public class CreateOrderCommandHandler(
    IOrderRepository orderRepository,
    IProductInventoryChecker inventoryChecker,
    IUnitOfWork unitOfWork,
    IEventBus eventBus) : IRequestHandler<CreateOrderCommand, OrderDto>
{
    public async Task<OrderDto> Handle(CreateOrderCommand request, CancellationToken cancellationToken)
    {
        var order = new Order(request.CustomerId, request.ProductId, request.Quantity, inventoryChecker);

        await orderRepository.AddAsync(order);

        await unitOfWork.CommitAsync(cancellationToken);

        // 數(shù)據(jù)庫(kù)事務(wù)已完成

        await eventBus.Send(new OrderCreatedIntegrationEvent(order.Id));

        returnnew OrderDto { Id = order.Id, Total = order.Total };
    }
}

CREATE TABLE outbox_messages (
    idUUID PRIMARY KEY,
    typeVARCHAR(255) NOTNULL,
    content JSONB NOTNULL,
    occurred_on_utc TIMESTAMPWITHTIME ZONE NOTNULL,
    processed_on_utc TIMESTAMPWITHTIME ZONE NULL,
    errorTEXTNULL
);

-- 因?yàn)閷?huì)經(jīng)常查詢未處理的消息，因此可以考慮添加索引
-- 它將數(shù)據(jù)行按照我們查詢需要的正確順序排序。

CREATEINDEXIFNOTEXISTS idx_outbox_messages_unprocessed
ON outbox_messages (occurred_on_utc, processed_on_utc)
INCLUDE (id, type, content)
WHERE processed_on_utc ISNULL;

public sealed class OutboxMessage
{
    public Guid Id { get; init; }
    public string Type { get; init; }
    public string Content { get; init; }
    public DateTime OccurredOnUtc { get; init; }
    public DateTime? ProcessedOnUtc { get; init; }
    public string? Error { get; init; }
}

public async Task AddToOutbox<T>(T message, NpgsqlDataSource dataSource)
{
    var outboxMessage = new OutboxMessage
    {
        Id = Guid.NewGuid(),
        OccurredOnUtc = DateTime.UtcNow,
        Type = typeof(T).FullName, // 通過(guò)這種方式實(shí)現(xiàn)反序列化
        Content = JsonSerializer.Serialize(message)
    };

    awaitusingvar connection = await dataSource.OpenConnectionAsync();
    await connection.ExecuteAsync(
        @"""
        INSERT INTO outbox_messages (id, occurred_on_utc, type, content)
        VALUES (@Id, @OccurredOnUtc, @Type, @Content::jsonb)
        """,
        outboxMessage);
}

[DisallowConcurrentExecution]
public class OutboxProcessorJob(
    NpgsqlDataSource dataSource,
    IPublishEndpoint publishEndpoint,
    Assembly integrationEventsAssembly) : IJob
{
    public async Task Execute(IJobExecutionContext context)
    {
        awaitusingvar connection = await dataSource.OpenConnectionAsync();
        awaitusingvar transaction = await connection.BeginTransactionAsync();

        // You can make the limit a parameter, to control the batch size.
        // We can also select just the id, type, and content columns.
        var messages = await connection.QueryAsync<OutboxMessage>(
            @"""
            SELECT id AS Id, type AS Type, content AS Content
            FROM outbox_messages
            WHERE processed_on_utc IS NULL
            ORDER BY occurred_on_utc LIMIT 100
            """,
            transaction: transaction);

        foreach (var message in messages)
        {
            try
            {
                var messageType = integrationEventsAssembly.GetType(message.Type);
                var deserializedMessage = JsonSerializer.Deserialize(message.Content, messageType);

                // We should introduce retries here to improve reliability.
                await publishEndpoint.Publish(deserializedMessage);

                await connection.ExecuteAsync(
                    @"""
                    UPDATE outbox_messages
                    SET processed_on_utc = @ProcessedOnUtc
                    WHERE id = @Id
                    """,
                    new { ProcessedOnUtc = DateTime.UtcNow, message.Id },
                    transaction: transaction);
            }
            catch (Exception ex)
            {
                // We can also introduce error logging here.

                await connection.ExecuteAsync(
                    @"""
                    UPDATE outbox_messages
                    SET processed_on_utc = @ProcessedOnUtc, error = @Error
                    WHERE id = @Id
                    """,
                    new { ProcessedOnUtc = DateTime.UtcNow, Error = ex.ToString(), message.Id },
                    transaction: transaction);
            }
        }

        await transaction.CommitAsync();
    }
}