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name: fosmvvm-fluent-datamodel-generator description: Generate Fluent DataModels for FOSMVVM server-side persistence. Use when creating new database-backed entities, adding tables, or when the user mentions adding Models like Users, Ideas, Documents, etc. Uses fosmvvm-fields-generator for the Fields layer, then generates Fluent DataModel, migrations, and tests.

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?"

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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

Copy                    ┌─────────────────────────────────────┐
                    │         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

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File Structure

Each form-backed model requires files across multiple targets:

Copy── 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

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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

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File Templates

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

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Key Patterns

Fluent DataModel

Copyimport 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) are a code smell. Always ask "Is there any other way?" before using them.

For required relationships, use associated types in the protocol:

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

    var createdBy: User { get set }
}

In the Fluent model, @Parent directly satisfies the protocol:

Copyfinal 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:

Copyimport 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:

Copyprivate 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
}

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Naming Conventions

Common Field Types

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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

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Version History