Options and Logging

Typed settings

The options pattern binds a configuration section to a class, so you read options.PageSize instead of string keys. ILogger<T> is injected like any other service and writes structured messages.

Bind and use

Use message templates with named placeholders rather than string interpolation, so log systems can filter by property.

builder.Services.Configure<ShopOptions>(builder.Configuration.GetSection("Shop"));

app.MapGet("/size", (IOptions<ShopOptions> opt, ILogger<Program> log) =>
{
    log.LogInformation("Page size is {PageSize}", opt.Value.PageSize);
    return opt.Value.PageSize;
});

public class ShopOptions { public int PageSize { get; set; } = 20; }

Do not log secrets

Never log passwords, tokens or full request bodies. Set minimum levels per category in appsettings.json so production does not drown in Debug messages.

Quick check: Why prefer `{PageSize}` placeholders over `$"{pageSize}"` in log calls?

• They compile faster
• They are required by C#
• Values are kept as searchable properties
• They hide values from logs