# Simple Cosmos DB Persistence Usage


This sample shows a client/server scenario using non-transactional saga persistence.

## Prerequisites

Ensure that an instance of the latest [Azure Cosmos DB Emulator](https://learn.microsoft.com/en-us/azure/cosmos-db/local-emulator) is running.

## Sample structure

This sample contains three projects, `SharedMessages`, `Client` and `Server`.

### SharedMessages

The shared message contracts used by all endpoints.

### Client

* Sends the `StartOrder` message to `Server`.
* Receives and handles the `OrderCompleted` event.

### Server

* Receive the `StartOrder` message and initiate an `OrderSaga`.
* `OrderSaga` requests a timeout with an instance of `CompleteOrder` with the saga data.
* `OrderSaga` publishes an `OrderCompleted` event when the `CompleteOrder` timeout fires.

## Implementation highlights

### Persistence config

In Program.cs of the Server project, the endpoint is configured to use Cosmos DB Persistence:

<!-- snippet: CosmosDBConfig -->

```cs
var endpointConfiguration = new EndpointConfiguration("Samples.CosmosDB.Simple.Server");

var persistence = endpointConfiguration.UsePersistence<CosmosPersistence>();
var connection = Environment.GetEnvironmentVariable("COSMOS_CONNECTION_STRING")
    ?? """AccountEndpoint=https://localhost:8081/;AccountKey=C2y6yDjf5/R+ob0N8A7Cgv30VRDJIWEHLM+4QDU5DE2nQ9nDuVTqobD4b8mGGyPMbIZnqyMsEcaGQy67XIw/Jw==""";
persistence.DatabaseName("Samples.CosmosDB.Simple");
persistence.CosmosClient(new(connection));
persistence.DefaultContainer("Server", "/id");
```

<!-- endsnippet -->

In the non-transactional mode, the saga id is used as a partition key, and thus, the container needs to use `/id` as the partition key path.

## Order saga data

The data stored on the saga is defined on the `OrderSagaData.cs` file inside the `Server` project:

<!-- snippet: sagadata -->

```cs
public class OrderSagaData :
    ContainSagaData
{
    public Guid OrderId { get; set; }
    public string OrderDescription { get; set; }
}
```

<!-- endsnippet -->

## Order saga

The handler for this data is on the `OrderSaga.cs` file on the `Server` project:

<!-- snippet: thesaga -->

```cs
public class OrderSaga(ILogger<OrderSaga> logger) :
    Saga<OrderSagaData>,
    IAmStartedByMessages<StartOrder>,
    IHandleTimeouts<CompleteOrder>
{

    protected override void ConfigureHowToFindSaga(SagaPropertyMapper<OrderSagaData> mapper)
    {
        mapper.MapSaga(saga => saga.OrderId).ToMessage<StartOrder>(msg => msg.OrderId);
    }

    public Task Handle(StartOrder message, IMessageHandlerContext context)
    {
        var orderDescription = $"The saga for order {message.OrderId}";
        Data.OrderDescription = orderDescription;
        logger.LogInformation($"Received StartOrder message {Data.OrderId}. Starting Saga");

        var shipOrder = new ShipOrder
        {
            OrderId = message.OrderId
        };

        logger.LogInformation("Order will complete in 5 seconds");
        CompleteOrder timeoutData = new()
        {
            OrderDescription = orderDescription,
        };

        return Task.WhenAll([
            context.SendLocal(shipOrder),
            RequestTimeout(context, TimeSpan.FromSeconds(5), timeoutData)
        ]);
    }

    public Task Timeout(CompleteOrder state, IMessageHandlerContext context)
    {
        logger.LogInformation($"Saga with OrderId {Data.OrderId} completed");
        MarkAsComplete();
        OrderCompleted orderCompleted = new()
        {
            OrderId = Data.OrderId
        };
        return context.Publish(orderCompleted);
    }
}
```

<!-- endsnippet -->