Backend Model Creation

This skill creates Mongoose models following established patterns with proper typing from @{project}/types.

Overview

Models follow a types-first approach:

1. Define TypeScript types in @{project}/types
2. Create Mongoose model in backend importing those types
3. Use shared enum options for validation

File Structure

libs/types/src/
├── lib/
│   ├── Workflow.ts         # Type definitions
│   └── {Resource}.ts       # New resource types
└── index.ts                # Re-exports

apps/backend/src/models/
├── _utils.ts               # generateId, stripId helpers
├── Workflow.ts             # Mongoose model
└── {Resource}.ts           # New resource model

Step 1: Create Types in @{project}/types

Create libs/types/src/lib/{Resource}.ts:

// Define enum options as const arrays (used for both TS types and Mongoose validation)
export const ResourceStatusOptions = ['active', 'inactive', 'archived'] as const;
export type ResourceStatus = typeof ResourceStatusOptions[number];

// Optional: Additional enum options
export const ResourcePriorityOptions = ['low', 'medium', 'high'] as const;
export type ResourcePriority = typeof ResourcePriorityOptions[number];

// Subdocument types (if needed)
export type ResourceMetadata = {
  source?: string;
  tags?: string[];
  priority?: ResourcePriority;
};

// Main entity type
export type Resource = {
  id: string;
  name: string;
  description?: string;
  status: ResourceStatus;
  metadata?: ResourceMetadata;
  createdAt: Date;
  updatedAt: Date;
};

Export from libs/types/src/index.ts:

export * from './lib/Resource';

Step 2: Create the Mongoose Model

Create apps/backend/src/models/{Resource}.ts:

import { Schema, model, Document, Types } from 'mongoose';
import {
  Resource as IResource,
  ResourceStatusOptions,
  ResourcePriorityOptions,
} from '@{project}/types';
import { generateId, stripId } from './_utils';

// Subdocument schema (if needed)
const MetadataSchema = new Schema(
  {
    source: { type: String },
    tags: { type: [String], default: undefined },
    priority: { type: String, enum: ResourcePriorityOptions },
  },
  { _id: false }
);

// Main schema
const resourceSchema = new Schema<IResource>(
  {
    id: { type: String, required: true, unique: true, index: true, default: generateId },
    name: { type: String, required: true },
    description: { type: String },
    status: { type: String, enum: ResourceStatusOptions, required: true, default: 'active' },
    metadata: { type: MetadataSchema },
    createdAt: { type: Date, default: Date.now },
    updatedAt: { type: Date, default: Date.now },
  },
  {
    id: false,           // Disable Mongoose's virtual id (we use our own)
    versionKey: false,   // Disable __v field
    toJSON: { transform: stripId },
    toObject: { transform: stripId },
  }
);

// Compound indexes for common queries
resourceSchema.index({ status: 1, createdAt: -1 });

// Pre-save hook to update timestamp (Mongoose 8+ - no next() callback)
resourceSchema.pre('save', function () {
  this.updatedAt = new Date();
});

// Export document type for services
export type ResourceDocument = Document<unknown, object, IResource> &
  IResource & { _id: Types.ObjectId };

const Resource = model<IResource>('Resource', resourceSchema);
export default Resource;

Key Patterns

Utilities from _utils.ts

Always import from _utils:

import { generateId, stripId } from './_utils';

• generateId: UUID v4 wrapper for generating unique IDs
• stripId: Transform helper to remove _id from JSON/object output

ID Field Pattern

Always use this pattern for the id field:

id: { type: String, required: true, unique: true, index: true, default: generateId },

Enum Options Pattern

Define options as const arrays in types:

// In @{project}/types
export const StatusOptions = ['active', 'inactive'] as const;
export type Status = typeof StatusOptions[number];

// In Mongoose model
import { StatusOptions } from '@{project}/types';
status: { type: String, enum: StatusOptions, required: true, default: 'active' },

Schema Options

Always include these options to ensure clean API responses:

{
  id: false,           // Disable Mongoose's virtual id
  versionKey: false,   // Disable __v field
  toJSON: { transform: stripId },
  toObject: { transform: stripId },
}

Subdocument Schemas

For embedded documents, always disable _id:

const AddressSchema = new Schema(
  {
    street: { type: String, required: true },
    city: { type: String, required: true },
    zipCode: { type: String },
  },
  { _id: false }
);

