InterpolatedLogging.Microsoft.Extensions.Logging 5.0.6

Interpolated Logging

Extensions to Logging Libraries to write Log Messages using Interpolated Strings without losing Structured Property Names

Introduction

Most logging libraries support structured logging:

logger.Info("User {UserName} created Order {OrderId} at {Date}, operation took {OperationElapsedTime}ms", 
    name, orderId, DateTime.Now, elapsedTime);

This means that our logs will get not only plain strings but also the structured data, allowing us to search for specific property values (e.g. search for OrderId="123" to trace some order, or search for OperationElapsedTime>1000 to find slow operations).

The problem with this approach is that it's easy to put the wrong number of parameters or wrong order of parameters (the parameters at the end are positional, they are not matched with the message by their names).

If you just use regular interpolated strings you lose the benefit of structured logging, since the logging library won't know the names of each property:

logger.Info($"User {UserName} created Order {OrderId} at {Date}, operation took {OperationElapsedTime}ms");

This project solves this problem by extending popular logging libraries with extension methods that allow the use of interpolated strings while still being able to define the name of the properties:

// Syntax 1: Define property names using explicit NP (NamedProperty) helper
logger.InterpolatedInfo($"User {NP(name, "UserName")} created Order {NP(orderId, "OrderId")} at {NP(now, "Date")}, operation took {NP(elapsedTime, "OperationElapsedTime")}ms");

// Syntax 2: Define property names using anonymous objects
logger.InterpolatedInfo($"User {new { UserName = name }} created Order {new { OrderId = orderId}} at {new { Date = now }}, operation took {new { OperationElapsedTime = elapsedTime }}ms");

// Syntax 3: Define property names after the variables using colon-syntax ( {variable:propertyName} )
logger.InterpolatedInfo($"User {name:UserName} created Order {orderId:OrderId} at {now:Date}, operation took {elapsedTime:OperationElapsedTime}ms");

All those syntaxes above are equivalent (and have near-identical performance), so pick the one you like better.

The result is that your logging library will get this template and properties:

"User {UserName} created Order {OrderId} at {Date}, operation took {OperationElapsedTime}ms"
// ... and the properties in order: name, orderId, DateTime.Now, elapsedTime.

Why can't I just use regular string interpolation?

If you were just using regular string interpolation (without our extension methods) the final rendered log (plain message) tracked in your logging library would be the same, but the received template would be
"User {0} created Order {1} at {2}, operation took {3}ms"
and it would receive properties named like {0}="Rick", {1}=1001, etc. In this case you wouldn't be able to searches in your logging database for something like WHERE UserName=="Rick".
The best you could do would be like WHERE Template=="User {0} created Order {1} at {2}, operation took {3}ms" AND Props.{0}="Rick" - but structured logging can do much better than this.

Quickstart

1. Install the NuGet package according to your logging library (Serilog, Microsoft.Extensions.Logging or NLog)
2. Start using like this:

// for easier usage our extension methods use the same namespace of the logging libraries
// using Serilog;
// or using Microsoft.Extensions.Logging;
// or using NLog;
using static InterpolatedLogging.NamedProperties; // for using the short NP helper you need this
// ...

logger.InterpolatedInformation($"User {new { UserName = name }} created Order {new { OrderId = orderId}} at {new { Date = now }}, operation took {new { OperationElapsedTime = elapsedTime }}ms");
// there are also extensions for Debug, Verbose (or Trace depending on your logging library), etc, and there are also overloads that take an Exception.

Supported Logging Libraries

Current supported libraries:

Advanced Features

Raw strings

If you want to embed raw strings in your messages (don't want them to be saved as structured properties), you don't need to create an anonymous object and you can just use the raw modifier:

logger.InterpolatedInformation($"User {new { UserName = name }} logged as {role:raw}");

Serilog destructuring operator

Serilog has this @ destructuring operator which makes a single property be stored with its internal structure (instead of just invoking ToString() and saving the serialized property). You can still use that operator by using the @ outside of the interpolation:

var input = new { Latitude = 25, Longitude = 134 };
logger.Information($"Processed @{ new { SensorInput = input }} in { new { TimeMS = time}:000} ms.");
// in plain Serilog this would be equivalent of:
//logger.Information("Processed {@SensorInput} in {TimeMS:000}ms.", input, time);

Collaborate

This is a brand new project, and your contribution can help a lot.

Would you like to collaborate?

Please submit a pull request or if you prefer you can create an issue or contact me to discuss your idea.

License

MIT License