Fix DatabaseDeveloperPageExceptionFilter to handle wrapped DbExceptions

Sometimes EF (or other libraries) wrap database errors. The exception filter should account for this, but was not doing. This was revealed by dotnet/efcore#25050 where we started treating more error numbers as transient and hence wrapping their exceptions.

Note that the original Diagnostics.EFCore.FunctionalTests have a test for this, but it appears that these tests were never updated when the mechanism was changed in .NET 5.

src/Middleware/Diagnostics.EntityFrameworkCore/src/DatabaseDeveloperPageExceptionFilter.cs

@@ -45,7 +45,10 @@ public DatabaseDeveloperPageExceptionFilter(ILogger<DatabaseDeveloperPageExcepti
         /// <inheritdoc />
         public async Task HandleExceptionAsync(ErrorContext errorContext, Func<ErrorContext, Task> next)
         {
-            if (!(errorContext.Exception is DbException))
+            var dbException = errorContext.Exception as DbException
+                  ?? errorContext.Exception?.InnerException as DbException;
+
+            if (dbException == null)
             {
                 await next(errorContext);
                 return;
@@ -76,7 +79,7 @@ public async Task HandleExceptionAsync(ErrorContext errorContext, Func<ErrorCont
                     {
                         var page = new DatabaseErrorPage
                         {
-                            Model = new DatabaseErrorPageModel(errorContext.Exception, contextDetails, _options, errorContext.HttpContext.Request.PathBase)
+                            Model = new DatabaseErrorPageModel(dbException, contextDetails, _options, errorContext.HttpContext.Request.PathBase)
                         };
 
                         await page.ExecuteAsync(errorContext.HttpContext);

src/Middleware/Diagnostics.EntityFrameworkCore/test/UnitTests/DatabaseDeveloperPageExceptionFilterTests.cs

@@ -42,6 +42,33 @@ await filter.HandleExceptionAsync(
             Assert.True(nextFilterInvoked);
         }
 
+        [Fact]
+        public async Task Wrapped_DbExceptions_HandlingFails_InvokesNextFilter()
+        {
+            var sink = new TestSink();
+            var filter = new DatabaseDeveloperPageExceptionFilter(
+                new TestLogger<DatabaseDeveloperPageExceptionFilter>(new TestLoggerFactory(sink, true)),
+                Options.Create(new DatabaseErrorPageOptions()));
+            var context = new DefaultHttpContext();
+            var exception = new InvalidOperationException("Bang!", new Mock<DbException>().Object);
+            var nextFilterInvoked = false;
+
+            await filter.HandleExceptionAsync(
+                new ErrorContext(context, exception),
+                context =>
+                {
+                    nextFilterInvoked = true;
+                    return Task.CompletedTask;
+                });
+
+            Assert.True(nextFilterInvoked);
+            Assert.Equal(1, sink.Writes.Count);
+            var message = sink.Writes.Single();
+            Assert.Equal(LogLevel.Error, message.LogLevel);
+            Assert.Contains("An exception occurred while calculating the database error page content.", message.Message);
+        }
+
+
         [Fact]
         public async Task DbExceptions_HandlingFails_InvokesNextFilter()
         {