Adds events for changes cancelling

Orm/Xtensive.Orm.Tests/Storage/SessionEventsTest.cs

@@ -1,6 +1,6 @@
-// Copyright (C) 2003-2010 Xtensive LLC.
-// All rights reserved.
-// For conditions of distribution and use, see license.
+// Copyright (C) 2009-2020 Xtensive LLC.
+// This code is distributed under MIT license terms.
+// See the License.txt file in the project root for more information.
 // Created by: Alex Kofman
 // Created:    2009.10.08
 
@@ -45,6 +45,9 @@ protected override DomainConfiguration BuildConfiguration()
     private EventArgs persistingArgs;
     private EventArgs persistedArgs;
 
+    private EventArgs changesCancelingArgs;
+    private EventArgs changesCanceledArgs;
+
     private EntityEventArgs entityCreatedArgs;
     private EntityEventArgs entityRemoving;
     private EntityEventArgs entityRemoved;
@@ -100,6 +103,9 @@ public void MainTest()
         session.Events.Persisting += (sender, e) => persistingArgs = e;
         session.Events.Persisted += (sender, e) => persistedArgs = e;
 
+        session.Events.ChangesCanceling += (sender, e) => changesCancelingArgs = e;
+        session.Events.ChangesCanceled += (sender, e) => changesCanceledArgs = e;
+
         session.Events.EntityCreated += (sender, e) => entityCreatedArgs = e;
         session.Events.EntityRemoving += (sender, e) => entityRemoving = e;
         session.Events.EntityRemove += (sender, e) => entityRemoved = e;
@@ -113,6 +119,7 @@ public void MainTest()
         RollbackTransaction();
         ErrorOnCommit();
         EditEntity();
+        CancelChanges();
       }
     }
 
@@ -221,5 +228,26 @@ private void EditEntity()
         Assert.AreEqual(entity, entityRemoved.Entity);
       }
     }
+
+    private void CancelChanges()
+    {
+      var session = Session.Demand();
+      using (var transactionScope = session.OpenTransaction()) {
+        ClearEvents();
+
+        var megaEntity = new MegaEntity { Value = 1 };
+
+        session.CancelChanges();
+      }
+
+      Assert.IsNotNull(transactionRollbackingArgs);
+      Assert.IsNotNull(transactionRollbackedArgs);
+      Assert.IsNotNull(changesCancelingArgs);
+      Assert.IsNotNull(changesCanceledArgs);
+      Assert.IsNull(persistingArgs);
+      Assert.IsNull(persistedArgs);
+      Assert.IsNull(transactionCommitingArgs);
+      Assert.IsNull(transactionCommitedArgs);
+    }
   }
 }

Orm/Xtensive.Orm/Orm/Session.Persist.cs

@@ -1,6 +1,6 @@
-// Copyright (C) 2003-2010 Xtensive LLC.
-// All rights reserved.
-// For conditions of distribution and use, see license.
+// Copyright (C) 2007-2020 Xtensive LLC.
+// This code is distributed under MIT license terms.
+// See the License.txt file in the project root for more information.
 // Created by: Dmitri Maximov
 // Created:    2007.08.10
 
@@ -57,9 +57,15 @@ public void SaveChanges()
     /// <exception cref="NotSupportedException">Unable to cancel changes for non-disconnected session. Use transaction boundaries to control the state.</exception>
     public void CancelChanges()
     {
+      SystemEvents.NotifyChangesCanceling();
+      Events.NotifyChangesCanceling();
+
       CancelEntitySetsChanges();
       CancelEntitiesChanges();
       NonPairedReferencesRegistry.Clear();
+
+      SystemEvents.NotifyChangesCanceled();
+      Events.NotifyChangesCanceled();
     }
 
     internal void Persist(PersistReason reason)

Orm/Xtensive.Orm/Orm/SessionEventAccessor.cs

@@ -1,6 +1,6 @@
-// Copyright (C) 2003-2010 Xtensive LLC.
-// All rights reserved.
-// For conditions of distribution and use, see license.
+// Copyright (C) 2010-2020 Xtensive LLC.
+// This code is distributed under MIT license terms.
+// See the License.txt file in the project root for more information.
 // Created by: Alex Yakunin
 // Created:    2010.08.10
 
@@ -67,6 +67,16 @@ public sealed class SessionEventAccessor
     /// </summary>
     public event EventHandler Persisted;
 
+    /// <summary>
+    /// Occurs when <see cref="Session"/> is about to <see cref="Orm.Session.CancelChanges()"/> changes.
+    /// </summary>
+    public event EventHandler ChangesCanceling;
+
+    /// <summary>
+    /// Occurs when changes are canceled.
+    /// </summary>
+    public event EventHandler ChangesCanceled;
+
     /// <summary>
     /// Occurs when local <see cref="Key"/> created.
     /// </summary>
@@ -284,6 +294,18 @@ internal void NotifyPersisted()
         Persisted(this, EventArgs.Empty);
     }
 
+    internal void NotifyChangesCanceling()
+    {
+      if (ChangesCanceling != null && AreNotificationsEnabled())
+        ChangesCanceling(this, EventArgs.Empty);
+    }
+
+    internal void NotifyChangesCanceled()
+    {
+      if (ChangesCanceled != null && AreNotificationsEnabled())
+        ChangesCanceled(this, EventArgs.Empty);
+    }
+
     internal void NotifyKeyGenerated(Key key)
     {
       if (KeyGenerated!=null && AreNotificationsEnabled())