从通用列表中查找项目 [英] Find item from generic list

问题描述

我在从通用列表中获取记录时遇到问题.我已经创建了一个通用函数，可以从任何类型的类中获取记录.下面是示例代码:-

I have a problem in fetching the record from a generic list. I have created a common function from where i want to get the records from any type of class. Below is sample code:-

public void Test<T>(List<T> rEntity) where T : class
{
    object id = 1;
    var result = rEntity.Where(x => x.id == id);
}

请提出建议.预先感谢.

Please suggest. Thanks in advance.

推荐答案

使用类似这样的方法，对于编译器来说，通常的问题是什么是T"?如果它只是一个类，它甚至可以是Jon提到的 StringBuilder 之类的东西，并且不能保证它具有属性'Id'.因此，它甚至无法按现在的方式进行编译.

With method like that a usual question for compiler is 'what is T' ? If it's just a class it could be anything even a StringBuilder as Jon has mentioned and there is no guarantee that it has a property 'Id'. So it won't even compile the way it is right now.

要使其正常运行，我们有两个选择:

To make it work we have two options :

A)更改方法，让编译器知道预期的类型

A) Change the method and let compiler know what type to expect

B)使用反射并使用运行时操作(在可能的情况下最好避免这样做，但在使用第三方库时可能会派上用场).

B) Use reflection and use run-time operations (better avoid this when possible but may come handy when working with 3rd party libraries).

A-接口解决方案:

public interface IMyInterface
{
   int Id {get; set;}
}

public void Test<T>(List<T> rEntity) where T : IMyInterface
{
    object id = 1;
    var result = rEntity.Where(x => x.id == id);
}

B-反射解决方案:

public void Test<T>(List<T> rEntity)
{
    var idProp = typeof(T).GetProperty("Id");
    if(idProp != null)
    {
       object id = 1;
       var result = rEntity.Where(x => idProp.GetValue(x).Equals(id));
    }
}

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