如何在ASP中创建值对象.. Net MVC，实体框架6项目

Question

在我的测试应用程序中有以下类:

public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
{
    public ApplicationDbContext()
        : base("DefaultConnection", throwIfV1Schema: false)
    {
        Database.SetInitializer<ApplicationDbContext>(new MovieContextInitializer());
    }
    public DbSet<Movie> Movies { get; set; }
    public DbSet<Currency> Currencies { get; set; }
    public static ApplicationDbContext Create()
    {
        return new ApplicationDbContext();
    }
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Types<Movie>()
        .Configure(ctc => ctc.Property(m => m.Price.Amount).HasColumnName("MoviePriceAmount"));
        modelBuilder.Types<Movie>()
        .Configure(ctc => ctc.Property(m => m.Price.Currency.Id).HasColumnName("MoviePriceCurrency"));
        base.OnModelCreating(modelBuilder);
    }
}

MovieContextInitializer for init data:

public class MovieContextInitializer : DropCreateDatabaseIfModelChanges<ApplicationDbContext>
{
    protected override void Seed(ApplicationDbContext context)
    {
        var usdCurrency = new Currency {Id = 1, Name = "USD"};
        var euroCurrency = new Currency {Id = 2, Name = "EUR"};
        context.Currencies.Add(usdCurrency);
        context.Currencies.Add(euroCurrency);
        context.Movies.Add(new Movie
        {
            Title = "GhoustBusters",
            Genre = "Comedy",
            ReleaseDate = new DateTime(2016, 9, 10),
            Price = new Money(50, usdCurrency)
        });
        context.Movies.Add(new Movie
        {
            Title = "Matrix",
            Genre = "Action",
            ReleaseDate = new DateTime(2010, 2, 10),
            Price = new Money(40, euroCurrency)
        });
    }
}

我的实体和值对象类:

public class Movie
{
    public int Id { get; set; }
    public string Title { get; set; }
    public DateTime ReleaseDate { get; set; }
    public string Genre { get; set; }
    public Money Price { get; set; }
}
public class Currency
{
    public int Id { get; set; }
    public string Name { get; set; }
}
[ComplexType]
public class Money 
{
    public Money(int amount, Currency currency)
    {
        Amount = amount;
        Currency = currency;
    }
    public int Amount { get; private set; }
    public Currency Currency { get; private set; }
}

当我试图打电话时:

ApplicationDbContext db = new ApplicationDbContext();
var movies = db.Movies.ToList() 

我得到异常:"在模型生成期间检测到一个或多个验证错误:DomainDrivenWeb.Models.Currency: Name:模式中的每个类型名称必须是唯一的。类型名称'Currency'已经定义。".

Answer 1

这里的问题是，您将Currency视为一个ValueObject和一个实体。

这条线

:

modelBuilder.Types<Movie>()
    .Configure(ctc => ctc.Property(m => m.Price.Currency.Id).HasColumnName("MoviePriceCurrency"));

告诉EF, Currency类型是Move实体上隐式的复杂类型——嵌套在Price属性(Money类型)上。这更像是一个ValueObject。

,

public DbSet<Currency> Currencies { get; set; }

告诉EF将其视为实体。

这就是为什么错误信息说Each type name in a schema must be unique. Type name 'Currency' is already defined. -当需要将货币模型设置为实体时，类型名称货币已经在Movie实体上定义为复杂类型。

如果你删除一个或其他这些配置行，错误应该消失-但它不会真正解决你的问题，因为你需要考虑-是Currency在你的领域真正的实体或ValueObject?

Movie有一个类型为Money的Price，它有一个类型为Currency的属性——这种用法暗示它是一个ValueObject。但是这个类有一个Id字段——"identity"的存在意味着它是一个实体。

您需要仔细考虑领域建模和在这些类型中体现的业务流程，以探索应该如何真正对待它。