DbContextAbandonChanges

using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Data.Entity.Infrastructure;
using System.Linq;
using System.Web;

namespace Peder.ExtensionMethods
{
	public static class EntityFrameworkApiExtensionMethods
	{
		public static void DiscardChanges(this DbContext dbContext)
		{
			RejectScalarChanges(dbContext);
			RejectNavigationChanges(dbContext);
		}


		private static void RejectScalarChanges(DbContext dbContext)
		{
			foreach (var entry in dbContext.ChangeTracker.Entries())
			{
				switch (entry.State)
				{
					case EntityState.Modified:
					case EntityState.Deleted:
						entry.State = EntityState.Modified; //Revert changes made to deleted entity.
						entry.State = EntityState.Unchanged;
						break;
					case EntityState.Added:
						entry.State = EntityState.Detached;
						break;
				}
			}
		}

		private static void RejectNavigationChanges(DbContext dbContext)
		{
			var objectContext = ((IObjectContextAdapter)dbContext).ObjectContext;
			var deletedRelationships = objectContext.ObjectStateManager.GetObjectStateEntries(EntityState.Deleted).Where(e => e.IsRelationship && !RelationshipContainsKeyEntry(e, dbContext));
			var addedRelationships = objectContext.ObjectStateManager.GetObjectStateEntries(EntityState.Added).Where(e => e.IsRelationship);

			foreach (var relationship in addedRelationships)
				relationship.Delete();

			foreach (var relationship in deletedRelationships)
				relationship.ChangeState(EntityState.Unchanged);
		}

		private static bool RelationshipContainsKeyEntry(System.Data.Entity.Core.Objects.ObjectStateEntry stateEntry, DbContext dbContext)
		{
			//prevent exception: "Cannot change state of a relationship if one of the ends of the relationship is a KeyEntry"
			//I haven't been able to find the conditions under which this happens, but it sometimes does.
			var objectContext = ((IObjectContextAdapter)dbContext).ObjectContext;
			var keys = new[] { stateEntry.OriginalValues[0], stateEntry.OriginalValues[1] };
			return keys.Any(key => objectContext.ObjectStateManager.GetObjectStateEntry(key).Entity == null);
		}
	}
}