在非泛型方法中转换为泛型类型

Question

我现在在做什么：

void Main()
{
    var command1 = new PersistenceCommand(new MyIntBO());
    var command2 = new PersistenceCommand(new MyGuidBO());
    var command3 = new PersistenceCommand(new PersistentBO());

    Console.WriteLine(command1.ToString());
    Console.WriteLine(command2.ToString());
    Console.WriteLine(command3.ToString());
}

public class PersistenceCommand
{
    public PersistenceCommand(PersistentBO businessObject)
    {
        _businessObject = businessObject;
    }

    public override string ToString()
    {
        string result = _businessObject.GetType().Name;

        var keyed = _businessObject as IPrimaryKeyed<int>;

        if (keyed != null)
        {
            result += " " + keyed.Id.ToString();
        }

        return result;
    }

    private readonly PersistentBO _businessObject;
}

public interface IPrimaryKeyed<out TKey>
{
    TKey Id { get; }
}

public class PersistentBO {}

public class MyIntBO : PersistentBO, IPrimaryKeyed<int>
{
    public int Id { get { return 1008; } }
}

public class MyGuidBO : PersistentBO, IPrimaryKeyed<Guid>
{
    public Guid Id
    {
        get
        {
            return new Guid("6135d49b-81bb-43d4-9b74-dd84c2d3cc29");
        }
    }
}

打印出来：

MyIntBO 1008
我的GuidBO
持久BO

我想打印：

MyIntBO 1008
MyGuidBO 6135d49b-81bb-43d4-9b74-dd84c2d3cc29
持久BO

最优雅的方法是什么？

我想支持所有类型的键 - int、long、Guid 等 - 所以我宁愿不进行多次转换。请注意，并非每个业务对象都实现该接口（有些没有一个主键）。

我意识到我可以使用反射并尝试访问Id 属性。我想知道是否有更好的解决方案。

澄清：为了解决@Acaz Souza 和@Petar Ivanov 的答案，我们有几十个类分散在已经实现IPrimaryKeyed<T> 的多个程序集中。我不想通过扩展接口契约来破坏所有这些。如果我从头开始设计，他们的解决方案会奏效。

Answer 1

只需创建一个非泛型接口并将泛型接口替换为泛型抽象类即可。然后检查接口：

    public interface IPrimaryKeyed
    {
        object ObjId { get; }
    }

    public abstract class PrimaryKeyed<TKey> : IPrimaryKeyed
    {
        public object ObjId { get { return Id; } }
        public abstract TKey Id { get; }
    }

---

public override string ToString()
{
    string result = _businessObject.GetType().Name;

    var keyed = _businessObject as IPrimaryKeyed;

    if (keyed != null)
    {
        result += " " + keyed.ObjId.ToString();
    }

    return result;
}

Answer 2

使用反射似乎不是一个坏方法。

ToString 方法：

// for getting the Id prop
var identProp = _businessObject.GetType().GetProperty("Id");
string result = _businessObject.GetType().Name;

if (identProp != null)
{
    result += " " + identProp.GetValue(_businessObject, null).ToString();
}  

Answer 3

问题出在那一行：

var keyed = _businessObject as IPrimaryKeyed<int>;

你的其他类型不是IPrimaryKeyed<int>是IPrimaryKeyed<Guid>，那么if (keyed != null)是假的。

你可以试试这个：

static void Main()
{
    var command1 = new PersistenceCommand(new MyIntBO());
    var command2 = new PersistenceCommand(new MyGuidBO());
    var command3 = new PersistenceCommand(new PersistentBO());

    Console.WriteLine(command1.ToString());
    Console.WriteLine(command2.ToString());
    Console.WriteLine(command3.ToString());
    Console.ReadLine();
}

public class PersistenceCommand
{
    public PersistenceCommand(PersistentBO businessObject)
    {
        _businessObject = businessObject;
    }

    public override string ToString()
    {
        string result = _businessObject.GetType().Name;

        var keyed = _businessObject as IPrimaryKeyed;

        if (keyed != null)
        {
            result += " " + keyed.Id.ToString();
        }

        return result;
    }

    private readonly PersistentBO _businessObject;
}

public interface IPrimaryKeyed
{
    object Id { get; }
}

public class PersistentBO { }

public class MyIntBO : PersistentBO, IPrimaryKeyed
{
    public object Id { get { return 1008; } }
}

public class MyGuidBO : PersistentBO, IPrimaryKeyed
{
    public object Id { get { return new Guid("6135d49b-81bb-43d4-9b74-dd84c2d3cc29"); } }
}