Made the session optional for database with replica set not configured.

src/db.ts

@@ -1,6 +1,7 @@
 import mongoose from "mongoose";
 import { MONGO_DB_URL } from "./constants";
 import { logger } from "./libraries";
+import { checkReplicaSet } from "./utilities/checkReplicaSet";
 
 let session!: mongoose.ClientSession;
 
@@ -12,7 +13,14 @@ export const connect = async (): Promise<void> => {
       useFindAndModify: false,
       useNewUrlParser: true,
     });
-    session = await mongoose.startSession();
+
+    const replicaSet = await checkReplicaSet();
+    if (replicaSet) {
+      logger.info("Session started --> Connected to a replica set!");
+      session = await mongoose.startSession();
+    } else {
+      logger.info("Session not started --> Not Connected to a replica set!");
+    }
   } catch (error: unknown) {
     if (error instanceof Error) {
       const errorMessage = error.toString();

src/utilities/checkReplicaSet.ts

@@ -0,0 +1,20 @@
+import mongoose from "mongoose";
+import { logger } from "../libraries";
+
+export const checkReplicaSet = async (): Promise<boolean> => {
+  try {
+    const adminDb = mongoose.connection.db.admin();
+    const result = await adminDb.command({
+      hello: 1,
+    });
+
+    if ("hosts" in result) {
+      return true;
+    } else {
+      return false;
+    }
+  } catch (error) {
+    logger.error("Error checking replica set configuration :", error);
+    return false;
+  }
+};

tests/utilities/checkReplicaSet.spec.ts

@@ -0,0 +1,48 @@
+import mongoose from "mongoose";
+import { checkReplicaSet } from "../../src/utilities/checkReplicaSet";
+import { expect, describe, it, beforeAll, afterAll } from "vitest";
+import { connect, disconnect } from "../helpers/db";
+
+let MONGOOSE_INSTANCE: typeof mongoose;
+
+beforeAll(async (): Promise<void> => {
+  MONGOOSE_INSTANCE = await connect();
+});
+
+afterAll(async (): Promise<void> => {
+  await disconnect(MONGOOSE_INSTANCE);
+});
+
+interface InterfaceAdminDbMock1 {
+  command: () => Promise<{ hosts: string[] }>;
+}
+interface InterfaceAdminDbMock2 {
+  command: () => Promise<object>;
+}
+
+describe("checkReplicaSet", () => {
+  it("should return true if replica set is configured", async () => {
+    const adminDbMock: InterfaceAdminDbMock1 = {
+      command: async (): Promise<{ hosts: string[] }> => ({
+        hosts: ["host1", "host2"],
+      }),
+    };
+    //@ts-expect-error cant find the right type
+    mongoose.connection.db.admin = (): object => adminDbMock;
+    const result = await checkReplicaSet();
+
+    expect(result).toBe(true);
+  });
+
+  it("should return false if replica set is not configured", async () => {
+    const adminDbMock: InterfaceAdminDbMock2 = {
+      command: async (): Promise<object> => ({}),
+    };
+    //@ts-expect-error cant find the right type
+    mongoose.connection.db.admin = (): object => adminDbMock;
+
+    const result = await checkReplicaSet();
+
+    expect(result).toBe(false);
+  });
+});