无法遍历泛型类型 B 的列表 A(icollection)，其中 A 和 B 都实现相同的接口 [英] Cannot loop through list A(icollection) of generic type B where A and B both implement same interface

问题描述

介绍有点乏味，但只是为了清楚起见！有些人甚至可能从中学到一些东西或获得一些方便的见解.我的问题在底部.我真的希望有人能帮助我！

The intro is a bit tedious, but is just for clearity! Some might even learn something from it or get some handy insights. My question is found at the bottom. I really hope someone can help me!

我有这个界面

public interface IEFEntity
{
    object GetPKValue();
    bool PKHasNoValue();
}

我所有的自动生成的 EF 类都实现了这个接口并实现了 2 个方法.这是通过使用部分类的单独文件完成的，因此在重新生成 EF 类时实现不会消失.这对于问题并不重要，但我在下面给出了两个 EF 类的设置示例，debiteur 和 schakeling.所有都在同一个命名空间offcourse:

All my automatic genereted EF classes implement this interface and implement the 2 methods. This is done via a separate file using partial classes so the implementation is not gone when regenerating the EF classes. This is not important for the question but I have put an example of the setup of two EF classes, debiteur and schakeling below. All are in the same namespace offcourse:

public partial class debiteur
    {
        public debiteur()
        {
            this.schakeling = new HashSet<schakeling>();
        }

        public int id { get; set; }
        public string naam { get; set; }

        public virtual ICollection<schakeling> schakeling { get; set; }
    }

public partial class schakeling
    {
        public schakeling()
        {
            this.debiteur = new HashSet<debiteur>();
        }

        public int id { get; set; }
        public string omschrijving { get; set; }

        public virtual ICollection<debiteur> debiteur { get; set; }
    }

我有这两个额外的部分来实现接口.这里没什么特别的.

And I have this 2 extra partials that implement the interface. Nothing special here.

public partial class debiteur : IEFEntity
    {
        public object GetPKValue() {
            return this.id;
        }

        public bool PKHasNoValue() {
            return this.id == 0;
        }
    }

public partial class schakeling : IEFEntity
    {
        public object GetPKValue() {
            return this.id;
        }

        public bool PKHasNoValue() {
            return this.id == 0;
        }
    }

(只是为了澄清:其他 EF 生成的类可能具有名称不是id"的 PK 属性，或者甚至具有字符串类型的 PK 和用户名的名称，但这对于问题并不重要！而且也不是我使用这些方法的唯一原因，请继续阅读...)

我有一个使用两个泛型类型参数的 GenManager 类.这是没有实现的类定义.(而且我知道，这仅适用于具有单个 PK 而非复合键的实体/表，正如争论的那样 这里)

I have a GenManager class which uses two generic type parameters. Here's the class definition without implementation. (And I know, this only works for entities/tables with a single PK not with composite keys, as debated here)

public class GenManager<Entity, EntityKey> where Entity : class, IEFEntity {}

这意味着实体类型参数必须是实现接口 IEFEntity 的类.所以在我的应用程序中的任何地方，假设我现在可以使用以下控制器创建一个实例:

This means that the Entity type parameter must be a class which implement interface IEFEntity. So anywhere in my application, lets say a controller I can now create an instance by using:

private GenManager<debiteur, int> DebiteurManager;
private GenManager<schakeling, int> SchakelingManager;

但例如:

private GenManager<anotherClass, int> AnotherClassManager;

会失败，因为 anotherClass 没有实现 IEFEntity.但是回到 GenManager 类.这是没有所有实现的第一个大纲

will fail because anotherClass does not implement IEFEntity. But back to the GenManager class. Here's the first outlining without all the implementation

public class GenManager<Entity, EntityKey> where Entity : class, IEFEntity
    {
        public IQueryable<Entity> Items { get { return repo.Items; } }
        private IGenRepo<Entity, EntityKey> repo;

        public GenManager(IGenRepo<Entity, EntityKey> repo) { this.repo = repo; }

        public Entity find(EntityKey pk) { return repo.find(pk); }
        public RepoResult delete(EntityKey pk) { return repo.delete(pk); }
        public RepoResult create(Entity item) { return repo.create(item); }
        public RepoResult update(Entity item) { return repo.update(item); }

        public bool isInFKEntity<FKEntity, FKEntityKey>(EntityKey pk, FKEntityKey fk) where FKEntity : class, IEFEntity { }

        public List<FKEntity> GetFKEntities<FKEntity, FKEntityKey>(EntityKey pk) where FKEntity : IEFEntity { }

        public RepoResult removeFKEntities<FKEntity, FKEntityKey>(EntityKey pk, FKEntityKey[] fkList) where FKEntity : IEFEntity { }

        public RepoResult addFKEntities<FKEntity, FKEntityKey>(EntityKey pk, FKEntityKey[] fkList) where FKEntity : IEFEntity { }

        public RepoResult resetFKEntities<FKEntity, FKEntityKey>(EntityKey pk, FKEntityKey[] fkList) where FKEntity : IEFEntity { }

        public RepoResult resetFKEntities2<FKEntity, FKEntityKey>(EntityKey pk, FKEntityKey[] fkList) where FKEntity : IEFEntity { }

        public RepoResult resetFKEntities3<FKEntity, FKEntityKey>(EntityKey pk, FKEntityKey[] fkList) where FKEntity : IEFEntity { }

        public RepoResult clearFKEntities<FKEntity>(EntityKey pk) where FKEntity : IEFEntity { }
    }

花点时间看看这个.正如GenManager 类的第一个泛型类型Entity 必须是一个实现了IEFEntity 的类，这也必须是泛型类型FKEntity 在方法中使用.例如，在我的控制器中，我现在可以使用以下语句:

Take a second to look at this. Just as the first generic type Entity of the GenManager class must be a class that implements IEFEntity, this must also be the case with generic type FKEntity used in the methods. So in my controller for example I can now use this statement:

bool b = DebiteurManager.isInFKEntity<schakeling, int>(debiteur_id, schakeling_id);

还是举个例子:

bool b = DebiteurManager.isInFKEntity<anotherEntity, int>(debiteur_id, anotherEntity_id);

会失败，因为 anotherEntity 没有实现 IEFEntity.

will fail because anotherEntity does not implement IEFEntity.

而正是在这些方法中，必须使用 c# 反射才能产生奇迹，而我面临一个问题.我给你未完成的方法 isInFKEntity 的实现和一些测试代码语句，包括注释:

And it is in these methods where the magic must happen using c# reflection and I face a problem. I give you the implementation of the unfinished method isInFKEntity with some test code statements including comments:

public bool isInFKEntity<FKEntity, FKEntityKey>(EntityKey pk, FKEntityKey fk) where FKEntity : class, IEFEntity
    {
        Entity dbEntry = find(pk);
        if (dbEntry == null) throw new InvalidOperationException(RepoMessages.dbEntryIsNull(new List<object> { pk }));

        //----------Not important for question! Just to clearify things----------\
        var v1 = typeof(Entity).GetProperty("naam").GetValue(dbEntry);//Sets v1 to a string value
        var v1Copy = new debiteur().GetType().GetProperty("naam").GetValue(dbEntry);//Just to test and clearify what the above statement does, vars have the same value!
        //----------End----------\

        var FKEntityList = typeof(Entity).GetProperty(typeof(FKEntity).Name).GetValue(dbEntry);//Gives a list back at runtime, but I can't loop through them
        var FKEntityListCopy = new debiteur().GetType().GetProperty("schakeling").GetValue(dbEntry);//Just to test and clearify what the above statement does, vars have the same value!

        var FKEntityListWithCast = typeof(Entity).GetProperty(typeof(FKEntity).Name).GetValue(dbEntry) as List<FKEntity>;//Gives a NULL value back at runtime, but intellisense!
        var FKEntityListWithCastCopy = new debiteur().GetType().GetProperty("schakeling").GetValue(dbEntry) as List<FKEntity>;//Just to test and clearify what the above statement does, vars have the same value!(also NULL)

        return false;
    }

我想遍历 FKEntityList 但如果我尝试使用 foreach 执行此操作，我会收到一条消息:foreach 语句无法对object"类型的变量进行操作，因为object"不包含'GetEnumerator' 的公共定义.此外，使用智能感知仅显示 4 个标准方法 Equals(object obj)、GetHashCode()、GetType() 和 ToString().见图片

I want to loop through FKEntityList but if I try to do that using a foreach I get a message: foreach statement cannot operate on variables of type 'object' because 'object' does not contain a public definition for 'GetEnumerator'. Also, using intellisense only shows the 4 standard methods Equals(object obj), GetHashCode(), GetType() and ToString(). See image

所以我尝试使用 as List 成功地将它投射并将结果分配给 FKEntityListWithCast，现在我使用 foreach 没有收到错误消息.

So I try to cast it succesfully using as List<FKEntity> and assign the result to FKEntityListWithCast and now I get no error message using a foreach.

所以我想，很好，我只使用这个 return 语句并且它有效:

So I thought, very nice I just use this return statement and it works:

return FKEntityListWithCast.Any(item => item.GetPKValue().ToString() == fk.ToString());    

上面的 return 语句没有给出错误并且一切都编译，但问题是在运行时 FKEntityListWithCast 没有得到值.它保持NULL.所以问题是:

The above return statment doesn't give an error and everything compiles, but the problem is that at runtime the FKEntityListWithCast doesn't get a value. It stays NULL. So the problem is:

在运行时获取值但不能循环:

GETS VALUE at runtime but CANNOT loop through:

var FKEntityList = typeof(Entity).GetProperty(typeof(FKEntity).Name).GetValue(dbEntry);

在运行时获取无值(NULL)但可以循环:

GETS NO VALUE(NULL) at runtime but CAN loop through:

var FKEntityListWithCast = typeof(Entity).GetProperty(typeof(FKEntity).Name).GetValue(dbEntry) as List<FKEntity>;

任何帮助都会非常有用！

Any help would be greatly appiciated!

推荐答案

ICollection<FKEntity> FKEntityList = typeof(Entity).GetProperty(typeof(FKEntity).Name).GetValue(dbEntry) as ICollection<FKEntity>;

还是很无语，没人能回答这个问题

Still a bummer nobody could answer this

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