Dotnet Source Gen Logging

Convert existing logging calls to use the LoggerMessage source generator for AOT-compatible logging with no boxing overhead and compile-time template parsing.

When to Use

• Optimizing logging performance in hot paths
• Preparing for Native AOT deployment
• Organizing scattered log messages into logical groupings
• Standardizing EventIds across the codebase

Steps

1. Find ILogger usages and logging calls

   • Search for ILogger field/parameter declarations
   • Find all logging calls: LogInformation, LogWarning, LogError, LogDebug, LogTrace, LogCritical
   • Note the log message templates and parameters

2. Organize into logical groupings by domain

   • Group related log messages by their functional area, eg:
     • LoggingValidationExtensions - validation-related logs
     • LoggingAuthenticationExtensions - auth-related logs
     • LoggingDatabaseExtensions - database-related logs
     • LoggingHttpExtensions - HTTP-related logs
     • LoggingCacheExtensions - caching-related logs
     • LoggingMessagingExtensions - messaging/queue-related logs

3. Create partial static classes with extension methods

   public static partial class LoggingValidationExtensions
   {
       [LoggerMessage(
           EventId = 1001,
           Level = LogLevel.Warning,
           Message = "Validation failed for {EntityType}: {Errors}")]
       public static partial void ValidationFailed(
           this ILogger logger, string entityType, string errors);
   }
   

4. Use EventId ranges per category

   • 1000-1999: Validation
   • 2000-2999: Authentication
   • 3000-3999: Database
   • 4000-4999: HTTP
   • 5000-5999: Cache
   • 6000-6999: Messaging
   • 7000-7999: General/Application

5. Replace inline logging calls with extension method calls

   • Before: _logger.LogWarning("Validation failed for {entityType}: {errors}", type, errs)
   • After: _logger.ValidationFailed(type, errs)

6. Verify with build

   dotnet build
   

7. If build fails, review errors:

   • Missing using statements for the extension class namespace
   • Parameter type mismatches
   • Duplicate EventIds

8. Report results:

   • List all created extension classes
   • Show count of converted log messages per category
   • Confirm build status

Key Notes

• Requires .NET 6+ - the source generator is built into the SDK
• Avoids boxing - value types are not boxed when passed to the generated methods
• Template parsed once - message template is parsed at compile time, not runtime
• Use PascalCase for placeholders - {EntityType} not {entityType} (matching is case-insensitive, but PascalCase is the recommended convention)
• Extension methods - allows fluent logger.MethodName() syntax
• Partial classes - required for source generator to emit the implementation

Example Conversion

Before:

_logger.LogInformation("User {UserId} logged in from {IpAddress}", userId, ip);
_logger.LogWarning("Failed login attempt for {Username}", username);

After:

// In LoggingAuthenticationExtensions.cs
public static partial class LoggingAuthenticationExtensions
{
    [LoggerMessage(
        EventId = 2001,
        Level = LogLevel.Information,
        Message = "User {UserId} logged in from {IpAddress}")]
    public static partial void UserLoggedIn(
        this ILogger logger, string userId, string ipAddress);

    [LoggerMessage(
        EventId = 2002,
        Level = LogLevel.Warning,
        Message = "Failed login attempt for {Username}")]
    public static partial void FailedLoginAttempt(
        this ILogger logger, string username);
}

// Usage
_logger.UserLoggedIn(userId, ip);
_logger.FailedLoginAttempt(username);