How to define and work with self-relations in Prisma.

A relation field can reference its own model, called a self-relation. Self-relations can be 1-1, 1-n, or m-n.

model User {
  id          Int     @id @default(autoincrement())
  name        String?
  successorId Int?    @unique
  successor   User?   @relation("BlogOwnerHistory", fields: [successorId], references: [id])
  predecessor User?   @relation("BlogOwnerHistory")
}

This expresses:

• A user can have zero or one predecessor
• A user can have zero or one successor

Key rules:

• Both sides must use the same @relation name
• One side must be fully annotated with fields and references
• The foreign key needs @unique for 1-1
• Cannot be required on both sides (impossible to create first record)

model User {
  id        Int     @id @default(autoincrement())
  name      String?
  teacherId Int?
  teacher   User?   @relation("TeacherStudents", fields: [teacherId], references: [id])
  students  User[]  @relation("TeacherStudents")
}

This expresses:

• A user has zero or one teacher
• A user can have zero or more students

No @unique constraint on teacherId - multiple students can share the same teacher.

model User {
  id         Int     @id @default(autoincrement())
  name       String?
  followedBy User[]  @relation("UserFollows")
  following  User[]  @relation("UserFollows")
}

This expresses:

• A user can be followed by zero or more users
• A user can follow zero or more users

For relational databases, this is an implicit m-n (Prisma manages the relation table).

Explicit version (for storing additional fields):

model User {
  id         Int       @id @default(autoincrement())
  name       String?
  followedBy Follows[] @relation("followedBy")
  following  Follows[] @relation("following")
}

model Follows {
  followedBy   User @relation("followedBy", fields: [followedById], references: [id])
  followedById Int
  following    User @relation("following", fields: [followingId], references: [id])
  followingId  Int
  @@id([followingId, followedById])
}

You can combine multiple self-relations:

model User {
  id         Int     @id @default(autoincrement())
  name       String?
  teacherId  Int?
  teacher    User?   @relation("TeacherStudents", fields: [teacherId], references: [id])
  students   User[]  @relation("TeacherStudents")
  followedBy User[]  @relation("UserFollows")
  following  User[]  @relation("UserFollows")
}