Creating MongoDB Transactions in C# Applications

Review the following code, which demonstrates how to create a multi-document transaction in MongoDB with C#.

Multi-Document Transaction

The following are the steps and the code to create a multi-document transaction in MongoDB with C#. The transaction is started by using the session’s WithTransaction() method. Then, we define the sequence of operations to perform inside the transaction. Here are the steps:

1. Start a new session.
2. Begin a transaction with the WithTransaction() method on the session.
3. Create variables that will be used in the transaction.
4. Obtain the user accounts information that will be used in the transaction.
5. Create the transfer document.
6. Update the user accounts.
7. Insert the transfer document.
8. Commit the transaction.

Here's the code:

using (var session = client.StartSession())
{

    // Define the sequence of operations to perform inside the transactions
    session.WithTransaction(
        (s, ct) =>
        {
            var fromId = "MDB310054629";
            var toId = "MDB546986470";

            // Create the transfer_id and amount being transfered
            var transferId = "TR02081994";
            var transferAmount = 20;

            // Obtain the account that the money will be coming from
            var fromAccountResult = accountsCollection.Find(e => e.AccountId == fromId).FirstOrDefault();
            // Get the balance and id of the account that the money will be coming from
            var fromAccountBalance = fromAccountResult.Balance - transferAmount;
            var fromAccountId = fromAccountResult.AccountId;

            Console.WriteLine(fromAccountBalance.GetType());

            // Obtain the account that the money will be going to
            var toAccountResult = accountsCollection.Find(e => e.AccountId == toId).FirstOrDefault();
            // Get the balance and id of the account that the money will be going to
            var toAccountBalance = toAccountResult.Balance + transferAmount;
            var toAccountId = toAccountResult.AccountId;

            // Create the transfer record
            var transferDocument = new Transfers
            {
                TransferId = transferId,
                ToAccount = toAccountId,
                FromAccount = fromAccountId,
                Amount = transferAmount
            };

            // Update the balance and transfer array for each account
            var fromAccountUpdateBalance = Builders<Accounts>.Update.Set("balance", fromAccountBalance);
            var fromAccountFilter = Builders<Accounts>.Filter.Eq("account_id", fromId);
            accountsCollection.UpdateOne(fromAccountFilter, fromAccountUpdateBalance);

            var fromAccountUpdateTransfers = Builders<Accounts>.Update.Push("transfers_complete", transferId);
            accountsCollection.UpdateOne(fromAccountFilter, fromAccountUpdateTransfers);

            var toAccountUpdateBalance = Builders<Accounts>.Update.Set("balance", toAccountBalance);
            var toAccountFilter = Builders<Accounts>.Filter.Eq("account_id", toId);
            accountsCollection.UpdateOne(toAccountFilter, toAccountUpdateBalance);
            var toAccountUpdateTransfers = Builders<Accounts>.Update.Push("transfers_complete", transferId);

            // Insert transfer doc
            transfersCollection.InsertOne(transferDocument);
            Console.WriteLine("Transaction complete!");
            return "Inserted into collections in different databases";
        });
}