read replicas

README.md

@@ -160,6 +160,57 @@ generator kysely {
 
 Take a look at [the camel case example](examples/camel-case/) to see it in action! Check out the [Kysely documentation](https://kysely.dev/) for more information about plugins.
 
+## Read Replicas
+
+Using read replicas with `prisma-extension-kysely` is a breeze!
+Just use the excellent [`@prisma/extension-read-replicas`](https://www.npmjs.com/package/@prisma/extension-read-replicas) extension as normal.
+Pay attention to how it's configured, though:
+
+```typescript
+// Use a common config for primary and replica clients (or different configs)
+const kyselyExtensionArgs: PrismaKyselyExtensionArgs<DB> = {
+  kysely: (driver) =>
+    new Kysely<DB>({
+      dialect: {
+        createAdapter: () => new SqliteAdapter(),
+        createDriver: () => driver,
+        createIntrospector: (db) => new SqliteIntrospector(db),
+        createQueryCompiler: () => new SqliteQueryCompiler(),
+      },
+    }),
+};
+
+// Initialize the replica client(s) and add the Kysely extension
+const replicaClient = new PrismaClient({
+  datasourceUrl: "YOUR_REPLICA_URL", // Replace this with your replica's URL!
+  log: [{ level: "query", emit: "event" }],
+}).$extends(kyselyExtension(kyselyExtensionArgs));
+
+// Initialize the primary client and add the Kysely extension and the read replicas extension
+const prisma = new PrismaClient()
+  .$extends(kyselyExtension(kyselyExtensionArgs)) // Apply the Kysely extension before the read replicas extension!
+  .$extends(
+    readReplicas({
+      replicas: [replicaClient],
+    }),
+  ); // Apply the read replicas extension after the Kysely extension!
+```
+
+See how we're setting up the replica client as a fully-fledged Prisma client and extending it separately? That's the secret sauce!
+It make sure that the replica client has a separate Kysely instance. If you try to use bare URLs, you'll run into trouble;
+it'll share the same Kysely instance as the primary client, and you'll get unpleasant surprises!
+
+```typescript
+// Don't do this! It won't work as expected.
+readReplicas({
+  url: "postgresql://user:password@localhost:5432/dbname",
+});
+```
+
+Also, note that we're applying the Kysely extension before the read replicas extension. This is important! If you apply the read replicas extension first, you won't get `.$kysely` on the primary client.
+
+Check out the [read replicas example](examples/read-replicas/) for a runnable example!
+
 ## Examples
 
 Check out the [examples](examples) directory for a sample project!

examples/read-replica/.gitignore

@@ -0,0 +1,5 @@
+# Generated files
+prisma/generated
+
+# Prisma local database file
+prisma/dev.db

examples/read-replica/index.ts

@@ -0,0 +1,122 @@
+import { PrismaClient } from "@prisma/client";
+import {
+  Kysely,
+  SqliteAdapter,
+  SqliteIntrospector,
+  SqliteQueryCompiler,
+} from "kysely";
+import kyselyExtension, {
+  PrismaKyselyExtensionArgs,
+} from "prisma-extension-kysely";
+import type { DB } from "./prisma/generated/types.js";
+import { readReplicas } from "@prisma/extension-read-replicas";
+
+// Use a common config for primary and replica clients
+const kyselyExtensionArgs: PrismaKyselyExtensionArgs<DB> = {
+  kysely: (driver) =>
+    new Kysely<DB>({
+      dialect: {
+        createAdapter: () => new SqliteAdapter(),
+        createDriver: () => driver,
+        createIntrospector: (db) => new SqliteIntrospector(db),
+        createQueryCompiler: () => new SqliteQueryCompiler(),
+      },
+    }),
+};
+
+// Initialize the replica client(s) and add the Kysely extension
+const replicaClient = new PrismaClient({
+  // For demonstration purposes, use the same SQLite database
+  datasourceUrl: "file:./dev.db",
+  log: [{ level: "query", emit: "event" }],
+}).$extends(kyselyExtension(kyselyExtensionArgs));
+
+// Initialize the primary client and add the Kysely extension
+const prisma = new PrismaClient()
+  .$extends(kyselyExtension(kyselyExtensionArgs))
+  .$extends(
+    readReplicas({
+      replicas: [replicaClient],
+    }),
+  );
+
+async function main() {
+  console.log(
+    "Is prisma.$kysely the same as prisma.$primary().$kysely?",
+    prisma.$kysely === prisma.$primary().$kysely,
+  );
+  console.log(
+    "Is prisma.$kysely the same as prisma.$replica().$kysely?",
+    prisma.$kysely === prisma.$replica().$kysely,
+  );
+  console.log(
+    "Is prisma.$primary().$kysely the same as prisma.$replica().$kysely?",
+    prisma.$primary().$kysely === prisma.$replica().$kysely,
+  );
+
+  // Clear the database before running the example
+  const deletedPosts = await prisma.$kysely
+    .deleteFrom("Post")
+    .executeTakeFirstOrThrow();
+  console.log("Deleted posts:", Number(deletedPosts.numDeletedRows));
+  const deletedUsers = await prisma.$kysely
+    .deleteFrom("User")
+    .executeTakeFirstOrThrow();
+  console.log("Deleted users:", Number(deletedUsers.numDeletedRows));
+
+  // Create and update a user
+  const insertedUser = await prisma.$transaction(async (tx) => {
+    const [insertedUser] = await tx.$kysely
+      .insertInto("User")
+      .values({ name: "John", email: "[email protected]" })
+      .returningAll()
+      .execute();
+    const affectedRows = await tx.$kysely
+      .updateTable("User")
+      .set({ name: "John Doe" })
+      .where("id", "=", insertedUser.id)
+      .executeTakeFirstOrThrow();
+    console.log("Updated users:", Number(affectedRows.numUpdatedRows));
+
+    return insertedUser;
+  });
+
+  // Create a post
+  await prisma
+    .$primary()
+    .$kysely.insertInto("Post")
+    .values({
+      title: "Hello prisma!",
+      content: "This is my first post about prisma",
+      updatedAt: new Date().toISOString(),
+      published: 1,
+      authorId: insertedUser.id,
+    })
+    .returningAll()
+    .execute();
+
+  // Select a user and a post
+  const userQuery = prisma
+    .$replica()
+    .$kysely.selectFrom("User")
+    .selectAll()
+    .where("id", "=", insertedUser.id);
+  const user = await userQuery.executeTakeFirstOrThrow();
+
+  const postQuery = prisma
+    .$replica()
+    .$kysely.selectFrom("Post")
+    .selectAll()
+    .where((eb) =>
+      eb.or([
+        eb("title", "like", "%prisma%"),
+        eb("content", "like", "%prisma%"),
+      ]),
+    )
+    .where("published", "=", 1);
+  const post = await postQuery.executeTakeFirstOrThrow();
+
+  console.log("Query results:", { user, post });
+}
+
+main();