Prisma, prevent duplicated likes button?

Question

I don't want duplicate rows to be added to the database from users who have already clicked the like. What should I do?

I've seen it said to use upsert, but isn't upsert create if it doesn't exist and update if it exists?

If you update, there will be no duplicates, but doesn't it waste database resources anyway?

Answer 1

Here's the schema which you would need to define a constraint in which a user can like a post only one time.

generator client {
  provider = "prisma-client-js"
}

datasource db {
  provider = "postgresql"
  url      = env("DATABASE_URL")
}

model User {
  id    Int    @id @default(autoincrement())
  name  String
  email String @unique
  posts Post[]
  Like  Like[]
}

model Post {
  id        Int     @id @default(autoincrement())
  title     String
  published Boolean @default(true)
  author    User    @relation(fields: [authorId], references: [id])
  authorId  Int
  Like      Like[]
}

model Like {
  id     Int  @id @default(autoincrement())
  post   Post @relation(fields: [postId], references: [id])
  postId Int
  user   User @relation(fields: [userId], references: [id])
  userId Int

  @@unique([postId, userId])
}

Here a compound unique key is configured on the combination of postId and userId in Like Table.

If a user tries to like a post second time, the database would throw a unique constraint failed error.