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Chris Cho
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DOCSP-19819: transactions (mongodb#271)
* DOCSP-19396: transactions
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‎source/code-snippets/transactions/txn-callback.js

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const { MongoClient } = require('mongodb');
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async function cleanUp(client) {
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try {
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const customersColl = client.db('testdb').collection('customers');
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await customersColl.drop();
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} catch(e) {}
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try {
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const inventoryColl = client.db('testdb').collection('inventory');
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await inventoryColl.drop();
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} catch(e) {}
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try {
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const ordersCollection = client.db('testdb').collection('orders')
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await ordersCollection.drop();
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} catch(e) {}
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}
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async function setup(client) {
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try {
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const customerColl = client.db('testdb').collection('customers');
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const inventoryColl = client.db('testdb').collection('inventory');
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await customerColl.insertOne({ _id: 98765, orders: [] });
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await inventoryColl.insertMany([
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{ name: 'sunblock', sku: 5432, qty: 85 },
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{ name: 'beach towel', sku: 7865, qty: 41 },
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]);
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} catch (e) {
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console.log('Unable to insert test data: ' + e);
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}
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}
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async function queryData() {
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const uri = process.env.MONGODB_URI;
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const client = new MongoClient(uri, { useUnifiedTopology: true });
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try {
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await client.connect();
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await Promise.all(['customers', 'inventory', 'orders'].map(async c => {
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const coll = client.db('testdb').collection(c);
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console.log(JSON.stringify(await coll.find().toArray()));
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}, client));
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} finally {
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client.close();
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}
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}
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// start callback
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async function placeOrder(client, session, cart, payment) {
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const ordersCollection = client.db('testdb').collection('orders');
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const orderResult = await ordersCollection.insertOne(
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{
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customer: payment.customer,
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items: cart,
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total: payment.total,
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},
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{ session }
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);
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const inventoryCollection = client.db('testdb').collection('inventory');
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for (let i=0; i<cart.length; i++) {
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const item = cart[i];
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// Cancel the transaction when you have insufficient inventory
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const checkInventory = await inventoryCollection.findOne(
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{
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sku: item.sku,
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qty: { $gte: item.qty }
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},
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{ session }
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);
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if (checkInventory === null) {
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await session.abortTransaction();
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console.error('Insufficient quantity or SKU not found.');
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}
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await inventoryCollection.updateOne(
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{ sku: item.sku },
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{ $inc: { 'qty': -item.qty }},
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{ session }
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);
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}
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const customerCollection = client.db('testdb').collection('customers');
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await customerCollection.updateOne(
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{ _id: payment.customer },
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{ $push: { orders: orderResult.insertedId }},
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{ session }
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);
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}
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// end callback
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const uri = process.env.MONGODB_URI;
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const client = new MongoClient(uri, { useUnifiedTopology: true });
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async function run() {
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/* Test code: uncomment block to run
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await client.connect();
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await cleanUp(client);
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await setup(client);
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const cart = [
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{ name: 'sunblock', sku: 5432, qty: 1, price: 5.19 },
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{ name: 'beach towel', sku: 7865, qty: 2, price: 15.99 }
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];
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const payment = { customer: 98765, total: 37.17 };
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const transactionOptions = {
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readPreference: 'primary',
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readConcern: { level: 'local' },
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writeConcern: { w: 'majority' },
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maxCommitTimeMS: 1000
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};
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const session = client.startSession();
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try {
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await session.withTransaction(async () => {
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await placeOrder(client, session, cart, payment)
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}, transactionOptions);
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} catch(error) {
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console.log('Encountered an error during the transaction: ' + error);
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} finally {
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await session.endSession();
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}
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await client.close();
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*/
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// start session
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const transactionOptions = {
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readPreference: 'primary',
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readConcern: { level: 'local' },
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writeConcern: { w: 'majority' },
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maxCommitTimeMS: 1000
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};
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const session = client.startSession();
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try {
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await session.withTransaction(
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async (session) => { /* your transaction here */ },
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transactionOptions);
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} catch(error) {
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console.log('Encountered an error during the transaction: ' + error);
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} finally {
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await session.endSession();
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}
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// end session
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}
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run().then(() => queryData());

