我有一个桌面客户端应用程序，它使用模态窗口来设置分层对象的属性。由于这是一个客户端应用程序，并且没有线程化对DbContext的访问，我在主Form上使用长时间运行的上下文传递给模态子项。
这些模态窗口使用PropertyGrid显示实体属性，还具有取消按钮。如果修改了任何数据并按下了取消按钮，则更改将反映在父表单中（我无法处理DbContext object）。
如果没有调用DbContext.SaveChanges()方法，有没有办法丢弃所做的任何更改？
更新：实体框架版本4.4。
如何在交易中包装它？
using(var scope = new TransactionScope(TransactionScopeOption.Required,
new TransactionOptions { IsolationLevel = IsolationLevel.ReadCommitted })){
// Do something
context.SaveChanges();
// Do something else
context.SaveChanges();
scope.Complete();
}
public void RejectChanges()
{
foreach (var entry in 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;
}
}
}
更新：
一些用户建议添加.ToList()以避免“收集被修改”异常。但我相信这个例外是有原因的。
你怎么得到这个例外？可能，您正在以非线程安全的方式使用上下文。
在取消对单个实体的属性所做的更改的简单情况下，您可以将当前值设置为原始值。
context.Entry(myEntity).CurrentValues.SetValues(context.Entry(myEntity).OriginalValues);
//you may also need to set back to unmodified -
//I'm unsure if EF will do this automatically
context.Entry(myEntity).State = EntityState.UnModified;
或者重新加载（但导致db命中）
context.Entry(myEntity).Reload();
这是基于Surgey Shuvalov的回答。它增加了对导航属性更改的支持。
public void RejectChanges()
{
RejectScalarChanges();
RejectNavigationChanges();
}
private void RejectScalarChanges()
{
foreach (var entry in 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 void RejectNavigationChanges()
{
var objectContext = ((IObjectContextAdapter)this).ObjectContext;
var deletedRelationships = objectContext.ObjectStateManager.GetObjectStateEntries(EntityState.Deleted).Where(e => e.IsRelationship && !this.RelationshipContainsKeyEntry(e));
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 bool RelationshipContainsKeyEntry(System.Data.Entity.Core.Objects.ObjectStateEntry stateEntry)
{
//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)this).ObjectContext;
var keys = new[] { stateEntry.OriginalValues[0], stateEntry.OriginalValues[1] };
return keys.Any(key => objectContext.ObjectStateManager.GetObjectStateEntry(key).Entity == null);
}
您可以尝试手动执行此类操作..不确定这适用于您的方案，但您可以尝试一下：
public void UndoAll(DbContext context)
{
//detect all changes (probably not required if AutoDetectChanges is set to true)
context.ChangeTracker.DetectChanges();
//get all entries that are changed
var entries = context.ChangeTracker.Entries().Where(e => e.State != EntityState.Unchanged).ToList();
//somehow try to discard changes on every entry
foreach (var dbEntityEntry in entries)
{
var entity = dbEntityEntry.Entity;
if (entity == null) continue;
if (dbEntityEntry.State == EntityState.Added)
{
//if entity is in Added state, remove it. (there will be problems with Set methods if entity is of proxy type, in that case you need entity base type
var set = context.Set(entity.GeType());
set.Remove(entity);
}
else if (dbEntityEntry.State == EntityState.Modified)
{
//entity is modified... you can set it to Unchanged or Reload it form Db??
dbEntityEntry.Reload();
}
else if (dbEntityEntry.State == EntityState.Deleted)
//entity is deleted... not sure what would be the right thing to do with it... set it to Modifed or Unchanged
dbEntityEntry.State = EntityState.Modified;
}
}
你可以申请：
context.Entry(TEntity).Reload();
我尝试它，它的工作对我来说很好。
注意：此方法（重新加载）从数据库重新加载实体，使用数据库中的值覆盖任何属性值。调用此方法后，实体将处于Unchanged状态。
我遇到了令人讨厌的惊喜 - 如果由于DbContext中的异常而需要回滚更改，则调用ChangeTracker.Entries（）会崩溃，例如
System.InvalidOperationException:
'The property 'Id' on entity type 'TestEntity' is part of a key and so cannot be modified or marked as modified.
To change the principal of an existing entity with an identifying foreign key first delete the dependent and invoke 'SaveChanges' then associate the dependent with the new principal.'
所以我想出了手动回滚的黑客版本
public async Task RollbackChanges()
{
var oldBehavoir = ChangeTracker.QueryTrackingBehavior;
var oldAutoDetect = ChangeTracker.AutoDetectChangesEnabled;
// this is the key - disable change tracking logic so EF does not check that there were exception in on of tracked entities
ChangeTracker.QueryTrackingBehavior = QueryTrackingBehavior.NoTracking;
ChangeTracker.AutoDetectChangesEnabled = false;
var entries = ChangeTracker.Entries().ToList();
foreach (var entry in entries)
{
switch (entry.State)
{
case EntityState.Modified:
await entry.ReloadAsync();
break;
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;
}
}
ChangeTracker.QueryTrackingBehavior = oldBehavoir;
ChangeTracker.AutoDetectChangesEnabled = oldAutoDetect;
}