Seeding entities

The seed(EntityClass) function returns a builder with four methods: create, createMany, save, and saveMany. Entities are populated according to their @Seed() decorators — see Decorating entities to learn how to write those.

import { seed } from '@joakimbugge/mikroorm-seeder'

Creating without saving

create() and createMany() build entity instances without touching the database. Useful for unit tests or for preparing entities before passing them to your own persistence logic.

const author = await seed(Author).create()
// Plain Author instance — no id, fully populated relations

const books = await seed(Book).createMany(10)
// [Book, Book, …] — each with its own seeded Author

Saving to the database

save() and saveMany() create instances and write them to the database in one step. Pass an EntityManager in the options.

const author = await seed(Author).save({ em })
// author.id  → assigned by the database
// author.books → 3 persisted Book instances

const authors = await seed(Author).saveMany(5, { em })
// [Author, Author, Author, Author, Author] — each with their own books

Seeding multiple entity types at once

Pass an array of entity classes to seed one of each:

const [author, book] = await seed([Author, Book]).create()
const [author, book] = await seed([Author, Book]).save({ em })

Relation seeding is disabled by default in this form — each entity is created independently, so there is no overlap between the Author you asked for and the Author that would have been auto-created inside Book. Pass relations: true to override:

const [author, book] = await seed([Author, Book]).save({ em, relations: true })
// author.books → seeded  |  book.author → seeded (independently)

createMany and saveMany return an array per class:

const [authors, books] = await seed([Author, Book]).createMany(3)
// authors → [Author, Author, Author]
// books   → [Book, Book, Book]

Disabling relation seeding

Pass relations: false to create a flat entity with no relation properties set — useful when you want to wire relations yourself or need to seed only the primary entity:

const author = await seed(Author).create({ relations: false })
// author.books → undefined

const book = await seed(Book).save({ em, relations: false })
// book.author → null in the database

Overriding seeded values

Pass a values map to inject specific values after all @Seed factories have run. This works for properties with @Seed() decorators and for properties with no decorator at all:

// Status is set even if Booking has no @Seed on it
const booking = await seed(Booking).create({ values: { status: 'confirmed' } })
const booking = await seed(Booking).save({ em, values: { user, status: 'confirmed' } })

// All 5 get the same user
const bookings = await seed(Booking).createMany(5, { values: { user } })
const bookings = await seed(Booking).saveMany(5, { em, values: { user } })

Each property in values can also be a factory function — it is called once per entity, so every instance can receive a unique generated value:

const bookings = await seed(Booking).saveMany(10, {
  em,
  values: {
    price: () => faker.number.float({ min: 10, max: 500 }), // unique per booking
    status: 'confirmed',                                     // same for all
  },
})

Factory entries in values receive the same (context, self, index) arguments as @Seed factories, so you can read already-applied properties from self, query the database via context.em, or use the sequence index to generate unique values per entity.

When a property has both a @Seed factory and a values entry, the @Seed factory still runs but its result is overwritten by values.

INFO

values are applied after all @Seed factories have finished, so they are never visible on self inside a @Seed factory callback.

Running a seed script?

See Running scripts for how to execute seed code directly with Node.js or ts-node, including the reflect-metadata import requirement and TypeScript execution options.