Logging

Short Introduction

Logging in .NET Core provides a built-in, extensible logging framework that supports multiple logging providers and structured logging.

Official Definition

The .NET logging system provides a logging API that works with a variety of built-in and third-party logging providers, enabling developers to log messages with different severity levels.

Usage

// Program.cs - Configure logging
builder.Logging.ClearProviders();
builder.Logging.AddConsole();
builder.Logging.AddDebug();
builder.Logging.AddEventSourceLogger();

// Add Serilog (popular third-party logger)
builder.Host.UseSerilog((context, configuration) =>
    configuration.ReadFrom.Configuration(context.Configuration));

Log Levels

• Trace: Very detailed logs
• Debug: Debug information
• Information: General information
• Warning: Warning messages
• Error: Error messages
• Critical: Critical errors

Use Cases

• Application monitoring
• Debugging and troubleshooting
• Audit trails
• Performance monitoring
• Security monitoring

Sample Usage

public class OrderService : IOrderService
{
    private readonly ILogger<OrderService> _logger;
    private readonly IOrderRepository _orderRepository;

    public OrderService(ILogger<OrderService> logger, IOrderRepository orderRepository)
    {
        _logger = logger;
        _orderRepository = orderRepository;
    }

    public async Task<Order> CreateOrderAsync(CreateOrderDto dto)
    {
        _logger.LogInformation("Creating order for customer {CustomerId}", dto.CustomerId);

        try
        {
            var order = new Order
            {
                CustomerId = dto.CustomerId,
                OrderDate = DateTime.UtcNow,
                Items = dto.Items.Select(i => new OrderItem
                {
                    ProductId = i.ProductId,
                    Quantity = i.Quantity
                }).ToList()
            };

            var createdOrder = await _orderRepository.CreateAsync(order);

            _logger.LogInformation("Order {OrderId} created successfully for customer {CustomerId}",
                createdOrder.Id, dto.CustomerId);

            return createdOrder;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Failed to create order for customer {CustomerId}", dto.CustomerId);
            throw;
        }
    }
}

// Structured logging with Serilog
Log.Information("User {UserId} placed order {OrderId} for {Amount:C}",
    userId, orderId, totalAmount);