Question

我有一个提交数据的MVC表单。提交后，它会进入预览视图表单，用户可以决定是继续发布还是再次编辑表单。

除了提交数据外，我还提供上传图片的选项。我在此预览表单中基本上有3个场景：

更新表格并保留现有照片
更新表格并替换（或删除）现有图片
更新表格并添加图片（如果之前没有）

现在，方案2）和3）工作正常，但我正在努力的是方案1）。出于某种原因，任何现有图片（来自初始提交）都将被覆盖/删除。当我尝试调试时，我注意到我的if语句的else子句只是被跳过了。

我怀疑这与我的视图或模型有关，因此我发布了我的控制器的相关代码。

    public ActionResult UpdateErrand(
        [Bind(Exclude                       = "Picture")]errands model)
    {
        // define variables for reuse
        var userID                          = User.Identity.GetUserId();
        DateTime nowUTC                     = DateTime.Now.ToUniversalTime();
        DateTime nowLocal                   = DateTime.Now.ToLocalTime();
        // get picture and get it to bytes
        string picture                      = Request.Form["editErrandCroppedPicture"];
        byte[] imageBytes                   = Convert.FromBase64String(picture);
        // define errand
        var errand                          = new errands
        {
            // basics
            UserID                          = userID,
            FirstName                       = UserManager.FindById(userID).FirstName,
            Email                           = UserManager.FindById(userID).Email,
            Phone                           = UserManager.FindById(userID).PhoneNumber,
            //Rating                        = 

            // form
            ID                              = model.ID,
            Category                        = model.Category,
            SubCategory                     = model.SubCategory,
            Title                           = model.Title,
            Description                     = model.Description,
            Location                        = model.Location,
            ASAP                            = model.ASAP,
            StartDateTime                   = model.StartDateTime,
            DurationInHours                 = model.DurationInHours,
            EndDateTime                     = model.EndDateTime,
            DateTimePosted                  = nowLocal,
            Currency                        = model.Currency,
            Offering                        = model.Offering,
            Price                           = model.Price,
            errandTax                       = model.errandTax,
            PaymentMethod                   = model.PaymentMethod,
            LatitudePosted                  = model.LatitudePosted,
            LongitudePosted                 = model.LongitudePosted,
            LocationPosted                  = model.LocationPosted,
            Published                       = true
        };
        // workaround to ensure picture is uploaded correctly
        if (imageBytes.Length               > 2)
        {
            errand.Picture                  = imageBytes;
        }
        else
        {
            errand.Picture                  = model.Picture;
        }
        // save errand to DB
        ERRANDOM.Entry(errand).State = EntityState.Modified;
        ERRANDOM.SaveChanges();
        // track user activity: post includes activity name, timestamp along with location, and if authenticated, user ID
        var SUCCESS                         = new UserActivities
        {
            UserID                          = userID,
            ActivityName                    = "EditErrand_Success",
            ActivityTimeStampUTC            = nowUTC,
            ActivityLatitude                = model.LatitudePosted,
            ActivityLongitude               = model.LongitudePosted,
            ActivityLocation                = model.LocationPosted
        };
        ERRANDOM.UserActivityList.Add(SUCCESS);
        ERRANDOM.SaveChanges();
        return RedirectToAction("errandPreview");
    }

Answer 1

如果将实体标记为已修改（.State = EntityState.Modified），则其所有映射的标量属性（即非导航属性）都将成为SQL更新语句的一部分。但是，可以从更新中排除选定的属性。以下是如何做到这一点：

...
LatitudePosted = model.LatitudePosted,
LongitudePosted = model.LongitudePosted,
LocationPosted = model.LocationPosted,
Published = true
errand.Picture = imageBytes;

ERRANDOM.Entry(errand).State = EntityState.Modified;

if (imageBytes.Length <= 2)
{
    ERRANDOM.Entry(errand).Property(e => e.Picture).IsModified = false;
}

ERRANDOM.SaveChanges();

如您所见，您现在可以无条件地分配errand.Picture = imageBytes：稍后当它不需要更新时将被排除。在没有图片更新的情况下（这可能是）最常见的情况下，这也节省了更新差事的带宽。

Answer 2

您正在排除绑定图片，因此您的IF语句else子句将为“新”差事对象分配空值（model.Picture）。

MVC控制器if / else语句

2 个答案: