c# - 转换并合并两个相同接口(interface)但不同类型的列表

Question

我得到了两个使用相同界面的实体。我想将从 Entity Framework 获得的两个结果合并到一个列表 IKurs :

public async Task<IEnumerable<IKurs<ITeacherToCourse<IAdditionalTeacherData>, IAdditionalTeacherData>>> GetCourses(bool takeXtr)
{
    IEnumerable<IKurs<ITeacherToCourse<IAdditionalTeacherData>, IAdditionalTeacherData>> result  = new List<IKurs<ITeacherToCourse<IAdditionalTeacherData>, IAdditionalTeacherData>>();
    if (takeXtr)
        using (var context = new Context())
        {
            var courses = context.XtrCourses.Include(x=>x.TeachersToCourses).Where(_someCourseFilterForAgs);
            result.Concat(await courses.ToListAsync()).Cast<IKurs<ITeacherToCourse<IAdditionalTeacherData>, IAdditionalTeacherData>>();
        }

    using (var context = new Context())
    {
        var courses = context.AgsCourses.Include(x=>x.TeachersToCourses).Where(_someCourseFilterForAgs);
        result.Concat(await courses.ToListAsync()).Cast<IKurs<ITeacherToCourse<IAdditionalTeacherData>, IAdditionalTeacherData>>();
    }
    return result;
}

如您所见，我尝试将它们都与 .Cast<IKurs<ITeacherToCourse<IAdditionalTeacherData>, IAdditionalTeacherData>>() (抛出 InvalidCastException)

这些是我的 Course类，都实现了 IKurs<T1<T2>, T1>但它们的 T1 和 T2 不同(但它们仍然使用相同的接口(interface)):

public class XtrCourse : Core_Xtr_Course, IKurs<XtrTeacherToCourse, XtrAdditionalTeacherData>
{
    public int Nr { get; set; }
    // properties

    public ICollection<XtrTeacherToCourse> TeachersToCourses { get; set; }
}

public class AgsCourse : Core_Ags_Course, IKurs<AgsTeacherToCourse, AgsAdditionalTeacherData>
{
    public int Nr { get; set; }
    // properties

    public ICollection<AgsTeacherToCourse> TeachersToCourses { get; set; }
}

public interface IKurs<TTeacherToCourse, TAdditionalTeacherData>
        where TTeacherToCourse : ITeacherToCourse<TAdditionalTeacherData>
        where TAdditionalTeacherData: IAdditionalTeacherData
{
    int Nr { get; set; }

    ICollection<TTeacherToCourse> TeachersToCourses { get; set; }
}

public interface ITeacherToCourse<T> where T : IAdditionalTeacherData
{
    int Nr { get; set; }
    T AdditionalTeacherData { get; set; }
}

public interface IAdditionalTeacherData
{
    // properties
}

类(class) AgsTeacherToCourse和 XtrTeacherToCourse两者都实现 ITeacherToCourse类(class) AgsTeacherToCourse和 XtrTeacherToCourse两者都实现 ITeacherToCourse

如何将它们合并到一个列表中？

实际上，两个类(class)列表都来自不同的上下文。这就是为什么我在 GetCourses() 中启动上下文两次。

Answer 1

主要问题之一是

interface ITeacherToCourse<T> where T : IAdditionalTeacherData
{
    int Nr { get; set; }
    T AdditionalTeacherData { get; set; }
}

class XtrTeacherToCourse : ITeacherToCourse<XtrAdditionalTeacherData>
{
    public int Nr { get; set; }
    public XtrAdditionalTeacherData AdditionalTeacherData { get; set; }
}

class AgsTeacherToCourse : ITeacherToCourse<AgsAdditionalTeacherData>
{
    public int Nr { get; set; }
    public AgsAdditionalTeacherData AdditionalTeacherData { get; set; }
}

接口(interface)协定定义您只能设置一个值给 XtrAdditionalTeacherData 类型的 AdditionalTeacherData for XtrAdditionalTeacherData 和AgsAdditionalTeacherData 用于 AgsTeacherToCourse。

当我们能够做到时，我们如何才能确保这份契约(Contract)

ITeacherToCourse<IAdditionalTeacherData> ttc = new XtrTeacherToCourse();
ttc.AdditionalTeacherData = new AgsAdditionalTeacherData();

如果您不想设置 AdditionalTeacherData 属性，那么您可以像这样声明接口(interface)

interface ITeacherToCourse<out T> where T : IAdditionalTeacherData
{
    int Nr { get; set; }
    T AdditionalTeacherData { get; }
}

AdditionalTeacherData 现在是readonly 并且T 是一个out T。

现在我们可以

ITeacherToCourse<IAdditionalTeacherData> ttc; 
ttc = new XtrTeacherToCourse();
ttc = new AgsTeacherToCourse();

集合也是一样。

总接口(interface)声明

interface IAdditionalTeacherData
{

}

interface ITeacherToCourse<out T> where T : IAdditionalTeacherData
{
    int Nr { get; set; }
    T AdditionalTeacherData { get; }
}

interface IKurs<out TTeacherToCourse, out TAdditionalTeacherData>
    where TTeacherToCourse : ITeacherToCourse<TAdditionalTeacherData>
    where TAdditionalTeacherData : IAdditionalTeacherData
{
    int Nr { get; set; }
    IEnumerable<TTeacherToCourse> TeachersToCourses { get; }
}

和实现类

class XtrAdditionalTeacherData : IAdditionalTeacherData
{

}

class XtrTeacherToCourse : ITeacherToCourse<XtrAdditionalTeacherData>
{
    public int Nr { get; set; }
    public XtrAdditionalTeacherData AdditionalTeacherData { get; set; }
}

class XtrCourse : IKurs<XtrTeacherToCourse, XtrAdditionalTeacherData>
{
    public int Nr { get; set; }
    public ICollection<XtrTeacherToCourse> TeachersToCourses { get; set; }
    // explicit implementation
    IEnumerable<XtrTeacherToCourse> IKurs<XtrTeacherToCourse, XtrAdditionalTeacherData>.TeachersToCourses => TeachersToCourses;
}

class AgsAdditionalTeacherData : IAdditionalTeacherData
{

}

class AgsTeacherToCourse : ITeacherToCourse<AgsAdditionalTeacherData>
{
    public int Nr { get; set; }
    public AgsAdditionalTeacherData AdditionalTeacherData { get; set; }
}

class AgsCourse : IKurs<AgsTeacherToCourse, AgsAdditionalTeacherData>
{
    public int Nr { get; set; }
    public ICollection<AgsTeacherToCourse> TeachersToCourses { get; set; }
    // explicit implementation
    IEnumerable<AgsTeacherToCourse> IKurs<AgsTeacherToCourse, AgsAdditionalTeacherData>.TeachersToCourses => TeachersToCourses;
}

现在我们可以在不进行任何转换的情况下添加实例

var collection = new List<IKurs<ITeacherToCourse<IAdditionalTeacherData>, IAdditionalTeacherData>>();

collection.Add(new XtrCourse());
collection.Add(new AgsCourse());