Relations & Migrations — Series 2

Preview — 3 of 10 questions

How do you define a one-to-one relation between User and Profile in Prisma?

javascript

model User {
  id      Int      @id @default(autoincrement())
  profile Profile?
}
model Profile {
  id     Int  @id @default(autoincrement())
  userId Int  @unique
  user   User @relation(fields: [userId], references: [id])
}

AThe foreign key side (Profile.userId) must be marked @unique — this is what distinguishes a one-to-one from a one-to-many relation in Prisma; without @unique on userId, this would instead be a one-to-many relation

BOne-to-one relations require both models to have @relation(fields:...) simultaneously

CPrisma has a dedicated @oneToOne decorator that must be added to both sides

DOne-to-one relations are not supported in Prisma; they must be modeled as one-to-many with an application-level uniqueness check

How do you model an Employee that optionally reports to another Employee (manager) in Prisma?

javascript

model Employee {
  id         Int        @id @default(autoincrement())
  name       String
  managerId  Int?
  manager    Employee?  @relation("EmployeeManager", fields: [managerId], references: [id])
  reports    Employee[] @relation("EmployeeManager")
}

ASelf-relations are not supported; Employee must reference a separate Manager model instead

BA named relation ("EmployeeManager" here) is required on a self-relation to distinguish the two different roles (manager side and reports side) the same model plays in the relationship — Prisma cannot infer which side is which without the name

CmanagerId must be a String type; self-relations don't support Int foreign keys

DThe relation name is purely cosmetic and can be omitted entirely for self-relations

What's the difference between onDelete: Cascade and onDelete: SetNull on a Prisma relation?

javascript

model Post {
  id       Int    @id @default(autoincrement())
  authorId Int?
  author   User?  @relation(fields: [authorId], references: [id], onDelete: SetNull)
}

ACascade and SetNull are interchangeable synonyms in Prisma

BSetNull deletes the parent record instead of the child when triggered

CCascade deletes the related child rows automatically when the parent is deleted; SetNull instead sets the foreign key column to NULL on the child rows, keeping them but detaching them from the deleted parent — SetNull requires the foreign key field to be optional (nullable)

DonDelete actions are enforced only by Prisma Client, never by the underlying database migration

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