‎source/code-snippets/transactions/txn-core.js

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const { MongoError, MongoClient } = require('mongodb');
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// drop collections
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async function cleanUp(client) {
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await Promise.all( ['customers', 'inventory', 'orders'].map(async c => {
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try {
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const coll = client.db('testdb').collection(c);
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await coll.drop();
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} catch(e) {}
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}));
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}
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async function setup(client) {
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try {
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const customerColl = client.db('testdb').collection('customers');
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const inventoryColl = client.db('testdb').collection('inventory');
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await customerColl.insertOne({ _id: 98765, orders: [] });
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await inventoryColl.insertMany([
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{ name: 'sunblock', sku: 5432, qty: 85 },
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{ name: 'beach towel', sku: 7865, qty: 41 },
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]);
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} catch (e) {
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console.log('Unable to insert test data: ' + e);
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}
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}
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async function queryData() {
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const uri = process.env.MONGODB_URI;
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const client = new MongoClient(uri, { useUnifiedTopology: true });
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try {
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await client.connect();
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await Promise.all(['customers', 'inventory', 'orders'].map(async c => {
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const coll = client.db('testdb').collection(c);
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console.log(JSON.stringify(await coll.find().toArray()));
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}, client));
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} finally {
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client.close();
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}
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}
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// start placeOrder
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async function placeOrder(client, cart, payment) {
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const transactionOptions = {
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readConcern: { level: 'snapshot' },
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writeConcern: { w: 'majority' },
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readPreference: 'primary'
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};
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const session = client.startSession();
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try {
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session.startTransaction(transactionOptions);
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const ordersCollection = client.db('testdb').collection('orders');
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const orderResult = await ordersCollection.insertOne(
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{
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customer: payment.customer,
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items: cart,
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total: payment.total,
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},
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{ session }
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);
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const inventoryCollection = client.db('testdb').collection('inventory');
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for (let i=0; i<cart.length; i++) {
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const item = cart[i];
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// Cancel the transaction when you have insufficient inventory
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const checkInventory = await inventoryCollection.findOne(
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{
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sku: item.sku,
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qty: { $gte: item.qty }
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},
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{ session }
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)
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if (checkInventory === null) {
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throw new Error('Insufficient quantity or SKU not found.');
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}
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await inventoryCollection.updateOne(
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{ sku: item.sku },
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{ $inc: { 'qty': -item.qty }},
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{ session }
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);
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}
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const customerCollection = client.db('testdb').collection('customers');
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await customerCollection.updateOne(
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{ _id: payment.customer },
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{ $push: { orders: orderResult.insertedId }},
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{ session }
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);
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await session.commitTransaction();
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console.log('Transaction successfully committed.');
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} catch (error) {
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if (error instanceof MongoError && error.hasErrorLabel('UnknownTransactionCommitResult')) {
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// add your logic to retry or handle the error
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}
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else if (error instanceof MongoError && error.hasErrorLabel('TransientTransactionError')) {
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// add your logic to retry or handle the error
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} else {
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console.log('An error occured in the transaction, performing a data rollback:' + error);
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}
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await session.abortTransaction();
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} finally {
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await session.endSession();
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}
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}
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// end placeOrder
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async function run() {
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const uri = process.env.MONGODB_URI;
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const client = new MongoClient(uri, { useNewUrlParser: true, useUnifiedTopology: true });
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await client.connect();
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await cleanUp(client);
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await setup(client);
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const cart = [
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{ name: 'sunblock', sku: 5432, qty: 1, price: 5.19 },
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{ name: 'beach towel', sku: 7865, qty: 2, price: 15.99 }
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];
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const payment = { customer: 98765, total: 37.17 };
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try {
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await placeOrder(client, cart, payment);
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} finally {
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await cleanUp(client);
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await client.close();
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}
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}
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run().then(() => queryData());

‎source/fundamentals.txt

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/fundamentals/crud
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/fundamentals/promises
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/fundamentals/aggregation
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/fundamentals/transactions
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/fundamentals/indexes
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/fundamentals/collations
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/fundamentals/logging

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