# NHibernate Custom Saga Finding Logic



## Code walk-through

When the default Saga message mappings do not satisfy the requirements, custom logic can be put in place to allow NServiceBus to find a saga data instance based on logic that best suits the environment.


## Prerequisites

Ensure an instance of SQL Server (Version 2016 or above for custom saga finders sample, or Version 2012 or above for other samples) is installed and accessible on `localhost` and port `1433`. A Docker image can be used to accomplish this by running `docker run --name mssql -e "ACCEPT_EULA=Y" -e "MSSQL_SA_PASSWORD=yourStrong(!)Password" -p 1433:1433 -d mcr.microsoft.com/mssql/server:latest` in a terminal.

Alternatively, change the connection string to point to different SQL Server instance.

At startup each endpoint will create its required SQL assets including databases, tables, and schemas.


This sample creates a database named `NsbSamplesNhCustomSagaFinder`.

### NHibernate setup

This sample uses the [NHibernate persistence](/persistence/nhibernate/index.md), configured as follows:

<!-- snippet: config -->

```cs
// for SqlExpress use Data Source=.\SqlExpress;Initial Catalog=NsbSamplesNhCustomSagaFinder;Integrated Security=True;Max Pool Size=100;Encrypt=false
var connectionString = @"Server=localhost,1433;Initial Catalog=NsbSamplesNhCustomSagaFinder;User Id=SA;Password=yourStrong(!)Password;Max Pool Size=100;Encrypt=false";
var hibernateConfig = new Configuration();
hibernateConfig.DataBaseIntegration(x =>
{
    x.ConnectionString = connectionString;
    x.Dialect<MsSql2012Dialect>();
    x.Driver<MicrosoftDataSqlClientDriver>();
});

var persistence = endpointConfiguration.UsePersistence<NHibernatePersistence>()
    .UseConfiguration(hibernateConfig);
```

<!-- endsnippet -->


## The Saga

This sample contains a very simple order management saga with these responsibilities:

- Handling the creation of an order.
- Offloading the payment process to a another handler.
- Handling the completion of the payment process.
- Completing the order.

<!-- snippet: saga -->

```cs
using Microsoft.Extensions.Logging;

public class OrderSaga(ILogger<OrderSaga> logger) :
    Saga<OrderSagaData>,
    IAmStartedByMessages<StartOrder>,
    IHandleMessages<CompletePaymentTransaction>,
    IHandleMessages<CompleteOrder>
{
    protected override void ConfigureHowToFindSaga(SagaPropertyMapper<OrderSagaData> mapper)
    {
        mapper.MapSaga(saga => saga.OrderId)
            .ToMessage<StartOrder>(msg => msg.OrderId)
            .ToMessage<CompleteOrder>(msg => msg.OrderId);

        mapper.ConfigureFinderMapping<CompletePaymentTransaction, CompletePaymentTransactionSagaFinder>();
    }

    public Task Handle(StartOrder message, IMessageHandlerContext context)
    {
        Data.PaymentTransactionId = Guid.NewGuid().ToString();

        logger.LogInformation("Saga with OrderId {SagaOrderId} received StartOrder with OrderId {MessageOrderId}", Data.OrderId, message.OrderId);
        var issuePaymentRequest = new IssuePaymentRequest
        {
            PaymentTransactionId = Data.PaymentTransactionId
        };
        return context.SendLocal(issuePaymentRequest);
    }

    public Task Handle(CompletePaymentTransaction message, IMessageHandlerContext context)
    {
        logger.LogInformation("Transaction with Id {PaymentTransactionId} completed for order id {OrderId}", Data.PaymentTransactionId, Data.OrderId);
        var completeOrder = new CompleteOrder
        {
            OrderId = Data.OrderId
        };
        return context.SendLocal(completeOrder);
    }

    public Task Handle(CompleteOrder message, IMessageHandlerContext context)
    {
        logger.LogInformation("Saga with OrderId {SagaOrderId} received CompleteOrder with OrderId {MessageOrderId}", Data.OrderId, message.OrderId);
        MarkAsComplete();
        return Task.CompletedTask;
    }
}
```

<!-- endsnippet -->

It is important to note that the saga is not sending the order ID to the payment processor. Instead, it is sending a payment transaction ID. This saga needs to be correlated by more than one property. For example, `OrderId` and `PaymentTransactionId`. This requires both of these properties to be treated as unique.


<!-- snippet: finder -->

```cs
class CompletePaymentTransactionSagaFinder : ISagaFinder<OrderSagaData, CompletePaymentTransaction>
{
    public Task<OrderSagaData> FindBy(CompletePaymentTransaction message, ISynchronizedStorageSession storageSession, IReadOnlyContextBag context, CancellationToken cancellationToken = default)
    {
        var session = storageSession.Session();
        var orderSagaData = session.QueryOver<OrderSagaData>()
            .Where(d => d.PaymentTransactionId == message.PaymentTransactionId)
            .SingleOrDefault();
        return Task.FromResult(orderSagaData);
    }
}
```

<!-- endsnippet -->

A saga finder is a class that implements `IFindSagas<TSagaData>.Using<TMessage>`. The class will be detected automatically by NServiceBus at endpoint configuration time. The `FindBy` method will be invoked by NServiceBus each time a message of type `TMessage` is received by a saga which stores its state using an instance of the `TSagaData` type.