prisma 中隐式或显式的多对多关系

## 使用Prisma进行多对多关系的隐式和显式操作

typescript
// Prisma模型定义
model User {
  id    Int    @id @default(autoincrement())
  name  String
  posts Post[]
}
model Post {
  id     Int      @id @default(autoincrement())
  title  String
  body   String
  author User     @relation(fields: [authorId], references: [id])
  authorId Int
}
// 隐式多对多关系
model Category {
  id    Int    @id @default(autoincrement())
  name  String
  posts Post[]
}

typescript
// Prisma模型定义
model Student {
  id    Int    @id @default(autoincrement())
  name  String
  coursesEnrolled CourseEnrollment[]
}
model Course {
  id     Int    @id @default(autoincrement())
  title  String
  studentsEnrolled CourseEnrollment[]
}
// 显式多对多关系
model CourseEnrollment {
  student   Student @relation(fields: [studentId], references: [id])
  studentId Int
  course    Course  @relation(fields: [courseId], references: [id])
  courseId  Int
  createdAt DateTime @default(now())
  updatedAt DateTime @updatedAt
}