Transactions

{ _id: 98765, orders: [] }

[
 { name: "sunblock", sku: 5432, qty: 85 },
 { name: "beach towel", sku: 7865, qty: 41 }
]

const cart = [
  { name: 'sunblock', sku: 5432, qty: 1, price: 5.19 },
  { name: 'beach towel', sku: 7865, qty: 2, price: 15.99 }
];
const payment = { customer: 98765, total: 37.17 };

1
async function placeOrder(client, cart, payment) {
2
  const transactionOptions = {
3
    readConcern: { level: 'snapshot' },
4
    writeConcern: { w: 'majority' },
5
    readPreference: 'primary'
6
  };
7
8
  const session = client.startSession();
9
  try {
10
    session.startTransaction(transactionOptions);
11
12
    const ordersCollection = client.db('testdb').collection('orders');
13
    const orderResult = await ordersCollection.insertOne(
14
      {
15
        customer: payment.customer,
16
        items: cart,
17
        total: payment.total,
18
      },
19
      { session }
20
    );
21
22
    const inventoryCollection = client.db('testdb').collection('inventory');
23
    for (let i=0; i<cart.length; i++) {
24
      const item = cart[i];
25
26
      // Cancel the transaction when you have insufficient inventory
27
      const checkInventory = await inventoryCollection.findOne(
28
        {
29
          sku: item.sku,
30
          qty: { $gte: item.qty }
31
        },
32
        { session }
33
      )
34
      if (checkInventory === null) {
35
        throw new Error('Insufficient quantity or SKU not found.');
36
      }
37
38
      await inventoryCollection.updateOne(
39
        { sku: item.sku },
40
        { $inc: { 'qty': -item.qty }},
41
        { session }
42
      );
43
    }
44
45
    const customerCollection = client.db('testdb').collection('customers');
46
    await customerCollection.updateOne(
47
      { _id: payment.customer },
48
      { $push:  { orders: orderResult.insertedId }},
49
      { session }
50
    );
51
    await session.commitTransaction();
52
    console.log('Transaction successfully committed.');
53
54
  } catch (error) {
55
    if (error instanceof MongoError && error.hasErrorLabel('UnknownTransactionCommitResult')) {
56
      // add your logic to retry or handle the error
57
    }
58
    else if (error instanceof MongoError && error.hasErrorLabel('TransientTransactionError')) {
59
      // add your logic to retry or handle the error
60
    } else {
61
      console.log('An error occured in the transaction, performing a data rollback:' + error);
62
    }
63
    await session.abortTransaction();
64
  } finally {
65
    await session.endSession();
66
  }
67
}

const { MongoError, MongoClient } = require('mongodb');

1
const transactionOptions = {
2
  readPreference: 'primary',
3
  readConcern: { level: 'local' },
4
  writeConcern: { w: 'majority' },
5
  maxCommitTimeMS: 1000
6
};
7
8
const session = client.startSession();
9
try {
10
  await session.withTransaction(
11
    async (session) => { /* your transaction here */ },
12
    transactionOptions);
13
} catch(error) {
14
  console.log('Encountered an error during the transaction: ' + error);
15
} finally {
16
  await session.endSession();
17
}

1
async function placeOrder(client, session, cart, payment) {
2
  const ordersCollection = client.db('testdb').collection('orders');
3
  const orderResult = await ordersCollection.insertOne(
4
    {
5
      customer: payment.customer,
6
      items: cart,
7
      total: payment.total,
8
    },
9
    { session }
10
  );
11
12
  const inventoryCollection = client.db('testdb').collection('inventory');
13
  for (let i=0; i<cart.length; i++) {
14
    const item = cart[i];
15
16
    // Cancel the transaction when you have insufficient inventory
17
    const checkInventory = await inventoryCollection.findOne(
18
      {
19
        sku: item.sku,
20
        qty: { $gte: item.qty }
21
      },
22
      { session }
23
    );
24
25
    if (checkInventory === null) {
26
      await session.abortTransaction();
27
      console.error('Insufficient quantity or SKU not found.');
28
    }
29
30
    await inventoryCollection.updateOne(
31
      { sku: item.sku },
32
      { $inc: { 'qty': -item.qty }},
33
      { session }
34
    );
35
  }
36
37
  const customerCollection = client.db('testdb').collection('customers');
38
  await customerCollection.updateOne(
39
    { _id: payment.customer },
40
    { $push:  { orders: orderResult.insertedId }},
41
    { session }
42
  );
43
}