How it works

The seeder library fills entity properties with generated data. You describe what data each property should hold (using @Seed() decorators on your entities), then call a seeding method. The library builds fully populated instances — including all related entities — in one call.

The four seeding methods

All seeding flows through four methods on the seed() builder:

Method	Quantity	What you get
create()	One	Built and returned directly — no database
createMany(n)	Many	Array built and returned directly — no database
save()	One	Written to the database, then returned
saveMany(n)	Many	Array written to the database, then returned

All four methods read your @Seed() decorators and auto-seed relations. The difference is whether the result is persisted: create and createMany build and return entities directly; save and saveMany write to the database first, then return the persisted result.

Mental model

Think of seeding in three steps:

1. Describe — annotate entity properties with @Seed():

@Entity()
class Author {
  @Seed(() => faker.person.fullName())  // ← describe
  @Column()
  name!: string

  @Seed({ count: 3 })  // ← describe
  @OneToMany(() => Book, (b) => b.author)
  books!: Book[]
}

2. Call — pick a method and supply options:

const author = await seed(Author).create()                     // returned directly
const authors = await seed(Author).createMany(5)               // array returned directly
const author = await seed(Author).save({ dataSource })         // persisted, then returned
const authors = await seed(Author).saveMany(5, { dataSource }) // array persisted, then returned

3. Use — the returned instance(s) have all properties populated:

author.name      // "John Smith" (from @Seed factory)
author.books     // [Book, Book, Book] (seeded automatically)
author.id        // assigned by the database (only set after save)

Relations are seeded automatically — the library detects cycles and stops before infinite loops.

Next steps

• Decorating entities to learn @Seed() syntax in detail
• Seeding entities for detailed options on each method (relations, values, etc.)
• Seeder suites to organize multiple seeders with dependencies