In the previous blog post I talked about how to change the log level at runtime by coupling the appsettings.json (or rather the IConfiguration) with the ILogger. However, the solution has one drawback: you need to change the file appsettings.json for that. In this post we will be able to change the log level without changing the configuration file.

Want to see some real code? Look at the examples on https://github.com/PawelGerr/Thinktecture.Logging.Configuration 

or just use Nuget packages: Thinktecture.Extensions.Logging.Configuration and Thinktecture.Extensions.Serilog.Configuration 

At first we need a custom implementation of IConfigurationSource and IConfigurationProvider. The actual work does the implementation of IConfigurationProvider. The IConfigurationSource is just to inject the provider into your ConfigurationBuilder.

var config = new ConfigurationBuilder()
    .Add(new LoggingConfigurationSource())
    .Build();
-----------------------------------------
public class LoggingConfigurationSource : IConfigurationSource
{
    public IConfigurationProvider Build(IConfigurationBuilder builder)
    {
        // Our implementation of IConfigurationProvider
        return new LoggingConfigurationProvider();
    }
}

As we can see, the LoggingConfigurationSource doesn't do pretty much, let us focus on LoggingConfigurationProvider or rather on the interface IConfigurationProvider.

public interface IConfigurationProvider
{
    bool TryGet(string key, out string value);
    void Set(string key, string value);
    IChangeToken GetReloadToken();
    void Load();
    IEnumerable<string> GetChildKeys(IEnumerable<string> earlierKeys, string parentPath);
}

There are 2 methods that look promising: Set(key, value) for setting a value for a specific key and GetReloadToken() to notify other components (like the logger) about changes in the configuration. Now that we know how to change the configuration values, we need to know the keys and values the logger uses to configure itself. Use Microsoft docs for a hint for Microsoft.Extensions.Logging.ILogger or Serilog.Settings.Configuration in case you are using Serilog.

The pattern for MS-logger key is <<Provider>>:LogLevel:<<Category>>. Here are some examples for the logs coming from Thinktecture components: Console:LogLevel:Thinktecture or LogLevel:Thinktecture.  The value is just one of the Microsoft.Extensions.Logging.LogLevel, like Debug.

namespace Thinktecture
{
    public class MyComponent
    {
        public MyComponent(ILogger<MyComponent> logger)
        {
            logger.LogDebug("Log from Thinktecture.Component");
        }
    }
}

Let's look at the implementation, luckily there is a base class we can use.

public class LoggingConfigurationProvider : ConfigurationProvider
{
    public void SetLevel(LogLevel level, string category = null, string provider = null)
    {
        // returns something like "Console:LogLevel:Thinktecture"
        var path = BuildLogLevelPath(category, provider);
        var levelName = GetLevelName(level); // returns log level like "Debug"

        // Data and OnReload() are provided by the base class
        Data[path] = levelName;
        OnReload(); // notifies other components
    }

    ...
}

Actually, that's it ... You can change the configuration just by setting and deleting keys in the dictionary Data and calling OnReload() afterwards. The only part that's left is to get hold of the instance of LoggingConfigurationProvider to be able to call the method SetLevel from outside but I'm pretty sure you don't need any help for that especially having access to my github repo :)

The provided solution does what we intended to, but, do we really want that simple filtering of the logs? Image you are using Entity Framework Core (EF) and there are multiple requests that modify some data. One request is able to commit the transaction the other doesn't and throws, say, an OptimisticConcurrencyException. Your code catches the exception and handles it by retrying the whole transaction, with success. Entity Framework logs this error (i.e. the SQL statement, arguments etc.) internally. The question is, should this error be logged by EF as an Error even if it has been handled by our application? If yes then our logs will be full with errors and it would seem as if we have a lot of bugs in our application. Perhaps it would be better to let EF to log its internal errors as Debug, so that this information is not lost and if our app can't handle the exception then we will log the exception as an error.

But that's for another day ...

Related Articles

.net core
.NET Core in production - Changing log level temporarily
When running the application in production then the log level is set somewhere between and . The question is what to do if you or your customer experiences some undesired behavior and the logs with present log level aren't enough to pinpoint the issue. The first solution that…
Pawel Gerr
.net
.NET Core - Lowering the log level of 3rd party components
With the new .NET Core framework and libraries we have got an interface called Microsoft.Extensions.Logging.ILogger to be used for writing log messages. Various 3rd party and built-in components make very good use of it. To see how much is being logged just create a simple Web…
Pawel Gerr
entity framework core
Do Not Waste Performance by Not Using Temp Tables With Entity Framework Core
It has been a while since I released my article about the usage of temp tables in Entity Framework (v6). Meanwhile, Microsoft has released a completely rewritten version of its O/R mapper so my old approach is no longer applicable. But before we learn about a new one, let us…
Pawel Gerr
entity framework core
Better Entity Framework Core Performance by Reading Execution Plans
Both a LINQ query and an SQL statement are descriptions that state which data should be fetched, but not how.. Sure, when reading LINQ or SQL, we can make assumptions about the performance but not in every case. Some queries are either too fancy or too big to grasp, so our…
Pawel Gerr