DiagnosticObserver does not use null connection (#845)

* DiagnosticObserver does not use null connection

* Make TryGetSqlConnection static.

Co-authored-by: Dave Smith <dave.smith@ventivtech.com>

src/DotNetCore.CAP.SqlServer/Diagnostics/DiagnosticObserver.cs

@@ -13,9 +13,7 @@ namespace DotNetCore.CAP.SqlServer.Diagnostics
 {
     internal class DiagnosticObserver : IObserver<KeyValuePair<string, object>>
     {
-        public const string SqlAfterCommitTransaction = "System.Data.SqlClient.WriteTransactionCommitAfter";
         public const string SqlAfterCommitTransactionMicrosoft = "Microsoft.Data.SqlClient.WriteTransactionCommitAfter";
-        public const string SqlErrorCommitTransaction = "System.Data.SqlClient.WriteTransactionCommitError";
         public const string SqlErrorCommitTransactionMicrosoft = "Microsoft.Data.SqlClient.WriteTransactionCommitError";
 
         private readonly ConcurrentDictionary<Guid, List<MediumMessage>> _bufferList;
@@ -38,9 +36,9 @@ namespace DotNetCore.CAP.SqlServer.Diagnostics
 
         public void OnNext(KeyValuePair<string, object> evt)
         {
-            if (evt.Key == SqlAfterCommitTransaction || evt.Key == SqlAfterCommitTransactionMicrosoft)
+            if (evt.Key == SqlAfterCommitTransactionMicrosoft)
             {
-                var sqlConnection = (SqlConnection)GetProperty(evt.Value, "Connection");
+                if (!TryGetSqlConnection(evt, out SqlConnection sqlConnection)) return;
                 var transactionKey = sqlConnection.ClientConnectionId;
                 if (_bufferList.TryRemove(transactionKey, out var msgList))
                     foreach (var message in msgList)
@@ -48,15 +46,21 @@ namespace DotNetCore.CAP.SqlServer.Diagnostics
                         _dispatcher.EnqueueToPublish(message);
                     }
             }
-            else if (evt.Key == SqlErrorCommitTransaction || evt.Key == SqlErrorCommitTransactionMicrosoft)
+            else if (evt.Key == SqlErrorCommitTransactionMicrosoft)
             {
-                var sqlConnection = (SqlConnection)GetProperty(evt.Value, "Connection");
+                if (!TryGetSqlConnection(evt, out SqlConnection sqlConnection)) return;
                 var transactionKey = sqlConnection.ClientConnectionId;
 
                 _bufferList.TryRemove(transactionKey, out _);
             }
         }
 
+        private static bool TryGetSqlConnection(KeyValuePair<string, object> evt, out SqlConnection sqlConnection)
+        {
+            sqlConnection = GetProperty(evt.Value, "Connection") as SqlConnection;
+            return sqlConnection != null;
+        }
+
         private static object GetProperty(object _this, string propertyName)
         {
             return _this.GetType().GetTypeInfo().GetDeclaredProperty(propertyName)?.GetValue(_this);