docs: add auto-generated primary key sample for Prisma (GoogleCloudPlatform#3085)

Add a model that uses an auto-generated primary key to the Prisma sample
application.

Author: olavloite

samples/nodejs/prisma-sample-app/README.md

@@ -121,7 +121,7 @@ The following limitations are currently known:
 | Migrations             | Cloud Spanner does not support the full PostgreSQL DDL dialect, and also not all `pg_catalog` tables and functions. PGAdapter contains translations for the most commonly used features that are not supported. It is possible to use Prisma Migrations with PGAdapter, but some migrations are likely to require manual modifications. |
 | Shadow Database        | Cloud Spanner cannot be used as a shadow database. Instead, you need to set up a real PostgreSQL database and use that as the shadow database. See https://www.prisma.io/docs/concepts/components/prisma-migrate/shadow-database#cloud-hosted-shadow-databases-must-be-created-manually                                                 |
 | Advisory locks         | Advisory locks are not supported. Prisma will try to use this during migrations. These commands will be ignored by PGAdapter.                                                                                                                                                                                                           |
-| Generated primary keys | Auto-generated primary keys are not supported. Do not add the `@default(autoincrement())` annotation to your model definitions.                                                                                                                                                                                                         |
+| Generated primary keys | Auto-generated primary keys are supported, but do not generate a monotonically increasing value. The `@default(autoincrement())` annotation in combination with the `serial` data type will generate bit-reversed sequential values that are safe from causing hotspots in your database.                                               |
 | Upsert                 | Upsert is not supported.                                                                                                                                                                                                                                                                                                                |
 
 ### Migrations
@@ -158,25 +158,22 @@ Cloud Spanner and PGAdapter do not support advisory locks. The advisory lock sta
 therefore be ignored and have no effect.
 
 ### Generated Primary Keys
-Generated primary keys are not supported and should be replaced with primary key definitions that
-are manually assigned. See https://cloud.google.com/spanner/docs/schema-design#primary-key-prevent-hotspots
-for more information on choosing a good primary key. This sample uses UUIDs that are generated by the
-application for primary keys.
+Generated primary keys are supported and use values that are not monotonically increasing. This
+prevents hotspots in your database. See https://cloud.google.com/spanner/docs/schema-design#primary-key-prevent-hotspots
+for more information. The `TicketSale` model in this sample uses an auto-generated primary key. The
+primary key is generated by a column with type `serial`, which uses a backing bit-reversed sequence
+to generate unique values.
 
 ```typescript
-model Singer {
-   id        String    @id
-   createdAt DateTime  @default(now())
-   updatedAt DateTime  @updatedAt
-   firstName String
-   lastName  String
-   /// `fullName` is generated by the database and should not be set.
-   fullName  String?
-   active    Boolean
-   albums    Album[]
-   Concert   Concert[]
-   
-   @@index(lastName)
+model TicketSale {
+   id           Int @id @default(autoincrement())
+   createdAt    DateTime @default(now())
+   updatedAt    DateTime @updatedAt
+   concert      Concert @relation(fields: [concertId], references: [id])
+   concertId    String
+   customerName String
+   price        Decimal
+   seats        String[]
 }
 ```
 
@@ -187,4 +184,4 @@ column for the `fullName` property of `Singer`. See [migration.sql](prisma/migra
 for an example.
 
