实体框架核心与多对多关系

Question

我尝试将一个小应用程序迁移到Entity Framework Core但我无法获得多对多的工作关系。 首先是我的Entities

public class Currency : Entity<int>, IMayHaveUser
{
    public string Code { get; set; }
    public string Name { get; set; }
    public string Symbol { get; set; }
    public virtual List<CountryCurrency> CountryCurrencies { get; set; }
    public bool IsUserDefined => User != null;
    [ForeignKey("UserId")]
    public virtual User User { get; set; }
    public long? UserId { get; set; }
}
public class Country : Entity<int>, IMayHaveUser 
{
    public string Iso2Code { get; set; }
    public virtual ICollection<Era> Eras { get; set; }
    public string Name { get; set; }
    public virtual List<CountryCurrency> CountryCurrencies { get; set; }
    [NotMapped]
    public bool IsUserDefined => User != null;
    [ForeignKey("UserId")]
    public virtual User User { get; set; }
    public long? UserId { get; set; }
}
public class CountryCurrency : Entity<Guid>
{
    public int CountryId { get; set; }
    public Country Country { get; set; }
    public int CurrencyId { get; set; }
    public Currency Currency { get; set; }
}

我的DbContext是

  

modelBuilder.Entity（）。HasKey（currency =＆gt; new {   currency.CountryId，currency.CurrencyId}）;       modelBuilder.Entity（）               .HasOne（pt =＆gt; pt.Country）               .WithMany（p =＆gt; p.CountryCurrencies）               .HasForeignKey（pt =＆gt; pt.CountryId）;

    modelBuilder.Entity<CountryCurrency>()
        .HasOne(pt => pt.Currency)
        .WithMany(t => t.CountryCurrencies)
        .HasForeignKey(pt => pt.CurrencyId);

现在当我添加货币时，例如

  Currency currency;
        Country country;
        CountryCurrency countryCurrency;

        currency = new Currency();
        currency.Id = i++;
        currency.User = null;
        currency.Code = "ETB";
        currency.Name = "Ethiopian Birr";
        currency.Symbol = "Br";

        country =
            this._context.Countries.FirstOrDefault(
                country1 => country1.Iso2Code == "ET");

        if (country != null)
        {
            currency.CountryCurrencies = new List<CountryCurrency>();
            countryCurrency = new CountryCurrency();
            countryCurrency.Country = country;
            countryCurrency.Currency = currency;
            currency.CountryCurrencies.Add(countryCurrency);
            this.InitialCurrencies.Add(currency);
        }
        this._context.Currencies.Add(currency);

所以当我现在在我的测试中检索数据时，我得到了这个代码

Country = context.Countries.Include(country => country.CountryCurrencies).First();

我无法获取ID设置的货币，但财产不是......

Answer 1

您还必须包括货币实体，而不仅仅是加入实体

Country = context.Countries
    .Include(country => country.CountryCurrencies)
        .ThenInclude(e => e.Currency)
    .First();