如何获取实体的旧值？

Question

如何获取实体的旧值？

按照这个例子..

public void Update(User user)
    ValidateEntity(user, OperationType.Update);

    oldUser = (how do I get the old values ​​(database) of the entity User?)

    Set.Attach(user);
    Context.ObjectStateManager.ChangeObjectState(user, EntityState.Modified);
    Context.SaveChanges();

    OnUpdated(user, oldUser);
}

Answer 1

试试这个：

public void Update(User user)
    ValidateEntity(user, OperationType.Update);

    var oldUser = Set.Single(u => u.Id == user.Id);
    Context.Detach(oldUser);

    Set.Attach(user);
    Context.ObjectStateManager.ChangeObjectState(user, EntityState.Modified);
    Context.SaveChanges();

    OnUpdated(user, oldUser);
}

或者这个：

public void Update(User user) 
{
    ValidateEntity(user, OperationType.Update);

    var oldUser = Set.Single(u => u.Id == user.Id);
    Set.ApplyCurrentValues(user);
    Context.SaveChanges(SaveOptions.DetectChangesBeforeSave);

    OnUpdated(user, Context.ObjectStateManager.GetOjectStateEntry(user).OriginalValues);

    Context.AcceptAllChanges(); 
}

Answer 2

我找到了一种使用反射将 DbDataRecord 转换为实体类型的方法...

其中 http ://www.instanceofanobject.com/2011/01/ef4-dbdatarecord-convertto.html

    public static class AnonymousTypeConversion
    {
        /// 
        /// Converts a single DbDataRwcord object into something else.
        /// The destination type must have a default constructor.
        /// 
        /// 
        /// 
        /// 
        public static T ConvertTo(this DbDataRecord record)
        {
            T item = Activator.CreateInstance();
            for (int f = 0; f 
        /// Converts a list of DbDataRecord to a list of something else.
        /// 
        /// 
        /// 
        /// 
        public static List ConvertTo(this List list)
        {
            List result = (List)Activator.CreateInstance>();

            list.ForEach(rec =>
            {
                result.Add(rec.ConvertTo());
            });

            return result;
        }
    }