Context

We are migrating a backend from Laravel (PHP) to NestJS (Node.js) while continuing to use the same existing MySQL database.

The database is large and legacy, with:

• Hundreds of tables

• Some tables without primary keys

• Columns with complex or non-standard defaults (e.g., JSON stored in VARCHAR)

• A schema too large to comfortably manage in a single ORM schema file (≈19k+ lines)

Because of this size, Prisma was not suitable, so we decided to use TypeORM.

What We Tried

We attempted a DB-first approach using:

typeorm-model-generator@0.4.6
Node.js v24.x
MySQL 8.x
NestJS + TypeORM

Issues Encountered

1. Tables without primary keys

   • typeorm-model-generator fails or stops generation with:

     Table  has no PK.
     
     

   • These tables already exist and are used by the application.

2. Invalid generated TypeScript for certain defaults

   • Example:

     default: () => "'{"key":"value"}'"
     
     

   • This causes Prettier / TypeScript parse errors and breaks generation.

3. Manual entity creation is not viable

   • Recreating entities table-by-table introduces schema drift

   • Duplicate entities per module become hard to maintain

Why This Is a Problem

• The database schema cannot be immediately redesigned because we have around 300 tables

• Adding PKs or normalizing all tables is risky during migration

• We want a safe, incremental migration strategy

• We need to avoid runtime corruption or silent bugs

Question

1. What is the recommended approach for using TypeORM with a large legacy MySQL database that ?

Constraints

• DB schema changes must be minimal during migration

• Data integrity is critical

• Long-term maintainability is the goal