Structured Logging

What is Structured Logging?

Structured logging stores log data as structured data (key-value pairs) instead of plain text, making logs easier to search and analyze.

String Interpolation vs Message Templates

❌ Bad: String Interpolation

_logger.LogInformation($"Product {productId} created by {userId}");

Output: "Product 123 created by user456" (plain text)

✅ Good: Message Templates

_logger.LogInformation("Product {ProductId} created by {UserId}", productId, userId);

Output: Structured data with properties ProductId=123, UserId="user456"

Named Parameters

Use PascalCase names in curly braces for parameters.

_logger.LogInformation(
    "Order {OrderId} placed by {CustomerName} for {TotalAmount:C}",
    orderId,
    customerName,
    totalAmount
);

Format Specifiers

// Currency
_logger.LogInformation("Price: {Price:C}", 19.99); // $19.99

// Decimal places
_logger.LogInformation("Percentage: {Percent:P2}", 0.1234); // 12.34%

// Date
_logger.LogInformation("Date: {Date:yyyy-MM-dd}", DateTime.Now);

Benefits of Structured Logging

• Searchable: Query by specific properties
• Analyzable: Aggregate and analyze data
• Filterable: Filter by property values
• Machine-readable: Easy to parse programmatically

InvenTrack Example

public async Task<IActionResult> CreateOrder(Order order)
{
    _logger.LogInformation(
        "Creating order for customer {CustomerId} with {ItemCount} items, total {TotalAmount:C}",
        order.CustomerId,
        order.Items.Count,
        order.TotalAmount
    );

    try
    {
        await _context.Orders.AddAsync(order);
        await _context.SaveChangesAsync();

        _logger.LogInformation(
            "Order {OrderId} created successfully",
            order.Id
        );

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

Key Takeaways

• Structured logging: Key-value pairs, not plain text
• Message templates: Use {PropertyName} placeholders
• Don't use string interpolation: Use parameters instead
• PascalCase: Name parameters in PascalCase
• Format specifiers: {Price:C}, {Percent:P2}, etc.
• Benefits: Searchable, analyzable, filterable