Asp.net 核心System.InvalidOperationException: 无法追踪实体类型x的实例

Question

i am kind of newbie at asp.net core and i get a course from udemy. I did everything like instructors did. When i try to add test datas to database i get error that System.InvalidOperationException: 'The instance of entity type 'ProductCategory' cannot be tracked because another instance with the same key value for {'CategoryId', 'ProductId'} is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see the conflicting key values.' System.InvalidOperationException: 'The instance of entity type 'ProductCategory' cannot be tracked because another instance with the same key value for {'CategoryId', 'ProductId'} is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see the conflicting key values.' . I research a lot about that but i understood nothing because it seemed very complicated to me.

SeedDatabase.cs

using Entity.Models;
using Microsoft.EntityFrameworkCore;
using ShopApp.Entity.Models;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace Data.Concrete.EfCore
{
    public static class SeedDatabase
    {
        public static void seed()
        {
            var context = new ShopContext();

            if (context.Database.GetPendingMigrations().Count() == 0)
            {
                if (context.Categories.Count() == 0)
                {
                    context.Categories.AddRange(categories);
                }

                if (context.Products.Count() == 0)
                {
                    context.Products.AddRange(Products);
                    context.AddRange(ProductCategories);
                }
            }
            context.SaveChanges();
        }
        private static Category[] categories = {
            new Category(){Name="Kağıt"},
            new Category(){Name="Kalem"},
            new Category(){Name="Sarf Malzemesi"}
        };

        private static Product[] Products = {
            new Product(){Name="A4 Kağıt",price=11.5,quantity=12,CategoryId=0},
            new Product(){Name="Faber Kalem",price=7,quantity=54,CategoryId=1},
            new Product(){Name="Yazıcı Çarkı",price=3,quantity=87,CategoryId=2},
            new Product(){Name="Dosya Kağıdı",price=0.10,quantity=850,CategoryId=0},
            new Product(){Name="Rotring Kalem",price=16,quantity=125,CategoryId=1},
            new Product(){Name="Toner",price=65,quantity=14,CategoryId=2}
        };
        private static ProductCategory[] ProductCategories = {
            new ProductCategory(){Product=Products[0],Category=categories[0]},
            new ProductCategory(){Product=Products[0],Category=categories[1]},
            new ProductCategory(){Product=Products[1],Category=categories[0]},
            new ProductCategory(){Product=Products[0],Category=categories[1]}
        };
    }
}

Product.cs

namespace ShopApp.Entity.Models
{
    public class Product
    {

        public int Id { get; set; }
        [Required(ErrorMessage ="Lütfen isim giriniz")]
        public string Name { get; set; }
        [Required(ErrorMessage = "Lütfen fiyat giriniz")]
        public double? price { get; set; }
        [Required(ErrorMessage = "Lütfen adet giriniz")]
        public double? quantity { get; set; }
        public string ImageUrl { get; set; }
        [Required(ErrorMessage = "Lütfen kategori seçiniz")]
        public int? CategoryId { get; set; }
        //public Category Category { get; set; }
        public List<ProductCategory> ProductCategories { get; set; }
    }
}

Category.cs

namespace ShopApp.Entity.Models
{
    public class Category
    {        
        public int id { get; set; }
        public string Name { get; set; }
        public string Description { get; set; }
        public List<ProductCategory> ProductCategories { get; set; }
    }
}

ProductCategory.cs

namespace Entity.Models
{
    public class ProductCategory
    {
        public int CategoryId { get; set; }
        public Category Category { get; set; }
        public int ProductId { get; set; }
        public Product Product { get; set; }
    }
}

ShopContext.cs

namespace Data.Concrete.EfCore
{
    public class ShopContext:DbContext
    {
        public DbSet<Product> Products { get; set; }
        public DbSet<Category> Categories { get; set; }
    

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseSqlite("DataSource=ShopDb");
        }
        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<ProductCategory>().HasKey(c => new { c.CategoryId, c.ProductId });
        } 
    }
}

I try to create table that have many to many relations thats means one product may belong many categories and one category may belong many products.

Answer 1

When we change codes that way it works, it throw error because after addrange categories and product, i have to run savechanges() because products and categories have to get id's from database after that we can mark productcategory.

SeedDatabase.cs

namespace Data.Concrete.EfCore
{
    public static class SeedDatabase
    {
        public static void seed()
        {

            var context = new ShopContext();

            if (context.Database.GetPendingMigrations().Count() == 0)
            {

                if (context.Categories.Count() == 0 && context.Products.Count() == 0)
                {
                    var cats = new List<Category> {
                        new Category(){Name="Kağıt"},
                        new Category(){Name="Kalem"},
                        new Category(){Name="Sarf Malzemesi"}
                    };
                    context.Categories.AddRange(cats);



                    context.SaveChanges();
                    var prods = new List<Product>{
                        new Product() { Name = "A4 Kağıt", price = 11.5, quantity = 12, CategoryId = cats[0].id },
                        new Product() { Name = "Faber Kalem", price = 7, quantity = 54, CategoryId = cats[1].id },
                        new Product() { Name = "Yazıcı Çarkı", price = 3, quantity = 87, CategoryId = cats[2].id },
                        new Product() { Name = "Dosya Kağıdı", price = 0.10, quantity = 850, CategoryId =cats[0].id },
                        new Product() { Name = "Rotring Kalem", price = 16, quantity = 125, CategoryId =cats[1].id },
                        new Product() { Name = "Toner", price = 65, quantity = 14, CategoryId = cats[2].id }
                    };
                    context.Products.AddRange(prods);
                    context.SaveChanges();
                    var prodVats = new List<ProductCategory>();
                    for (int i = 0; i < prods.Count; i++)
                    {
                        prodVats.Add(new ProductCategory { CategoryId = prods[i].CategoryId.Value, ProductId = prods[i].Id });
                    }
                    context.AddRange(prodVats);
                    context.SaveChanges();


                }

            }
        }
    
    }
}