.net – 从何处运行实体的重复检查

public class JobRole
{
  public int Id { get; set; }        
  public string Name { get; set; }
}

您对ValidateEntity的问题似乎是在SaveChanges上进行验证,这对您来说太迟了.但是在Entity Framework 5.0中,如果您希望使用 DbContext.GetValidationErrors,则可以提前调用验证.当然,您也可以直接调用 DbContext.ValidateEntity.我是这样做的：

>覆盖DbContext上的ValidateEntity方法：

protected override DbEntityValidationResult 
                   ValidateEntity(DbEntityEntry entityEntry,IDictionary<object,object> items)
{
    //base validation for Data Annotations,IValidatableObject
    var result = base.ValidateEntity(entityEntry,items);

    //You can choose to bail out before custom validation
    //if (result.IsValid)
    //    return result;

    CustomValidate(result);
    return result;
}

private void CustomValidate(DbEntityValidationResult result)
{
    ValidateOrganisation(result);
    ValidateUserProfile(result);
}

private void ValidateOrganisation(DbEntityValidationResult result)
{
    var organisation = result.Entry.Entity as Organisation;
    if (organisation == null)
        return;

    if (Organisations.Any(o => o.Name == organisation.Name 
                               && o.ID != organisation.ID))
        result.ValidationErrors
              .Add(new DbValidationError("Name","Name already exists"));
}

private void ValidateUserProfile(DbEntityValidationResult result)
{
    var userProfile = result.Entry.Entity as UserProfile;
    if (userProfile == null)
        return;

    if (UserProfiles.Any(a => a.UserName == userProfile.UserName 
                              && a.ID != userProfile.ID))
        result.ValidationErrors.Add(new DbValidationError("UserName","Username already exists"));
}

>在try catch中嵌入Context.SaveChanges并创建一个访问Context.GetValidationErrors()的方法.这是在我的UnitOfWork类中：

public Dictionary<string,string> GetValidationErrors()
{
    return _context.GetValidationErrors()
                   .SelectMany(x => x.ValidationErrors)
                   .ToDictionary(x => x.PropertyName,x => x.ErrorMessage);
}

public int Save()
{
    try
    {
        return _context.SaveChanges();
    }
    catch (DbEntityValidationException e)
    {
        //http://blogs.infosupport.com/improving-dbentityvalidationexception/
        var errors = e.EntityValidationErrors
          .SelectMany(x => x.ValidationErrors)
          .Select(x => x.ErrorMessage);

        string message = String.Join("; ",errors);

        throw new DataException(message);
    }
}

>在我的控制器中,在将实体添加到上下文之后但在SaveChanges()之前调用GetValidationErrors()：

[HttpPost]
public ActionResult Create(Organisation organisation,string returnUrl = null)
{
    _uow.OrganisationRepository.InsertOrUpdate(organisation);

    foreach (var error in _uow.GetValidationErrors())
        ModelState.AddModelError(error.Key,error.Value);

    if (!ModelState.IsValid)
        return View();

    _uow.Save();

    if (string.IsNullOrEmpty(returnUrl))
        return RedirectToAction("Index");

    return Redirect(returnUrl);
}

我的基础存储库类实现了InsertOrUpdate,如下所示：

protected virtual void InsertOrUpdate(T e,int id)
    {
        if (id == default(int))
        {
            // New entity
            context.Set<T>().Add(e);
        }
        else
        {
            // Existing entity
            context.Entry(e).State = EntityState.Modified;
        }      
    }

我仍然建议为数据库添加一个唯一约束,因为这绝对可以保证您的数据完整性并提供可以提高效率的索引,但是覆盖ValidateEntry可以控制验证的发生方式和时间.