如何避免EF中新添加记录的乐观并发错误

Question

我在MVC 5项目中使用Entity Framework 6，在Experiment和FileAttachment之间存在实体关系（一个Experiment可以提供多个FileAttachment）。 在“编辑实验”记录期间，我加载了一个包含两个实体的ViewModel并在编辑模式下列出了该实验下的附件：

该方案如下所述：

1）每个FileAttachment都有一个Delete按钮，当用户删除附件时，它会通过AJAX删除并在同一模式窗口中显示一条信息消息。

2）但是，如果用户在删除附件后添加新附件并保存实验，则会遇到以下错误：

“存储更新，插入或删除语句影响了意外的行数（0）。自加载实体以来，实体可能已被修改或删除。”

• 我认为原因是：我加载了Experiment和FileAttachment实体，然后通过删除一条记录来更改FileAttachment实体。 但是仍然有第一次加载的相同实体，我想保存过时的实体。 因此，也许我需要创建一个实体并在保存之前填充它，但是context.Entry(f).State = EntityState.Added, context.Entry(f).State = EntityState.Modified和context.Entry(f).State = EntityState.Unchanged没有任何意义。 我应该怎么做才能简单地将新添加的FileAttachment附加到数据库 ？

楷模：

public class Experiment
{
    [Key]
    public int Id { get; set; }

    public int Number { get; set; }

    public string Name { get; set; }

    //Navigation Properties 
    public virtual ICollection<FileAttachment> FileAttachments { get; set; }
}



public class FileAttachment
{
    [Key]
    public int Id { get; set; }

    public int ExperimentId { get; set; }

    public string FileName { get; set; }

    public byte[] FileData { get; set; }

    [HiddenInput(DisplayValue = false)]
    public string FileMimeType { get; set; }

    //Navigation Properties 
    public virtual Experiment Experiment { get; set; }
}

视图模型：

public class ExperimentViewModel
{
    //code omitted for brevity

    [DataType(DataType.Upload)]
    public IEnumerable<HttpPostedFileBase> FileUpload { get; set; }

    public virtual ICollection<FileAttachment> FileAttachments { get; set; }
}

控制器：

public JsonResult Update([Bind(Exclude = null)] ExperimentViewModel model)
{
    List<FileAttachment> fa = new List<FileAttachment>();
    //code omitted for brevity (At this step I add all the attachments in the model to "fa" paarmeter)

    //Mapping ViewModel to Entity Model (ExperimentViewModel > Experiment) :::::::::::::::::
    var config = new MapperConfiguration(cfg =>
    {
        cfg.CreateMap<ExperimentViewModel, Experiment>();
    });

    IMapper mapper = config.CreateMapper();
    //var source = new ExperimentViewModel();
    var dest = mapper.Map<ExperimentViewModel, Experiment>(model);
    ////::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

    repository.SaveExperimentWithAttachment(dest, fa);
}

具体：

public void SaveExperimentWithAttachment(Experiment experiment, IEnumerable<FileAttachment> fileAttachment)
{ 

    //Update Block 
    using (var context = new EFDbContext())
    {
        context.Entry(experiment).State = EntityState.Modified;
        foreach (FileAttachment f in fileAttachment)
        {
            context.Entry(f).State = EntityState.Modified;
        }
        context.SaveChanges(); 
    }
}

Answer 1

这是通过@StephenMuecke和@ haim770修复问题的最终答案。 非常感谢你们的努力和帮助。

public void SaveExperimentWithAttachment(Experiment experiment, IEnumerable<FileAttachment> fileAttachment)
{
    using (var context = new EFDbContext())
    {
        context.Entry(experiment).State = EntityState.Modified;
        foreach (FileAttachment f in fileAttachment)
        {
            // !!! I forgot to update the ExperimentId field for each file attachment
            f.ExperimentId = experiment.Id;
            context.Entry(f).State = EntityState.Added; //Because file attachment(s) is not updated, newly ADDED
        }
        context.SaveChanges();
    }
}