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Tutorial2/5

2. The model and the Deserializer

Define the order message and implement the Deserializer.

Define the message

Section titled “Define the message”

The send pipeline receives bytes, then works on a typed message. Replace In and the placeholder comment in Line.cs:

src/Model/In.cs
namespace OrderSync.Model;


public record In(
    string OrderId,
    string CustomerId,
    DateTimeOffset OrderDate,
    IReadOnlyList<Line> Lines);
src/Model/Line.cs
namespace OrderSync.Model;


public record Line(
    string Sku,
    int Quantity,
    decimal UnitPrice);

Leave Out empty until chapter 3.

Implement the Deserializer

Section titled “Implement the Deserializer”

Keep the existing ExecuteAsync signature. Replace only its body, from the opening { to the closing }:

src/Send/Deserializer.cs: ExecuteAsync body
{
    var order = JsonSerializer.Deserialize<In>(input.Span,
        new JsonSerializerOptions { PropertyNameCaseInsensitive = true })!;


    context.Metadata[Constants.ContextKeyOrderId] = order.OrderId;
    context.Metadata[Constants.ContextKeyProcessedAt] = DateTimeOffset.UtcNow.ToString("O");


    return Task.FromResult<(BusinessStepResult<In>, Context)>(
        (new BusinessStepResult<In>.Success(order), context));
}

Store two context values:

  • ProcessedAt, read from the clock once.
  • OrderId, so later steps can name the order without re-parsing.

The metadata keys live in src/Configuration/Constants.cs.

Check it

Section titled “Check it”

Replace the skipped placeholder in test/OrderSync.Test.Unit/Send/DeserializerTests.cs:

test/OrderSync.Test.Unit/Send/DeserializerTests.cs
[Fact]
public async Task ExecuteAsync_WithValidJson_ReturnsSuccess()
{
    var deserializer = new Deserializer();
    var context = new Context(new Dictionary<string, string>());
    var json = """{"orderId":"ORD-1001","customerId":"CUST-42","orderDate":"2026-01-15T09:30:00+00:00","lines":[{"sku":"SKU-1","quantity":2,"unitPrice":10.0}]}""";


    var (result, _) = await deserializer.ExecuteAsync(
        Encoding.UTF8.GetBytes(json), context, CancellationToken.None);


    var success = Assert.IsType<BusinessStepResult<In>.Success>(result);
    Assert.Equal("ORD-1001", success.Value.OrderId);
    Assert.Single(success.Value.Lines);
}


[Fact]
public async Task ExecuteAsync_WithValidJson_StoresOrderIdAndProcessedAtInContext()
{
    var deserializer = new Deserializer();
    var context = new Context(new Dictionary<string, string>());
    var json = """{"orderId":"ORD-1001","customerId":"CUST-42","orderDate":"2026-01-15T09:30:00+00:00","lines":[]}""";


    var (_, resultContext) = await deserializer.ExecuteAsync(
        Encoding.UTF8.GetBytes(json), context, CancellationToken.None);


    Assert.Equal("ORD-1001", resultContext.Metadata[Constants.ContextKeyOrderId]);
    Assert.True(resultContext.Metadata.ContainsKey(Constants.ContextKeyProcessedAt));
}

Run the unit suite:

Terminal window
dotnet test ./test/OrderSync.Test.Unit
Passed!  - Failed:     0, Passed:     2, Skipped:     0, Total:     2 - OrderSync.Test.Unit.dll (net10.0)

Both Deserializer tests should pass.