GH2201: Add option to disable loop detection during query fetches.

Author: David Ellingsworth

src/NHibernate/Cfg/Environment.cs

@@ -110,6 +110,12 @@ public static string Version
 		public const string CurrentSessionContextClass = "current_session_context_class";
 		public const string UseSqlComments = "use_sql_comments";
 
+		/// <summary>
+		/// Enable or disable the ability to detect loops in query fetches.
+		/// The default is to detect and elimate potential fetch loops.
+		/// </summary>
+		public const string DetectFetchLoops = "detect_fetch_loops";
+
 		/// <summary> Enable formatting of SQL logged to the console</summary>
 		public const string FormatSql = "format_sql";
 

src/NHibernate/Cfg/Settings.cs

@@ -36,6 +36,7 @@ public Settings()
 		public SqlStatementLogger SqlStatementLogger { get; internal set; }
 
 		public int MaximumFetchDepth { get; internal set; }
+		public bool DetectFetchLoops { get; internal set; }
 
 		public IDictionary<string, string> QuerySubstitutions { get; internal set; }
 

src/NHibernate/Cfg/SettingsFactory.cs

@@ -92,6 +92,10 @@ public Settings BuildSettings(IDictionary<string, string> properties)
 				log.Info("Maximum outer join fetch depth: {0}", maxFetchDepth);
 			}
 
+			bool detectFetchLoops = PropertiesHelper.GetBoolean(Environment.DetectFetchLoops, properties, true);
+			log.Info("Detect fetch loops: {0}", EnabledDisabled(detectFetchLoops));
+			settings.DetectFetchLoops = detectFetchLoops;
+
 			IConnectionProvider connectionProvider = ConnectionProviderFactory.NewConnectionProvider(properties);
 			ITransactionFactory transactionFactory = CreateTransactionFactory(properties);
 			// TransactionManagerLookup transactionManagerLookup = TransactionManagerLookupFactory.GetTransactionManagerLookup( properties );

src/NHibernate/Loader/JoinWalker.cs

@@ -804,8 +804,15 @@ protected virtual string GenerateRootAlias(string description)
 		/// </summary>
 		protected virtual bool IsDuplicateAssociation(string foreignKeyTable, string[] foreignKeyColumns)
 		{
-			AssociationKey associationKey = new AssociationKey(foreignKeyColumns, foreignKeyTable);
-			return !visitedAssociationKeys.Add(associationKey);
+			bool detectFetchLoops = Factory.Settings.DetectFetchLoops;
+
+			if (detectFetchLoops)
+			{
+				AssociationKey associationKey = new AssociationKey(foreignKeyColumns, foreignKeyTable);
+				return !visitedAssociationKeys.Add(associationKey);
+			}
+
+			return false;
 		}
 
 		/// <summary>