无法跟踪实体类型“x”的实例，因为已经在跟踪具有相同键值 {'a', 'b'} 的另一个实例

Question

我在编辑多对多关系之间的关系表时出现标题错误。它不会让表上出现重复，所以我尝试删除行然后创建新行，但它不起作用。

public void Update(ThermoformProduct entity, int[] thermoformCategoryIds)
{
    using (var context = new ShopContext())
    {
        var product = context.ThermoformProducts                  
            .Include(i => i.ThermoformProductCategories)                
            .FirstOrDefault(i => i.ProductId == entity.ProductId);            

        if (product != null)
        {           
            product.Code = entity.Code;
            product.Culture = entity.Culture;
            product.Renk = entity.Renk;
            product.UstGenislik = entity.UstGenislik;
            product.UstCap = entity.UstCap;
            product.AltCap = entity.AltCap;
            product.TbCap = entity.TbCap;
            product.Yukseklik = entity.Yukseklik;
            product.Hacim = entity.Hacim;
            product.TamHacim = entity.TamHacim;
            product.Baski = entity.Baski;
            product.SosisIciAdet = entity.SosisIciAdet;
            product.KoliIciAdet = entity.KoliIciAdet;
            product.ImageUrl = entity.ImageUrl;

            product.ThermoformProductCategories.RemoveAll(s=>s.ProductId == product.ProductId);

            product.ThermoformProductCategories = thermoformCategoryIds.Select(catid =>  new ThermoformProductCategory()
            {
                ProductId = product.ProductId,
                ThermoformProduct = product,
                CategoryId = catid,
                ThermoformCategory = context.ThermoformCategories.Where(i => i.CategoryId == catid).FirstOrDefault()

            }).ToList();

            context.SaveChanges();
        }
    }
}

Answer 1

EF 无法跟踪具有相同主键的实体类型的两个不同实例。您已包含相关的 ThermoformProductCategory 实体，因此它们正在被上下文跟踪。当您删除它们时，它们会从该产品的 ThermoformProductCategories 属性中清除，但它们不会从上下文中删除，并且仍在被跟踪。最后，当您创建 ThermoformProductCategory 的新列表时，一些新的主键与以前的主键匹配（已经存在于上下文中）

由于您要再次创建整个列表，因此您不需要首先获取相关实体。只需分配一个新列表，EF 就会替换整个相关实体列表 -

var product = context.ThermoformProducts.FirstOrDefault(i => i.ProductId == entity.ProductId);
if (product != null)
{       
    // set all the properties

    product.ThermoformProductCategories = thermoformCategoryIds.Select(catid =>  new ThermoformProductCategory()
    {
        ProductId = product.ProductId,
        CategoryId = catid
    }).ToList();

    context.SaveChanges();     
}

Answer 2

两件事：

1. 过滤器是多余的 - ThermoformProductCategories 导航属性应该已经被过滤了。

product.ThermoformProductCategories.RemoveAll(s=>s.ProductId == product.ProductId);

改为这样做：

product.ThermoformProductCategories.RemoveAll(); // Or .Clear()

1. 在这种情况下不要设置导航属性，只设置外键值 - 这应该可以解决您的问题：

代替：

product.ThermoformProductCategories = thermoformCategoryIds.Select(catid =>  new ThermoformProductCategory()
{
    ProductId = product.ProductId,
    ThermoformProduct = product,
    CategoryId = catid,
    ThermoformCategory = context.ThermoformCategories.Where(i => i.CategoryId == catid).FirstOrDefault()

}).ToList();

做：

product.ThermoformProductCategories = thermoformCategoryIds.Select(catid =>  new ThermoformProductCategory()
{
    ProductId = product.ProductId, // Even this might be redundant since you're adding to the product navigation property list.
    CategoryId = catid
}).ToList();

Answer 3

两个答案都是解决方案，如果有人遇到麻烦，这是我的最终形式

 public void Update(ThermoformProduct entity, int[] thermoformCategoryIds)
    {
        using (var context = new ShopContext())
        {
            var product = context.ThermoformProducts                  
                .FirstOrDefault(i => i.ProductId == entity.ProductId);            

            if (product != null)
            {
                
                product.Code = entity.Code;
                product.Culture = entity.Culture;
                product.Renk = entity.Renk;
                product.UstGenislik = entity.UstGenislik;
                product.UstCap = entity.UstCap;
                product.AltCap = entity.AltCap;
                product.TbCap = entity.TbCap;
                product.Yukseklik = entity.Yukseklik;
                product.Hacim = entity.Hacim;
                product.TamHacim = entity.TamHacim;
                product.Baski = entity.Baski;
                product.SosisIciAdet = entity.SosisIciAdet;
                product.KoliIciAdet = entity.KoliIciAdet;
                product.ImageUrl = entity.ImageUrl;
             
                var cmd = "delete from ThermoformProductCategory where ProductId=@p0";
                context.Database.ExecuteSqlRaw(cmd, product.ProductId);    
                
                product.ThermoformProductCategories = thermoformCategoryIds.Select(catid =>  new ThermoformProductCategory()
                {
                    ProductId = product.ProductId,                       
                    CategoryId = catid,
                    ThermoformCategory = context.ThermoformCategories.Where(i => i.CategoryId == catid).FirstOrDefault()
                }).ToList();

                context.Entry(product).State = EntityState.Modified;                   
                context.SaveChanges();                   
            }
           
        }
    }