Question

我有以下模特：其中有多对多关系。

 public class Product
    {
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int Id { get; set; }

        [Required]
        [MaxLength(50)]
        public string Name { get; set; }
        [Required]
        public string Code { get; set; }
        [MaxLength(1000)]
        public string Description { get; set; }
        public string ImageUrl { get; set; }
        [Required]
        public double Price { get; set; }        
        public decimal Cost { get; set; }
        public bool IsActive { get; set; }

        public ICollection<ProductCategory> ProductCategories { get; set; }

    }

public class ProductCategory
    {
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int? Id { get; set; }

        [Required]
        [MaxLength(50)]
        public string Name { get; set; }
        [Required]
        public string Code { get; set; }
        [MaxLength(1000)]
        public string Description { get; set; }
        public string CategoryImgeUrl { get; set; }


        public ICollection<Product> Products { get; set; }

    }

我想在现有类别中添加新产品，但是当我添加新产品时，我也会在不使用现有产品的情况下创建新类别。

public void Add(ProductViewModel vm)
        {
            try
            {

                if (vm.SelectedCategoryIds.Count() != 0)
                {
                    var catList = new List<ProductCategoryViewModel>();
                    foreach (var item in vm.SelectedCategoryIds) {

                        var cat = Context.ProductCategories.Where(c=>c.Id == item).FirstOrDefault();
                        catList.Add(Mapper.Map<ProductCategoryViewModel>(cat));
                    }

                    vm.ProductCategories = catList;

                }
                var model = Mapper.Map<Product>(vm);
                model.CreatedDate = DateTime.Now;
                model.IsDeleted = false;
                Context.Products.Add(model);
                Context.SaveChanges();
            }
            catch (Exception ex)
            {

            }
        }

在这里，我想添加包含现有类别的新产品。我该如何解决这个问题？

Answer 1

根据您的实体，Product和ProductCategory类创建了多对多的关系。在ProductCategory中尝试此操作并检查

试试这个：

ExternalLoginCallback

Answer 2

可能是

public void Add(ProductViewModel vm)
    {
        try {
            var model = Mapper.Map<Product>(vm);
            model.ProductCategories = new List<ProductCategory>();
                //but this should be done by the Product ctor
            if (vm.SelectedCategoryIds.Count() != 0) {
                //var catList = new List<ProductCategoryViewModel>();
                foreach (var item in vm.SelectedCategoryIds) {
                    var cat = Context.ProductCategories.Where(c=>c.Id == item).FirstOrDefault();
                    if ( cat != null )
                        model.ProductCategories.Add(cat);
                    //catList.Add(Mapper.Map<ProductCategoryViewModel>(cat));
                }
                //vm.ProductCategories = catList;
            }
            //var model = Mapper.Map<Product>(vm);
            model.CreatedDate = DateTime.Now;
            model.IsDeleted = false;
            Context.Products.Add(model);
            Context.SaveChanges();
        }
        catch (Exception ex)
        {

        }
    }

请注意不要将foreach替换为单个查询

foreach (var item in Context.ProductCategories.
    Where(c=> vm.SelectedCategoryIds.Contains(c.Id))) 
{
    model.ProductCategories.Add(item);
}

当然，正如Gert Arnold所建议的那样，有许多变体，例如使用Attach ....

添加新条目实体框架多对多关系映射

2 个答案: