Add post on Serilog per-sink filters

src/posts/SerilogPerSinkFilters.md

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+---
+title: Serilog Per Sink Filters
+description: A way to apply filters to only one Serilog Sink
+tags: [ Programming, C# ]
+---
+
+It's helpful to have all log events sent to the console to make development easier, but it's best to not have other logging sinks spammed with debug and verbose level logs.
+
+## Methods that don't work
+
+* The usual way to filter events in Serilog is like this:
+
+	```csharp
+	loggerConfiguration
+		.MinimumLevel.Override("Microsoft", LogEventLevel.Warning)
+		.WriteTo.Whatever()
+		.WriteTo.Console();
+	```
+
+	However, that will apply to all sinks, including the console.
+
+* Another way is to apply the override inside a sub-logger:
+
+	```csharp
+	loggerConfiguration
+		.WriteTo.Logger(loggerConfiguration2 => loggerConfiguration2
+			.MinimumLevel.Override("Microsoft", LogEventLevel.Warning)
+			.WriteTo.Whatever())
+		.WriteTo.Console();
+	```
+
+	However, the override will be ignored.
+
+* Most sinks provide a `restrictedToMinimumLevel` option, but that applies to all log event sources.
+
+## A working method
+
+A way that actually works is to use `.Filter` in a sub-logger:
+
+```csharp
+loggerConfiguration
+	.WriteTo.Logger(lc => lc
+		// These are things like "CTRL+C to exit" messages
+		// Use a sub-logger to let them go to the console, but not to the DB
+		.Filter.ByExcluding(le => Matching.FromSource("Microsoft").Invoke(le)
+			&& (le.Level == LogEventLevel.Verbose
+				|| le.Level == LogEventLevel.Debug
+				|| le.Level == LogEventLevel.Information))
+		.WriteTo.Whatever())
+	.WriteTo.Console();
+```