From 3f07a9cfaf0ca0a15b24a079227c0ab0fb68a71e Mon Sep 17 00:00:00 2001
From: Rolf Kristensen <snakefoot@users.noreply.github.com>
Date: Tue, 21 Jan 2020 22:20:00 +0100
Subject: [PATCH] NLogLoggerFactory - Emulate Microsoft LoggerFactory by
 returning same ILogger instance (#380)

---
 .../Logging/NLogLogger.cs                       |  6 ++++++
 .../Logging/NLogLoggerFactory.cs                | 13 ++++++++++++-
 .../Logging/NLogLoggerFactoryTests.cs           | 17 +++++++++++++++++
 3 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/src/NLog.Extensions.Logging/Logging/NLogLogger.cs b/src/NLog.Extensions.Logging/Logging/NLogLogger.cs
index 252fbc8e..3b726e04 100644
--- a/src/NLog.Extensions.Logging/Logging/NLogLogger.cs
+++ b/src/NLog.Extensions.Logging/Logging/NLogLogger.cs
@@ -402,6 +402,12 @@ private bool IsEnabled(LogLevel logLevel)
             return _logger.IsEnabled(logLevel);
         }
 
+        /// <inheritdoc />
+        public override string ToString()
+        {
+            return LoggerName;
+        }
+
         /// <summary>
         /// Convert log level to NLog variant.
         /// </summary>
diff --git a/src/NLog.Extensions.Logging/Logging/NLogLoggerFactory.cs b/src/NLog.Extensions.Logging/Logging/NLogLoggerFactory.cs
index 0a671568..dd529ed8 100644
--- a/src/NLog.Extensions.Logging/Logging/NLogLoggerFactory.cs
+++ b/src/NLog.Extensions.Logging/Logging/NLogLoggerFactory.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using Microsoft.Extensions.Logging;
 using NLog.Common;
 
@@ -9,6 +10,8 @@ namespace NLog.Extensions.Logging
     /// </summary>
     public class NLogLoggerFactory : ILoggerFactory
     {
+        private readonly Dictionary<string, Microsoft.Extensions.Logging.ILogger> _loggers = new Dictionary<string, Microsoft.Extensions.Logging.ILogger>(StringComparer.Ordinal);
+
         private readonly NLogLoggerProvider _provider;
 
         /// <summary>
@@ -66,7 +69,15 @@ protected virtual void Dispose(bool disposing)
         /// <returns>The <see cref="T:Microsoft.Extensions.Logging.ILogger" />.</returns>
         public Microsoft.Extensions.Logging.ILogger CreateLogger(string categoryName)
         {
-            return _provider.CreateLogger(categoryName);
+            lock (_loggers)
+            {
+                if (!_loggers.TryGetValue(categoryName, out var logger))
+                {
+                    logger = _provider.CreateLogger(categoryName);
+                    _loggers[categoryName] = logger;
+                }
+                return logger;
+            }
         }
 
         /// <summary>
diff --git a/test/NLog.Extensions.Logging.Tests/Logging/NLogLoggerFactoryTests.cs b/test/NLog.Extensions.Logging.Tests/Logging/NLogLoggerFactoryTests.cs
index ce9e314b..f04551ce 100644
--- a/test/NLog.Extensions.Logging.Tests/Logging/NLogLoggerFactoryTests.cs
+++ b/test/NLog.Extensions.Logging.Tests/Logging/NLogLoggerFactoryTests.cs
@@ -56,5 +56,22 @@ public void AddProvider_StateUnderTest_ExpectedBehavior()
             // Assert
             Assert.Single(logFactory.Configuration.FindTargetByName<Targets.MemoryTarget>("output").Logs);
         }
+
+        [Fact]
+        public void CreateLogger_SameName_ReturnsSameInstanceTest()
+        {
+            // Arrange
+            var loggerFactory = new NLogLoggerFactory();
+            string loggerName = "namespace.class1";
+
+            // Act
+            var result1 = loggerFactory.CreateLogger(loggerName);
+            var result2 = loggerFactory.CreateLogger(loggerName);
+
+            // Assert
+            Assert.NotNull(result1);
+            Assert.Equal(loggerName, result1.ToString());
+            Assert.Same(result1, result2);
+        }
     }
 }