Add transactions inventory example

transaction-inventoryexample.js

@@ -0,0 +1,127 @@
+const { MongoClient } = require('mongodb');
+
+// In MongoDB 4.2 and earlier, CRUD operations in transactions must be on existing collections 
+// See https://docs.mongodb.com/manual/core/transactions/#transactions-api for more information
+
+// Before running this script...
+//   1. Create a database named 'book-store'
+//   2. Create a collection named 'orders' in the database
+//   3. Create a collection named 'inventory' in the database
+//   3. Create a document in the 'inventory' collection:
+//         { "_id": "parks-rec-book", "name": "The Ultimate Parks and Rec Book for the Ultimate Fans", "numberInStock": 5 }
+//   4: Optional: Add schema validation to the 'inventory' collection to ensure the number of items in stock cannot drop below 0.
+//      See https://docs.mongodb.com/manual/core/schema-validation/ for details on how to 
+//      enable schema validation. Configuring schema validation in MongoDB Compass is an
+//      easy way to add schema validation to an existing database: https://docs.mongodb.com/compass/current/validation/
+//
+//      {
+//        $jsonSchema: {
+//          properties: {
+//            numberInStock: {
+//              minimum: 0,
+//              description: 'numberInStock cannot be negative'
+//            }
+//          }
+//        }
+//      }
+
+async function main() {
+    /**
+     * Connection URI. Update <username>, <password>, and <your-cluster-url> to reflect your cluster.
+     * See https://docs.mongodb.com/drivers/node/ for more details
+     */
+    const uri = "mongodb+srv://<username>:<password>@<your-cluster-url>/book-store?retryWrites=true&w=majority";
+
+    /**
+     * The Mongo Client you will use to interact with your database
+     * See https://mongodb.github.io/node-mongodb-native/3.6/api/MongoClient.html for more details
+     */
+    const client = new MongoClient(uri);
+
+    try {
+        // Connect to the MongoDB cluster
+        await client.connect();
+
+        // User1 purchases 1 copy of parks-rec-book
+        await purchaseBook(client, "User1", "parks-rec-book", 1, "paid");
+
+    } finally {
+        // Close the connection to the MongoDB cluster
+        await client.close();
+    }
+}
+
+main().catch(console.error);
+
+/**
+ * Purchase a book
+ * @param {MongoClient} client A MongoClient that is connected to a cluster with the book-store database
+ * @param {String} userId The _id of the user who is purchasing the book
+ * @param {String} bookId The _id of the book being purchased
+ * @param {Number} quantity The number of copies being purchased
+ * @param {String} status The order status
+ */
+async function purchaseBook(client, userId, bookId, quantity, status) {
+
+    /**
+     * The orders collection in the book-store database
+     */
+    const ordersCollection = client.db("book-store").collection("orders");
+
+    /**
+     * The inventory collection in the book-store database
+     */
+     const inventoryCollection = client.db("book-store").collection("inventory");
+
+    // Step 1: Start a Client Session
+    // See https://mongodb.github.io/node-mongodb-native/3.6/api/MongoClient.html#startSession for the startSession() docs
+    const session = client.startSession();
+
+    // Step 2: Optional. Define options for the transaction
+    const transactionOptions = {
+        readPreference: 'primary',
+        readConcern: { level: 'local' },
+        writeConcern: { w: 'majority' }
+    };
+
+    try {
+        // Step 3: Use withTransaction to start a transaction, execute the callback, and commit (or abort on error)
+        // Note: The callback for withTransaction MUST be async and/or return a Promise.
+        // See https://mongodb.github.io/node-mongodb-native/3.6/api/ClientSession.html#withTransaction for the withTransaction() docs        
+        const transactionResults = await session.withTransaction(async () => {
+
+            // Important:: You must pass the session to each of the operations   
+
+            // Update the inventory to reflect the book has been sold
+            const updateInventoryResults = await inventoryCollection.updateOne(
+                { _id: bookId },
+                { $inc: { numberInStock: quantity * -1 } },
+                { session });
+            console.log(`${updateInventoryResults.matchedCount} document(s) found in the inventory collection with _id ${bookId}.`);
+            console.log(`${updateInventoryResults.modifiedCount} document(s) was/were updated.`);
+            if (updateInventoryResults.modifiedCount !== 1) {
+                await session.abortTransaction();
+                return;
+            }
+
+            // Record the order in the orders collection
+            const insertOrderResults = await ordersCollection.insertOne(
+                { "userId": userId , bookId: bookId, quantity: quantity, status: status },
+                { session });
+            console.log(`New order recorded with the following id: ${insertOrderResults.insertedId}`);
+
+        }, transactionOptions);
+
+        if (transactionResults) {
+            console.log("The order was successfully processed. Database operations from the transaction are now visible outside the transaction.");
+        } else {
+            console.log("The order was not successful. The transaction was intentionally aborted.");
+        }
+    } catch (e) {
+        console.log("The order was not successful. The transaction was aborted due to an unexpected error: " + e);
+    } finally {
+        // Step 4: End the session
+        await session.endSession();
+    }
+
+}