Scaffolding Data Layer

Scaffolding the Modern Data Layer

Translate legacy data models (Mongoose, Sequelize, etc.) into a modern, type-safe data access layer using TypeScript and Zod.

Objective

Recreate the legacy data structures in a way that provides runtime validation and full TypeScript support, while accounting for Schema Evolution and potential "Dirty Data" in the legacy system.

Instructions for the Scaffold Subagent

Copy this checklist and track your progress:

Task Progress:
- [ ] Step 1: Analyze Audit Specs
- [ ] Step 2: Perform Data Integrity Audit (Draft)
- [ ] Step 3: Initialize Database Connection
- [ ] Step 4: Define Zod Schemas & TypeScript Types
- [ ] Step 5: Implement Data Access Utilities

Step 1. Analyze Audit Specs

Locate and read docs/legacy-audit/Data_Models.md. Identify:

• Primary Entities and their relationships (One-to-Many, Many-to-Many).
• Validation Rules: Required fields, regex patterns, min/max values.
• Middleware Hooks: Legacy pre-save or post-remove logic that needs to be manually ported to the service layer.

Step 2. Perform Data Integrity Audit

Before writing code, you MUST ensure the modern schemas are compatible with the existing legacy data.

• Strategy: Run the new Zod validation schemas against actual records in the legacy database.
• Outcome: Identify "Dirty Data" gaps (e.g., missing required fields in old records, inconsistent types) and use z.optional() or .nullable() to maintain compatibility with legacy data patterns.

Step 3. Connect to Legacy Database

Create src/lib/db/mongodb.ts (or the appropriate client).

• Configuration: Ensure the connection string (usually via MONGODB_URI in .env.local) points to the legacy-app's database.
• Pattern: Export a cached client promise (Singleton pattern) to avoid opening too many connections during HMR (Hot Module Replacement) in Next.js development.

// Example: src/lib/db/mongodb.ts
import { MongoClient } from "mongodb";

if (!process.env.MONGODB_URI) {
  throw new Error('Invalid/Missing environment variable: "MONGODB_URI"');
}

const uri = process.env.MONGODB_URI;
// ... (Rest of singleton implementation)

Step 4. Define Zod Schemas & TypeScript Types

Create src/lib/models/schema.ts (Zod) and src/lib/models/types.ts (TypeScript).

• Zod First: Define the schema using Zod for runtime validation.
• Type Inference: Use z.infer<typeof Schema> to generate your TypeScript types automatically.
• Relationship Mapping: Convert legacy ORM relationships (e.g., Mongoose Refs) into manual link logic using ObjectId from the native driver.

Step 5. Implement Data Access Utilities

Create src/lib/models/utils.ts for logic that was previously buried in the ORM (e.g., password hashing, complex queries, virtual field calculation).

• Static Utilities: Native drivers lack "Model Methods." All logic must be extracted into pure functions that take the data object as an argument.