c# - EF ObjectStateEntry OriginalValues 包含 CurrentValues

Question

我正在尝试覆盖实体框架的SaveChanges()方法来保存审计信息。我从以下内容开始：

public override int SaveChanges()
{
    ChangeTracker.DetectChanges();
    ObjectContext ctx = ((IObjectContextAdapter)this).ObjectContext;
    List<ObjectStateEntry> objectStateEntryList = ctx.ObjectStateManager.GetObjectStateEntries(
                                                         EntityState.Added
                                                       | EntityState.Modified
                                                       | EntityState.Deleted).ToList();

    foreach (ObjectStateEntry entry in objectStateEntryList)
    {
        if (!entry.IsRelationship)
        {
            //Code that checks and records which entity (table) is being worked with
            ...

            foreach (string propertyName in entry.GetModifiedProperties())
            {
                DbDataRecord original = entry.OriginalValues;
                string oldValue = original.GetValue(original.GetOrdinal(propertyName)).ToString();

                CurrentValueRecord current = entry.CurrentValues;
                string newValue = current.GetValue(current.GetOrdinal(propertyName)).ToString();

                if (oldValue != newValue)
                {
                    AuditEntityField field = new AuditEntityField
                    {
                        FieldName = propertyName,
                        OldValue = oldValue,
                        NewValue = newValue,
                        Timestamp = auditEntity.Timestamp
                    };
                    auditEntity.AuditEntityField.Add(field);
                }
            }
        }
    }
}

我遇到的问题是我输入entry.OriginalValues和输入的entry.CurrentValues值始终是新的更新值：

Answer 1

已发现问题：

public ActionResult Edit(Branch branch)
{
    if (ModelState.IsValid)
    {
        db.Entry(branch).State = EntityState.Modified;
        db.SaveChanges();
        return RedirectToAction("Index");
    }
    return View(branch);
}

---

以上述方式保存更新似乎会导致ChangeTracker无法获取旧值。我通过简单地将 ViewModels 用于所有必需的更新来解决此问题：

public ActionResult Edit(BranchViewModel model)
{
    if (ModelState.IsValid)
    {
        Branch branch = db.Branch.Find(model.BranchId);

        if (branch.BranchName != model.BranchName)
        {
            branch.BranchName = model.BranchName;
            db.SaveChanges();
        }
        return RedirectToAction("Index");
    }
    return View(model);
}

Answer 2

对我来说最简单的方法是：

var cadastralAreaDb = await _context.CadastralAreas.FindAsync(id).ConfigureAwait(false);

  var audit = new Audit
  {
     CreatedBy = "Edi"
   };

_context.Entry(cadastralAreaDb).CurrentValues.SetValues(cadastralArea);
await _context.SaveChangesAsync(audit).ConfigureAwait(false);

这是在 ASP NET Core 3.1 中测试的

Answer 3

要从数据库中获取旧值的副本而不更新 EF 实体，您可以使用

context.Entry(yourEntity).GetDatabaseValues().ToObject()

或者

yourEntity.GetDatabaseValues().ToObject()

注意：这确实会引发数据库调用。