Product.cs

public class Product
{
  public int Id { get; set;}
  public decimal UnitPrice{ get; set;}
  public Category Category { get; set;}
}

ProductMap.cs

internal class ProductMap : IEntityTypeConfiguration<Product>
{
    public void Configure(EntityTypeBuilder<Product> builder)
    {
        builder.Property(x => x.Id).HasColumnName("ProductID");
        builder.Property(x=> x.UnitPrice);
        builder.HasOne(x=> x.Category)
            .WithMany(x=> x.Products)
            .HasForeignKey("CategoryID");
    }
}