public async Task PlaceOrder()
{
// Generate unique ID which will be persisted in this routine.
var transationId = Guid.NewGuid();
var price = 10;
var itemId = "Whole Coffee Beans 1lb";
var quantity = 1;
// !!! LOOK HERE !!!
// This is implementation of the Saga Pattern.
// Remember, any step will be re-tried if the process fails abruptly.
// 1. First, make sure that payment can be made.
// This is a call to a service #1.
await _paymentProcessor.Credit(transationId, price);
try
{
// 2. Then, reserve the item being purchased.
// This is a call to a service #2.
await _warehouse.ReserveItem(transationId, itemId, quantity);
// 3. Well, they are out of stock.
// The OutOfStockException is thrown.
}
catch
{
// 4. Refund the cost of an item.
// Perform a compensating action on service #1.
await _paymentProcessor.Debit(transationId, price);
}
// All in all, this async method (a routine) acts as an orchestrator.
// Invoking and subscribing to continuations of async methods of two
// services can be viewed as sending commands and listening to events.
}
// The simplified saga implementation in one method (orchestration).
public virtual async Task PlaceOrder()
{
// Generate unique ID which will be persisted in this method.
var transationId = Guid.NewGuid();
var price = 10;
var itemId = "Whole Coffee Beans 1lb";
var quantity = 1;
// 1. First, make sure that payment can be made.
// This is a call to a service #1.
await _paymentProcessor.Credit(transationId, price);
try
{
// 2. Then, reserve the item being purchased.
// This is a call to a service #2.
await _warehouse.ReserveItem(transationId, itemId, quantity);
// 3. Well, they are out of stock.
// The OutOfStockException is thrown.
}
catch
{
// 4. Refund the cost of an item.
// Perform a compensating action on service #1.
await _paymentProcessor.Debit(transationId, price);
}
// All in all, this async method (a routine) acts as an orchestrator.
// Invoking and subscribing to continuations of async methods of two
// services can be viewed as sending commands and listening to events.
// Unlike using regular synchronous service client (e.g. http), this
// method is guaranteed to reliably execute when message passing is used.
}