calling AddNlog() multi time, will add another Nlog provider

[ciiko]

on NLog.Extensions.Logging, ( 1.3.0)

• What is the current result?
  ILoggerFactory Factory = new Microsoft.Extensions.Logging.LoggerFactory();
  Factory .AddNlog();
  Factory .AddNlog();

calling AddNlog() will add another NLog provider, resulting in same line being outputted in log file

• What is the expected result?
  calling AddNlog() multi time will not add another NLog provider

• Did you checked the Internal log?
  no

• Please post full exception details (message, stacktrace, inner exceptions)
  same line being outputted in log file, in direct proportion to how many time i have call AddNlog()

• Are there any work arrounds? yes/no
  yes

• Is there a version in which it did worked?
  No

• Can you help us by writing an unit test?
  yes

[snakefoot]

Pull Requests are always welcome

[304NotModified]

Not sure if we can detect this. Someone looked at this?

[304NotModified]

We can only do this by using our own factory (planned for v2)

Currently we we call AddProvider on ILoggerFactory, and it has no hasProvider or something like that:

namespace Microsoft.Extensions.Logging
{
  /// <summary>
  /// Represents a type used to configure the logging system and create instances of <see cref="T:Microsoft.Extensions.Logging.ILogger" /> from
  /// the registered <see cref="T:Microsoft.Extensions.Logging.ILoggerProvider" />s.
  /// </summary>
  public interface ILoggerFactory : IDisposable
  {
    /// <summary>
    /// Creates a new <see cref="T:Microsoft.Extensions.Logging.ILogger" /> instance.
    /// </summary>
    /// <param name="categoryName">The category name for messages produced by the logger.</param>
    /// <returns>The <see cref="T:Microsoft.Extensions.Logging.ILogger" />.</returns>
    ILogger CreateLogger(string categoryName);

    /// <summary>
    /// Adds an <see cref="T:Microsoft.Extensions.Logging.ILoggerProvider" /> to the logging system.
    /// </summary>
    /// <param name="provider">The <see cref="T:Microsoft.Extensions.Logging.ILoggerProvider" />.</param>
    void AddProvider(ILoggerProvider provider);
  }
}

[snakefoot]

Not sure replacing the default LoggerFactory is always a good idea. See also NLog/NLog.Web#235

But it will resolve this issue. And there is already an "empty" LoggerFactory available right now.

[snakefoot]

Maybe the simple workaround is adding a new NLogProviderOptions called ClearExistingProviders. When calling AddNLog then it will remove all other providers (including previous NLog-providers), before adding itself. See also NLog/NLog.Web#192

Maybe also change NLogLoggerFactory so when calling AddNLog() using NLog-provider, then one will replace the existing NLog-provider when ClearExistingProviders=true

[304NotModified]

Maybe the simple workaround is adding a new NLogProviderOptions called ClearExistingProviders. When calling AddNLog then it will remove all other providers (including previous NLog-providers), before adding itself. See also NLog/NLog.Web#192

Sounds good to me :)

Maybe also change NLogLoggerFactory so when calling AddNLog() using NLog-provider, then one will replace the existing NLog-provider when ClearExistingProviders=true

AFAIK the NLogLoggerFactory is not used, but this is also fine to me

[snakefoot]

Since ILoggerFactory-interface is now obsolete, and AddNLog for ILoggerBuilder has been fixed in #325 to avoid double registration. Then I believe this issue has been resolved.