Good day.

I create a database on the principle of Code-first. I have the following classes:

public class Product { public int Id { get; set; } public string Name { get; set; } public int? OrderId { get; set; } public Order Order { get; set; } } public class Order { public int Id { get; set; } public string Customer { get; set; } public ICollection<Product> Product { get; set; } public Order() { Product = new List<Product>(); } } class UserContext : DbContext { public UserContext() : base("DbConnection"){ } public virtual DbSet<Order> Orders { get; set; } public virtual DbSet<Product> Products { get; set; } }

I create objects, write to the database.

By the way - the base - (localdb) \ v11.0 in the file .mdf (roughly speaking the first time I work with EF).

 static void Main(string[] args) { using (UserContext db = new UserContext()) { // AddToDataBase(db); // получаем объекты из бд и выводим на консоль Console.Clear(); var orders = db.Orders.ToList(); foreach (var order in orders) { Console.ForegroundColor = ConsoleColor.Green; Console.WriteLine("{0}.{1}", order.Id, order.Customer); if (order.Product.Count > 1) { Console.ForegroundColor = ConsoleColor.Yellow; foreach (var pr in dp.Product) { Console.WriteLine("{0}.{1}", pr.Id, pr.Name); } } } } Console.Read(); } private static void AddToDataBase(UserContext db) { var pr1 = new Product() { Name = "phone" }; var pr2 = new Product() { Name = "car" }; db.Products.Add(pr1); db.Products.Add(pr2); db.SaveChanges(); var ord1 = new Order() { Customer = "Denis", Product = new Collection<Product>() { pr1 } }; var ord2 = new Order() { Customer = "test", Product = new Collection<Product>() { pr2 } }; Console.WriteLine("Объекты созданы."); db.Orders.Add(ord1); db.Orders.Add(ord2); db.SaveChanges(); Console.WriteLine("Объекты успешно сохранены"); }

I do work by example.

After the first run, I execute the AddToDataBase method. During the second run, I just want to display the data read from the database. But in the end, it deduces that each Order is within the collection of Product 0 items.

Tell me, please, where to look and how to solve?

Thought to change the structure, but will it be correct?

    2 answers 2

    if you use the code first approach, then the virtual access modifier must be set on the navigation properties public virtual Order Order {get;set;}

    In this case, you will be able to get the value from the related table when accessing the navigation property, otherwise you need to tell ef about the need to load the related entities using the Include() or Load() methods

    In the class describing the context of DbSet , the virtual access modifier is not needed. about possible ways to get related entities in a little more detail you can see in my answer

       var orders = db.Orders.Include("Product").ToList();

      If you believe this answer then:

      If DbSet<> marked as virtual , in this case, when executing .ToList() in the data of related objects will be null . To fill them, you need to force .Include() .

      • Hmm, thanks, I will not try - I know what will work. But is that right? And about virtual - previously wrote without it - there was a similar problem. - bodynar
      • as far as I know the virtual access modifier should be at the navigation property - Bald