Question

我有两个参与亲子关系的课程。父类为Country，子类为City：

public partial class Country
{
    public Country()
    {
        this.Cities = new List<City>();
    }

    public int Id { get; set; }
    public string Name { get; set; }
    public string AlphaCodeTwo { get; set; }
    public string AlphaCodeThree { get; set; }
    public Nullable<int> NumericCode { get; set; }
    public string Capital { get; set; }
    public string Nationality { get; set; }
    public Nullable<decimal> CapitalArea { get; set; }
    public Nullable<decimal> CapitalPopulation { get; set; }
    public string Image { get; set; }
    public virtual List<City> Cities { get; set; }
}

public partial class City
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Code { get; set; }
    public Nullable<int> NumericCode { get; set; }
    public virtual Country Country { get; set; }
}

当我使用以下LINQ查询选择City对象时，父类的导航属性为null：

private List<Country> _Country;
var City = _Country.SelectMany(c => c.Cities).OrderBy(ci => ci.Name).ToList();

我得到所有孩子，但没有父母数据。

Answer 1

如果您正在使用Entity Framework，则可以在加载对象时使用.Include()来获取导航属性数据。请注意，它往往会产生一些非常粗糙的查询。

var city = (
    from c in db.Cities.Include(c => c.Country)
    where c.CountryId == CountryId
    orderby c.Name
    select c
).ToList();

选择子对象时，父导航属性为“null”

1 个答案: