将来自 DTO 的数据添加到 db

Question

我有实体和相关的 DTO，它们用于将数据从 DB（实体框架 6）传输到我的 web api 的不同层。代码如下：

    public class Dish
    {
        public int DishId { get; set; }

        [Required]
        [Index(IsUnique = true)]
        [StringLength(400)]
        public string Name { get; set; }

        public string Description { get; set; }

        public double PreparationTime { get; set; }

        public string Photo { get; set; }

        public virtual ICollection<Category> Categories { get; set; } = new List<Category>();

        public virtual ICollection<Ingredient> Ingredients { get; set; } = new List<Ingredient>();

        public virtual ICollection<IngredientAmount> IngredientAmounts { get; set; } = new List<IngredientAmount>();

        public virtual ICollection<RecipeUnit> RecipeUnits { get; set; } = new List<RecipeUnit>();
    }

public class DishDetailedDTO: IDishDTO
    {
        public int DishId { get; set; }

        [Required]
        [StringLength(400)]
        public string Name { get; set; }

        public string Description { get; set; }

        public double PreparationTime { get; set; }

        public string Photo { get; set; }

        public List<CategoryDTO> Categories { get; set; }

        public List<IngredientDetailedDTO> Ingredients { get; set; }

        public List<IngredientAmountDTO> IngredientAmounts { get; set; }

        public List<RecipeUnitDTO> RecipeUnits { get; set; }

    }

public class Category
    {
        public int CategoryId { get; set; }

        [Required]
        [Index(IsUnique = true)]
        [StringLength(20)]
        public string Name { get; set; }

        public virtual ICollection<Dish> Dishes { get; set; } = new List<Dish>();
    }

    public class CategoryDTO: ICategoryDTO
    {
        public int CategoryId { get; set; }

        [Required]
        [StringLength(20)]
        public string Name { get; set; }
    }

当我尝试添加新的 Dish 对象时，问题就出现了，该对象的导航属性（比如说类别）已经存在于数据库中。一般来说，我从某个地方（前端）获取 DishDTO，然后使用 automapper 将其映射到 Dish，然后将此 Dish 添加到上下文中。以下是小规模问题的再现：

        static void Main(string[] args)
        {
            Mapper.Initialize(x=> 
            {
                x.CreateMap<Dish, DishDTO>();
                x.CreateMap<Dish, DishDetailedDTO>();
                x.CreateMap<Dish, DishAvailableIngredientsDTO>();
                x.CreateMap<DishDTO, Dish>();
                x.CreateMap<DishDetailedDTO, Dish>();
                x.CreateMap<DishAvailableIngredientsDTO, Dish>();
                x.CreateMap<Category, CategoryDTO>();
                x.CreateMap<CategoryDTO, Category>();
                x.CreateMap<Ingredient, IngredientDetailedDTO>();
                x.CreateMap<Ingredient, IngredientDTO>();
                x.CreateMap<IngredientDTO, Ingredient>();
                x.CreateMap<IngredientDetailedDTO, Ingredient>();
                x.CreateMap<IngredientAmount, IngredientAmountDTO>();
                x.CreateMap<IngredientAmountDTO, IngredientAmount>();
                x.CreateMap<RecipeUnit, RecipeUnitDTO>();
                x.CreateMap<RecipeUnitDTO, RecipeUnit>();
            });

            var context = new EFDbContext();

            var dish = new DishDetailedDTO()
            {
                Name = "SomeName",
                Categories = new List<CategoryDTO>
                { 
                   new CategoryDTO()
                   {
                       Name = "Breakfast"
                   }
                }
            };

            context.Dishes.Add(Mapper.Map<Dish>(dish));
            context.SaveChanges();

            Console.ReadLine();

        }

那我有异常

SqlException: Cannot insert duplicate key row in object 'dbo.Categories' with unique index 'IX_Name'. The duplicate key value is (Breakfast).
The statement has been terminated.

Answer 1

您的Dish 模型的设计是错误的，一个Dish 可以有多个Categories，而一个Category 可以有多个Dishes，这使得它是多对多关系。要处理这种情况，您需要添加另一个模型，例如：-

public class DishCategoryMapping
{
    public int Id { get; set; }
    public int DishId { get; set; }
    public int CategoryId { get; set; }

    //navigation properties
}

然后你的菜模型看起来像

public class Dish
{
    public int DishId { get; set; }
    public virtual ICollection<DishCategoryMapping> DishCategoryMappings { get; set; }

    //other properties
}

然后，您将为DishCategoryMapping 表中菜肴的每个类别插入一行。