Change condition to be targeted to when using old npgsql

Author: eerhardt

src/Components/Aspire.Npgsql.EntityFrameworkCore.PostgreSQL/Aspire.Npgsql.EntityFrameworkCore.PostgreSQL.csproj

@@ -26,6 +26,12 @@
     <PackageReference Include="OpenTelemetry.Extensions.Hosting" />
   </ItemGroup>
 
+  <!-- When targeting net8.0 or net9.0, we use older Npgsql versions (8.x/9.x) whose metrics
+       don't align with the OpenTelemetry spec. LEGACY_NPGSQL enables custom histogram views. -->
+  <PropertyGroup Condition="'$(TargetFramework)' == 'net8.0' or '$(TargetFramework)' == 'net9.0'">
+    <DefineConstants>$(DefineConstants);LEGACY_NPGSQL</DefineConstants>
+  </PropertyGroup>
+
   <!-- Npgsql EF needs to match the same major version as the underlying Npgsql assemblies. -->
   <!-- This is to override CentralPackageTransitivePinningEnabled -->
   <ItemGroup Condition="'$(TargetFramework)' == 'net8.0'">

src/Components/Aspire.Npgsql/NpgsqlCommon.cs

@@ -11,9 +11,10 @@ public static void AddNpgsqlMetrics(MeterProviderBuilder meterProviderBuilder)
         meterProviderBuilder
             .AddMeter("Npgsql");
 
-#if !NET10_0_OR_GREATER
-        // starting with Npgsql 10.0, the metrics align with OpenTelemetry's spec
-        // see https://github.com/npgsql/npgsql/commit/a27566ff3e75ab1f75feb6d24cb69cdbd3340ab4
+#if LEGACY_NPGSQL
+        // Npgsql versions prior to 10.0 don't align their metrics with the OpenTelemetry spec,
+        // so custom histogram bucket boundaries are needed for the duration metrics.
+        // See https://github.com/npgsql/npgsql/commit/a27566ff3e75ab1f75feb6d24cb69cdbd3340ab4
         double[] secondsBuckets = [0, 0.005, 0.01, 0.025, 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1, 2.5, 5, 7.5, 10];
 
         meterProviderBuilder