// Use in main schema
address: { type: AddressSchema }

Array Fields

For optional arrays, use default: undefined to avoid empty arrays:

tags: { type: [String], default: undefined },

For required arrays with default empty:

items: { type: [ItemSchema], required: true, default: [] },

Indexes

Single field indexes:

id: { type: String, index: true },

Compound indexes (add after schema definition):

// Put equality filters first, then sort fields
resourceSchema.index({ status: 1, createdAt: -1 });
resourceSchema.index({ userId: 1, status: 1 });

Pre-save Hook

Mongoose 8+ uses synchronous hooks (no next() callback):

resourceSchema.pre('save', function () {
  this.updatedAt = new Date();
});

Document Type Export

Export the document type for use in services:

export type ResourceDocument = Document<unknown, object, IResource> &
  IResource & { _id: Types.ObjectId };

Complete Example

Types (libs/types/src/lib/Project.ts)

export const ProjectStatusOptions = ['planning', 'active', 'completed', 'archived'] as const;
export type ProjectStatus = typeof ProjectStatusOptions[number];

export const ProjectPriorityOptions = ['low', 'medium', 'high', 'critical'] as const;
export type ProjectPriority = typeof ProjectPriorityOptions[number];

export type ProjectMember = {
  userId: string;
  role: 'owner' | 'editor' | 'viewer';
  joinedAt: Date;
};

export type Project = {
  id: string;
  name: string;
  description?: string;
  status: ProjectStatus;
  priority: ProjectPriority;
  members: ProjectMember[];
  ownerId: string;
  startDate?: Date;
  dueDate?: Date;
  completedAt?: Date;
  createdAt: Date;
  updatedAt: Date;
};

Model (apps/backend/src/models/Project.ts)

import { Schema, model, Document, Types } from 'mongoose';
import {
  Project as IProject,
  ProjectStatusOptions,
  ProjectPriorityOptions,
} from '@{project}/types';
import { generateId, stripId } from './_utils';

// Member subdocument schema
const MemberSchema = new Schema(
  {
    userId: { type: String, required: true },
    role: { type: String, enum: ['owner', 'editor', 'viewer'], required: true },
    joinedAt: { type: Date, default: Date.now },
  },
  { _id: false }
);

// Main Project schema
const projectSchema = new Schema<IProject>(
  {
    id: { type: String, required: true, unique: true, index: true, default: generateId },
    name: { type: String, required: true },
    description: { type: String },
    status: { type: String, enum: ProjectStatusOptions, required: true, default: 'planning' },
    priority: { type: String, enum: ProjectPriorityOptions, required: true, default: 'medium' },
    members: { type: [MemberSchema], required: true, default: [] },
    ownerId: { type: String, required: true, index: true },
    startDate: { type: Date },
    dueDate: { type: Date },
    completedAt: { type: Date },
    createdAt: { type: Date, default: Date.now },
    updatedAt: { type: Date, default: Date.now },
  },
  {
    id: false,
    versionKey: false,
    toJSON: { transform: stripId },
    toObject: { transform: stripId },
  }
);

// Indexes
projectSchema.index({ ownerId: 1, status: 1 });
projectSchema.index({ status: 1, dueDate: 1 });

// Pre-save hook
projectSchema.pre('save', function () {
  this.updatedAt = new Date();
});

// Document type
export type ProjectDocument = Document<unknown, object, IProject> &
  IProject & { _id: Types.ObjectId };

const Project = model<IProject>('Project', projectSchema);
export default Project;

Checklist

After creating a new model:

1. Create types in libs/types/src/lib/{Resource}.ts
   • Define enum options as const arrays
   • Define subdocument types if needed
   • Define main entity type
2. Export types from libs/types/src/index.ts
3. Build types library: npx tsc -b libs/types/tsconfig.lib.json
4. Create model in apps/backend/src/models/{Resource}.ts
   • Import types and enum options from @{project}/types
   • Import generateId and stripId from ./_utils
   • Create subdocument schemas with { _id: false }
   • Add schema options: id: false, versionKey: false, transforms
   • Add indexes for common queries
   • Add pre-save hook for updatedAt
   • Export document type
5. Create API schemas (if needed) in libs/types/src/api/{resource}.ts (see backend-route-creation skill)
6. Create routes (if needed) in apps/backend/src/routes/{resource}.ts (see backend-route-creation skill)