

import FluentKit
import FOSFoundation
import FOSMVVM
import FOSMVVMVapor
import Foundation

final class {Model}: DataModel, {Model}Fields, Hashable, @unchecked Sendable {
    static let schema = "{models}"  // snake_case plural

    @ID(key: .id) var id: ModelIdType?

    // Fields from protocol
    @Field(key: "field_name") var fieldName: FieldType

    // Validation messages
    let {model}ValidationMessages: {Model}FieldsMessages

    // Timestamps
    @Timestamp(key: "created_at", on: .create) var createdAt: Date?
    @Timestamp(key: "updated_at", on: .update) var updatedAt: Date?

    // CRITICAL: Initialize validationMessages FIRST
    init() {
        self.{model}ValidationMessages = .init()
    }

    init(id: ModelIdType? = nil, fieldName: FieldType) {
        self.{model}ValidationMessages = .init()  // FIRST!
        self.id = id
        self.fieldName = fieldName
    }
}

Relationships (Associated Types Pattern)

PRINCIPLE: Existential types (

any Protocol

For required relationships, use associated types in the protocol:

public protocol IdeaFields: ValidatableModel, Codable, Sendable {
    associatedtype User: UserFields

    var createdBy: User { get set }
}

In the Fluent model,

@Parent

final class Idea: DataModel, IdeaFields, Hashable, @unchecked Sendable {
    @Parent(key: "created_by") var createdBy: User
    // No computed property needed - @Parent satisfies the associated type directly
}

In schema:

.field("created_by", .uuid, .required, .references(User.schema, "id", onDelete: .cascade))

When to use each pattern:

• Associated type (

  associatedtype User: UserFields

  ): Required relationships
• Optional associated type: Not supported - use

  ModelIdType?

  for optional FKs
• Plain

  ModelIdType

  : Optional FKs, external system references

Migrations

• Schema migration named:

  "{Model.schema}-initial"

• Seed migration named:

  "{Model.schema}-seed"

• Seed is environment-aware (debug, test, release)
• Seed is idempotent:

  guard count() == 0

Raw SQL in Migrations (PostgreSQL Features)

For PostgreSQL-specific features (tsvector, LTREE, etc.), use SQLKit:

import Fluent
import SQLKit  // Required for raw SQL

// In prepare():
guard let sql = database as? any SQLDatabase else { return }

let schema = Model.schema
try await sql.raw(SQLQueryString("ALTER TABLE \(unsafeRaw: schema) ADD COLUMN search_vector tsvector")).run()

Key points:

• Import

  SQLKit

  (not just

  Fluent

  )
• Cast database:

  database as? any SQLDatabase

• Use

  SQLQueryString

  with

  \(unsafeRaw:)

  for identifiers
• These columns are database-only (not in protocol or Fluent model)

Tests

• Use

  @Suite

  annotation with descriptive name
• Conform to

  LocalizableTestCase

• Test all form fields
• Test validation with

  @Test(arguments:)

• Create private test struct implementing the Fields protocol

Test structs with associated types:

private struct TestIdea: IdeaFields {
    typealias User = TestUser  // Satisfy the associated type

    var id: ModelIdType?
    var createdBy: TestUser    // Concrete type, not existential
}

private struct TestUser: UserFields {
    var id: ModelIdType? = .init()
    var firstName: String = "Test"
    // ... other required fields with defaults
}

Naming Conventions

User

Idea

users

ideas

created_at

user_id

searchLanguage

inProgress

"search_language"

"in_progress"

{Model}Fields

UserFields

IdeaFields

{Model}FieldsMessages

UserFieldsMessages

Common Field Types

String

.string

VARCHAR/TEXT

Int

.int

INTEGER

Bool

.bool

BOOLEAN

Date

.datetime

TIMESTAMPTZ

UUID

.uuid

UUID

[UUID]

.array(of: .uuid)

UUID[]

.string

VARCHAR

JSONB

.json

JSONB

See Also

• FOSMVVMArchitecture.md - Full FOSMVVM architecture
• fosmvvm-fields-generator - For form validation (Fields protocols)
• fosmvvm-viewmodel-generator - For ViewModels that project from DataModels
• reference.md - Complete file templates

Version History