 ### Upsert
-`Upsert` statements are not supported by Cloud Spanner and should not be used.
+`Upsert` statements are not supported by Spanner and should not be used.

samples/nodejs/prisma-sample-app/prisma/migrations/20250323192300_auto_generated_pk/migration.sql

@@ -0,0 +1,11 @@
+-- CreateTable
+CREATE TABLE "TicketSale" (
+    "id" SERIAL PRIMARY KEY,
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "updatedAt" TIMESTAMP(3) NOT NULL,
+    "concertId" TEXT NOT NULL,
+    "customerName" TEXT NOT NULL,
+    "price" NUMERIC,
+    "seats" TEXT[] NOT NULL,
+    CONSTRAINT "TicketSale_concertId_fkey" FOREIGN KEY ("concertId") REFERENCES "Concert"("id") ON DELETE RESTRICT ON UPDATE CASCADE
+);

samples/nodejs/prisma-sample-app/prisma/schema.prisma

@@ -57,15 +57,27 @@ model Venue {
 }
 
 model Concert {
-  id        String   @id
-  createdAt DateTime @default(now())
-  updatedAt DateTime @updatedAt
-  name      String
-  venue     Venue    @relation(fields: [venueId], references: [id])
-  venueId   String
-  singer    Singer   @relation(fields: [singerId], references: [id])
-  singerId  String
-  startTime DateTime @db.Timestamptz
-  endTime   DateTime @db.Timestamptz
+  id          String   @id
+  createdAt   DateTime @default(now())
+  updatedAt   DateTime @updatedAt
+  name        String
+  venue       Venue    @relation(fields: [venueId], references: [id])
+  venueId     String
+  singer      Singer   @relation(fields: [singerId], references: [id])
+  singerId    String
+  startTime   DateTime @db.Timestamptz
+  endTime     DateTime @db.Timestamptz
+  ticketSales TicketSale[]
   @@index([startTime(sort: Desc)])
 }
+
+model TicketSale {
+  id           Int @id @default(autoincrement())
+  createdAt    DateTime @default(now())
+  updatedAt    DateTime @updatedAt
+  concert      Concert @relation(fields: [concertId], references: [id])
+  concertId    String
+  customerName String
+  price        Decimal
+  seats        String[]
+}

samples/nodejs/prisma-sample-app/src/index.ts

@@ -14,7 +14,7 @@
 
 import {
   createPrismaClient,
-  createRandomSingersAndAlbumsAndTracks,
+  createRandomSingersAndAlbumsAndTracks, createTicketSale,
   createVenueAndConcertInTransaction,
   deleteExistingData, deployMigrations, printAlbumsReleasedBefore1900,
   printSingersAndAlbums, staleRead, updateVenueDescription
@@ -63,6 +63,7 @@ async function runSample() {
   await printAlbumsReleasedBefore1900();
   await updateVenueDescription();
   await staleRead();
+  await createTicketSale();
 
   // Run 'npx prisma migrate deploy' once more, just to verify that we can run this command multiple
   // times on an existing database.

samples/nodejs/prisma-sample-app/src/sample.ts

@@ -54,8 +54,12 @@ export async function deployMigrations() {
 }
 
 export async function deleteExistingData() {
+  console.log("Deleting all existing ticket sales");
+  let result = await prisma.ticketSale.deleteMany({});
+  console.log(`Deleted ${result.count} ticket sales`);
+  
   console.log("Deleting all existing concerts");
-  let result = await prisma.concert.deleteMany({});
+  result = await prisma.concert.deleteMany({});
   console.log(`Deleted ${result.count} concerts`);
 
   console.log("Deleting all existing albums and related tracks");
@@ -185,6 +189,21 @@ export async function createVenueAndConcertInTransaction() {
   console.log();
 }
 
+export async function createTicketSale() {
+  console.log("Creating a ticket sale. Ticket sale uses an auto-generated primary key");
+  const concert = await prisma.concert.findFirst({});
+  const ticketSale = await prisma.ticketSale.create({
+    data: {
+      concertId: concert.id,
+      customerName: "Alice Neeson",
+      price: 99.50,
+      seats: ["A11", "A12", "A13"],
+    }
+  });
+  console.log(`Created a ticket sale with id ${ticketSale.id}`);
+  console.log();
+}
+
 export async function printAlbumsReleasedBefore1900() {
   console.log("Searching for albums released before 1900");
   const albums = await prisma.album.findMany({