generating-orm-code

ORM Code Generator

Overview

Generate type-safe ORM model classes, migration files, and repository patterns from existing database schemas or domain specifications. Supports Prisma, TypeORM, Sequelize, SQLAlchemy, Django ORM, and Drizzle ORM.

Prerequisites

• Database connection string or credentials for schema introspection
• psql or mysql CLI for querying information_schema
• Target ORM framework already installed in the project (prisma, typeorm, sqlalchemy, etc.)
• Node.js/Python/Go runtime matching the target ORM
• Existing project structure to place generated models in the correct directory

Instructions

1. Introspect the database schema by querying information_schema.COLUMNS, information_schema.TABLE_CONSTRAINTS, and information_schema.KEY_COLUMN_USAGE to extract all tables, columns, data types, nullable flags, defaults, primary keys, foreign keys, and unique constraints.

2. For PostgreSQL, additionally query pg_catalog.pg_type for custom enum types and pg_catalog.pg_index for index definitions. For MySQL, query information_schema.STATISTICS for index details.

3. Map database column types to ORM field types:

   • varchar/text -> String / @Column('text')
   • integer/bigint -> Int / @Column('int')
   • boolean -> Boolean / @Column('boolean')
   • timestamp/datetime -> DateTime / @Column('timestamp')
   • jsonb/json -> Json / @Column('jsonb')
   • uuid -> String with @default(uuid()) or uuid.uuid4
   • Custom enums -> Generate enum type definitions

4. Generate model classes with proper decorators/attributes:

   • For Prisma: Generate schema.prisma with model blocks, @id, @unique, @relation, and @default directives.
   • For TypeORM: Generate entity classes with @Entity(), @Column(), @PrimaryGeneratedColumn(), @ManyToOne(), @OneToMany() decorators.
   • For SQLAlchemy: Generate model classes extending Base with Column(), ForeignKey(), relationship(), and __tablename__.
   • For Drizzle: Generate table definitions with pgTable(), serial(), varchar(), timestamp(), and relations().

5. Generate relationship mappings from foreign key constraints. Detect one-to-one (unique FK), one-to-many, and many-to-many (junction table with two FKs) patterns automatically. Add both sides of each relationship with proper cascade options.

6. Create migration files that capture the current schema state. For Prisma: npx prisma migrate dev --name init. For TypeORM: generate migration with typeorm migration:generate. For Alembic: alembic revision --autogenerate.

7. Generate repository/service layer with common CRUD operations: findById, findAll with pagination, create, update, delete, and relationship-aware queries (findWithRelations).

8. Add validation decorators or constraints matching database CHECK constraints and NOT NULL columns. Use class-validator for TypeORM, Pydantic validators for SQLAlchemy, or Zod schemas for Prisma.

9. Generate TypeScript/Python type definitions or interfaces for API layer consumption, ensuring the ORM models and API types stay synchronized.

10. Validate generated models by running a test migration against a temporary database or by comparing the generated schema against the live database schema with a diff tool.

Output

• Model/entity files with full type annotations, decorators, and relationship mappings
• Migration files capturing the initial schema state
• Enum type definitions for database enum columns
• Repository/service classes with typed CRUD operations
• Validation schemas (Zod, class-validator, Pydantic) matching database constraints
• Type definition files for API layer consumption

Error Handling

Error	Cause	Solution
Circular relationship dependency	Two entities reference each other, causing import cycles	Use lazy loading (() => RelatedEntity) in TypeORM; use ForwardRef in SQLAlchemy; split into separate files with deferred imports
Unknown column type mapping	Database uses custom types, extensions, or domain types not in the standard mapping	Add custom type mapping in generator config; use @Column({ type: 'text' }) as fallback; register custom transformers
Migration conflicts with existing data	Generated migration adds NOT NULL columns without defaults	Add default values to new columns; create a two-phase migration (add nullable, backfill, set NOT NULL)
Junction table not detected as many-to-many	Junction table has extra columns beyond the two foreign keys	Model as an explicit entity with two ManyToOne relationships instead of an implicit ManyToMany
Schema drift between ORM models and database	Manual database changes not reflected in ORM code	Run introspection again; use prisma db pull or sqlacodegen to regenerate; diff against existing models

Examples

Prisma schema from PostgreSQL e-commerce database: Introspect 15 tables including users, orders, products, and categories. Generate schema.prisma with proper @relation directives, enum types for order status, and @default(autoincrement()) for serial columns. Output includes Zod validation schemas for each model.

TypeORM entities from MySQL SaaS application: Generate entity classes for a multi-tenant application with tenant isolation. Each entity includes a tenantId column with a custom @TenantAware decorator. Repository layer includes tenant-scoped query methods.

SQLAlchemy models from legacy database with naming conventions: Introspect a database with inconsistent naming (mix of camelCase and snake_case). Generate models with __tablename__ preserving original names while using Pythonic property names. Alembic migration captures the full schema.

Resources

• Prisma introspection: https://www.prisma.io/docs/orm/prisma-schema/introspection
• TypeORM entity documentation: https://typeorm.io/entities
• SQLAlchemy ORM tutorial: https://docs.sqlalchemy.org/en/20/orm/
• Drizzle ORM schema: https://orm.drizzle.team/docs/sql-schema-declaration
• Django inspectdb command: https://docs.djangoproject.com/en/5.0/howto/legacy-databases/