Part 5 · 1 chapters · ~8 min

TypeORM, Sequelize, Kysely and MikroORM

TypeORM's mixed Data Mapper and Active Record, the EntityManager and metadata storage, the synchronize footgun, Sequelize's older model and hooks, Kysely as a type-safe query builder that is not an ORM, MikroORM's identity map and unit of work done properly in TypeScript, and choosing with evidence.

Four more, compared

	TypeORM	Sequelize	Kysely	MikroORM
kind	ORM (Data Mapper + Active Record)	ORM (Active Record)	query builder	ORM (Data Mapper)
schema	decorators on classes	model definitions	a TypeScript database interface (often generated)	decorators or defineEntity
identity map / unit of work	partial	no	no (by design)	yes, per request context
type safety of results	moderate	weak	strong	strong
watch out for	`synchronize: true` altering production schemas; lazy relations	hooks with side effects; ageing TypeScript support	you write every join yourself	flush semantics to learn

code

// the TypeORM footgun: never in production
new DataSource({ type: 'postgres', synchronize: true })   // diffs entities and ALTERs live tables on startup

// MikroORM: unit of work with a request-scoped EntityManager
const em = orm.em.fork();
const acct = await em.findOneOrFail(Account, id);
acct.balanceKobo -= amt;                                 // tracked
await em.flush();                                        // one UPDATE, in a transaction

Choosing with evidence: write the three hardest queries in your domain (a report, a locking transfer, a nested read) in each candidate and read the SQL each produces. That afternoon decides better than any feature table.