How to add data to the database when creating?

Question

ASP.NET

Hello, there are 2 models:

public class Service : EntityBase
    {
        public Guid Id { get; set; }
        public override string H1 { get; set; }
        public virtual Category Category { get; set; }
    }

[Owned]
    public class Category : EntityBase
    {
        public Guid Id { get; set; }
    }

I want to make sure that when adding a table, a connection between these models is also created. filled in the field public virtual Category Category { get; set; }
Added to AppDbContext:

public DbSet<Entities.Service> Services { get; set; }
public DbSet<Entities.Category> Categories { get; set; }
        protected override void OnModelCreating(ModelBuilder builder)
        {
            base.OnModelCreating(builder);


            builder.Entity<Entities.Service>(b =>
            {
                b.HasData(new Entities.Service
                {
                    Id = new Guid("666599D8-EAC4-4F43-9F15-B7063C583B76"),
                    Url = "usluga-1",
                    H1 = "Услуга 1"
                });
                b.OwnsOne(x => x.Category).HasData(new Category
                {
                    Id = new Guid("309035C6-9489-41CA-A395-717243880814"),
                    Url = "default",
                    H1 = "По умолчанию",
                });
            });
        }

but when creating the migration, the error
The seed entity for entity type 'Category' cannot be added because there was no value provided for the required property 'ServiceId' is thrown.
I don’t understand what the ServiceId has to do with it if the field is set to an object, in general, how to register a connection?

Answer 1

It was necessary to create an object of an anonymous type so that a value could be written in the CategoryId, while the CategoryId field itself did not need to be created, the model remains the same

builder.Entity<Category>().HasData(new Entities.Category
            {
                Id = new Guid("309035C6-9489-41CA-A395-717243880814"),
                Url = "default",
                H1 = "По умолчанию"
            });
            builder.Entity<Entities.Service>().HasData(new
            {
                Id = new Guid("666599D8-EAC4-4F43-9F15-B7063C583B76"),
                Url = "usluga-1",
                H1 = "Услуга 1",
                CategoryId = new Guid("309035C6-9489-41CA-A395-717243880814")
            });

Answer 2

The connection is indicated either through attributes or through the fluent api, this is easily googled. You have a one-to-many relationship, one service has many categories, so EF will add the ServiceId field to the Category table when creating tables. Apparently, you need to explicitly specify the service id for the data connection there, for this you need to add this field to the Category model.