Interview Question

How can you enable logging of SQL queries generated by Entity Framework Core?

Answer

There are several ways to enable SQL query logging in EF Core:

1. Using LogTo Method

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
    optionsBuilder
        .LogTo(Console.WriteLine) // Log to console
        .EnableSensitiveDataLogging() // Optional: Include parameter values
        .EnableDetailedErrors(); // Optional: More detailed error messages
}

2. Using Microsoft.Extensions.Logging

// In Program.cs or Startup.cs
builder.Services.AddDbContext<ApplicationDbContext>(options =>
    options.UseSqlServer(connectionString)
           .UseLoggerFactory(LoggerFactory.Create(builder =>
           {
               builder
                   .AddConsole()
                   .AddFilter((category, level) => 
                       category == DbLoggerCategory.Database.Command.Name && 
                       level == LogLevel.Information);
           })));

3. Using ILoggerFactory in DbContext

public class ApplicationDbContext : DbContext
{
    public static readonly ILoggerFactory MyLoggerFactory
        = LoggerFactory.Create(builder =>
        {
            builder
                .AddFilter((category, level) =>
                    category == DbLoggerCategory.Database.Command.Name &&
                    level == LogLevel.Information)
                .AddConsole();
        });

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseLoggerFactory(MyLoggerFactory);
    }
}

Key Points 💡

• LogTo is simplest for quick debugging
• ILoggerFactory is better for production use
• EnableSensitiveDataLogging shows parameter values
• Consider logging performance impact in production

Common Follow-up Questions

1. How do you log queries to a file instead of console?
2. How can you filter specific types of database operations?
3. What’s the performance impact of query logging?