Self-relations

Source URL: https://docs.prisma.io/docs/orm/prisma-schema/data-model/relations/self-relations

Self-relations

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.

Self-relations always require the @relation attribute.

One-to-one self-relations

    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)

One-to-many 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")
    }

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.

Many-to-many self relations

    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])
    }

Multiple self-relations on same model

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")
    }