尝试保存更新时,由于相同的主键而附加实体时出错

Question

我正在尝试保存对现有数据库条目的更新,但是当我这样做时,我收到错误:

附加类型为"FFInfo.DAL.Location"的实体失败,因为同一类型的另一个实体已具有相同的主键值.如果图中的任何实体具有冲突的键值,则在使用"附加"方法或将实体的状态设置为"未更改"或"已修改"时,可能会发生这种情况.这可能是因为某些实体是新的并且尚未收到数据库生成的键值.在这种情况下,使用"添加"方法或"已添加"实体状态来跟踪图形,然后根据需要将非新实体的状态设置为"未更改"或"已修改".

这是我的控制器代码.我正在使用的保存方法与我在其他几个方面使用的保存方法相同,可以毫无问题地更新数据.

[HttpPost, ValidateAntiForgeryToken]
public ActionResult EditLocation(AddEditLocationVM model, HttpPostedFileBase MapFile)
{
    try
    {
        using (var db = new GeographyContext())
        {
            model.Sections = new SelectList(db.Sections.Where(s => s.ID > 1).OrderBy(s => s.Title), "ID", "Title").ToList();
            model.GeographyTypes = new SelectList(db.GeographyTypes.Where(gt => gt.SectionID == model.Section).OrderBy(gt => gt.Name), "ID", "Name").ToList();
            model.ParentLocations = new SelectList(db.Locations.Where(l => l.SectionID == model.Section).OrderBy(l => l.Name), "ID", "Name").ToList();


            if (MapFile != null)
            {
                if (FileHelper.IsNotValidImage(MapFile))
                {
                    ModelState.AddModelError("Invaalid File Type", "Images must be JPG, GIF, or PNG files.");
                }
            }

            if (ModelState.IsValid)
            {
                if (MapFile != null)
                {
                    var SectionRoute = db.Sections.Where(s => s.ID == model.Section).Select(s => s.Route).First();
                    model.MapFileID = FileHelper.UploadFile("Images/" + SectionRoute + "/Maps/" + MapFile.FileName.ToList(), "site", MapFile);
                }

                if (model.ParentLocation == 0)
                {
                    model.ParentLocation = null;
                }

                var UpdatedLocation = new Location()
                {
                    Description = model.Description,
                    GeographyTypeID = model.GeographyType,
                    ID = model.ID,
                    MapFileID = model.MapFileID,
                    Name = model.Name,
                    ParentLocationID = model.ParentLocation,
                    SectionID = model.Section
                };

                db.Entry(UpdatedLocation).State = EntityState.Modified;
                db.SaveChanges();
                ViewBag.Results = "Location information updated.";
            }

            return View(model);
        }
    }
    catch (Exception ex)
    {
        ErrorSignal.FromCurrentContext().Raise(ex);
        model.Sections = Enumerable.Empty<SelectListItem>();
        ViewBag.Results = "Error updating location informaiton, please try again later.";
        return View(model);
    }
}

这是我的位置实体代码:

public class Location
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int ID { get; set; }

    [Required, Index("IX_Location", 1, IsUnique = true)]
    public string Name { get; set; }

    [Index("IX_Location", 2, IsUnique = true)]
    public Int16 SectionID { get; set; }

    [Column(TypeName = "varchar(MAX)")]
    public string Description { get; set; }

    public Int16 GeographyTypeID { get; set; }
    public int? MapFileID { get; set; }
    public int? ParentLocationID { get; set; }

    [ForeignKey("SectionID")]
    public Section Section { get; set; }

    [ForeignKey("GeographyTypeID")]
    public GeographyType GeographyType { get; set; }

    [ForeignKey("MapFileID")]
    public File Map { get; set; }

    [ForeignKey("ParentLocationID")]
    public Location ParentLocation { get; set; }

    public ICollection<LocationTransitionPoint> TransitionPoints { get; set; }
}

这是我第一次尝试更新这样一个更复杂的实体,但是从我在网上找到的内容我看不出有什么不对.

Answer 1

实体框架中的内存中不能有两个具有相同主键的实体(相同类型).

问题是

model.ParentLocations = new SelectList(db.Locations.Where(l => l.SectionID == model.Section).OrderBy(l => l.Name), "ID", "Name").ToList();

在上面的行你以某种方式加载了Location它ID是什么model.ID

然后在

var UpdatedLocation = new Location()
{
    Description = model.Description,
    GeographyTypeID = model.GeographyType,
    ID = model.ID,
    MapFileID = model.MapFileID,
    Name = model.Name,
    ParentLocationID = model.ParentLocation,
    SectionID = model.Section
};
db.Entry(UpdatedLocation).State = EntityState.Modified;

您正在创建一个新的Location并尝试将其附加到上下文(通过将其状态设置为已修改),但您已将另一个Location具有确切主键的实体加载UpdatedLocation到内存中,这会导致异常.

尝试获取位置,然后更改属性.

var UpdateLocation = db.Locations.First(l => l.ID == model.ID);
// var UpdateLocation = db.Locations.Find(model.ID); maybe a better option
UpdatedLocation.Description = model.Description;
UpdatedLocation.GeographyTypeID = model.GeographyType;
UpdatedLocation.MapFileID = model.MapFileID;
UpdatedLocation.Name = model.Name;
UpdatedLocation.ParentLocationID = model.ParentLocation;
UpdatedLocation.SectionID = model.Section;