Create Multi-Document Transactions in MongoDB for Node.js Applications

A multi-document transaction is a group of database operations that will be completed together as a unit or not at all. They are used when a group of related operations must either all succeed or fail together, which is a property called atomicity.

Let's go through the code to create a transaction step by step: We start the transaction by using the session’s withTransaction() method. We then define the sequence of operations to perform inside the transactions, passing the session object to each operation in the transactions.

1. Create variables used in the transaction.

    // Collections
    const accounts = client.db("bank").collection("accounts")
    const transfers = client.db("bank").collection("transfers")
   
    // Account information
    let account_id_sender = "MDB574189300"
    let account_id_receiver = "MDB343652528"
    let transaction_amount = 100
   

2. Start a new session.

    const session = client.startSession()
   

3. Begin a transaction with the WithTransaction() method on the session.

    const transactionResults = await session.withTransaction(async () => {
      // Operations (Step 4 - 8) will go here
    })
   

4. Update the balance field of the sender’s account by decrementing the transaction_amount from the balance field.

    const senderUpdate = await accounts.updateOne(
      { account_id: account_id_sender },
      { $inc: { balance: -transaction_amount } },
      { session }
    )
   

   Update the balance field of the receiver’s account by incrementing the transaction_amount to the balance field.

    const receiverUpdate = await accounts.updateOne(
      { account_id: account_id_receiver },
      { $inc: { balance: transaction_amount } },
      { session }
    )
   

5. Create a transfer document and insert it into the transfers collection.

    const transfer = {
      transfer_id: "TR21872187",
      amount: 100,
      from_account: account_id_sender,
      to_account: account_id_receiver,
    }
   
    const insertTransferResults = await transfers.insertOne(transfer, { session })
   

6. Update the transfers_complete array of the sender’s account by adding the transfer_id to the array.

    const updateSenderTransferResults = await accounts.updateOne(
      { account_id: account_id_sender },
      { $push: { transfers_complete: transfer.transfer_id } },
      { session }
    )
   

   Update the transfers_complete array of the receiver’s account by adding the transfer_id to the array.

    const updateReceiverTransferResults = await accounts.updateOne(
      { account_id: account_id_receiver },
      { $push: { transfers_complete: transfer.transfer_id } },
      { session }
    )
   

7. Log a message regarding the success or failure of the transaction.

    if (transactionResults) {
      console.log("Transaction completed successfully.")
    } else {
      console.log("Transaction failed.")
    }
   

8. Catch any errors and close the session.

    catch (err) {
      console.error(`Transaction aborted: ${err}`)
      process.exit(1)
    } finally {
      await session.endSession()
      await client.close()
    }
   

By default, a multi-document transaction has a 60-second time limit. This means that MongoDB will automatically cancel any multi-document transaction that runs for more than 60 seconds.