Many-to-many

Students and courses

A student takes many courses; a course has many students. In SQL that needs a join table. In Prisma you model it explicitly — a model with two relations and a compound id — whenever the link carries data like a grade.

Explicit and implicit

model Student {
  id          Int          @id @default(autoincrement())
  name        String
  enrollments Enrollment[]
}

model Course {
  id          Int          @id @default(autoincrement())
  code        String       @unique
  enrollments Enrollment[]
}

model Enrollment {
  student   Student @relation(fields: [studentId], references: [id])
  studentId Int
  course    Course  @relation(fields: [courseId], references: [id])
  courseId  Int
  grade     Int?

  @@id([studentId, courseId])
}

// Implicit: no join model, Prisma manages a hidden _PostToTag table
model Post { id Int @id  tags Tag[] }
model Tag  { id Int @id  posts Post[] }

With an explicit model you query through it: include: { enrollments: { include: { course: true } } }.

Students and courses

Explicit and implicit

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