IQueryable(非通用):缺少 Count 和 Skip ?它适用于 IQueryable<T> [英] IQueryable (non generic) : missing Count and Skip ? it works with IQueryable<T>

问题描述

我有一个扩展方法，有人给我提供了非常有用的方法...它在 IQueryable 上执行 orderby ...但我想要一个普通的 IQueryable(非通用)

i have an extension method which a person was really helpful to give me... it does an orderby on IQueryable ... but i wanted one to do a normal IQueryable (non generic)

这是代码，计数和跳过，我认为缺少.

Here is the code, The count and Skip and i think Take are missing .

   public static IQueryable GetPage(this IQueryable query,
         int page, int pageSize, out int count)
    {
        int skip = (int)((page - 1) * pageSize);

        count = query.Count(); //COUNT DOESN'T EXIST
        return query.Skip(skip).Take((int)pageSize); // NEITHER SKIP
    }

这是它，它完全没有错误.

Here is the and it works perfectly no errors.

    public static IQueryable<T> GetPage<T>(this IQueryable<T> query,
       int page, int pageSize, out int count)
    {
        int skip = (int)((page - 1) * pageSize);

        count = query.Count();
        return query.Skip(skip).Take((int)pageSize);
    }

有什么想法可以解决这个问题吗?我不想更改我的返回类型，因为它可以完美运行，而且我有另一个名为 ToDataTable 的扩展方法，它也可以在非通用 IQueryable 上运行..

Any ideas how i can get around this? I don't want to change my return types as it works perfectly and i have another extension method called ToDataTable and it also functions on a non generic IQueryable ..

有解决办法吗?

提前致谢

编辑

我在现有的 IQueryable 上这样称呼它

I call it like so on an existing IQueryable

 IQueryable<Client> gen = null;
 IQueryable nongen = null;

 var test = gen.GetPage();  //COMPILES!

 var test 1 = non.GetPage(); // Doesn't compile because GETPAGE
                             // for non generic is broken as it has 
                             // invalid methods like COUNT and SKIP etc.

我尝试删除 GetPage 非通用版本，但随后我的非通用 Iqueryable 没有选择扩展名，因为它不是 Iqueryable 而只是 IQueryable

I tried removing the GetPage non generic version but then my non Generic Iqueryable doesn't pickup the extension due to the fact its not a Iqueryable but only an IQueryable

推荐答案

嗯，很简单，那些方法不适用于 IQueryable.如果您查看 Queryable 方法，您将看到它们几乎都基于 IQueryable.

Well, quite simply those methods aren't available for IQueryable. If you look at the Queryable methods you'll see they're almost all based on IQueryable<T>.

如果你的数据源在执行时真的是一个IQueryable，而你只是不知道T是什么，然后您可以通过反射找到它...或者在 C# 4 中，只需使用动态类型:

If your data source will really be an IQueryable<T> at execution time, and you just don't know what T is, then you could find that out with reflection... or in C# 4, just use dynamic typing:

public static IQueryable GetPage(this IQueryable query,
     int page, int pageSize, out int count)
{
    int skip = (int)((page - 1) * pageSize);
    dynamic dynamicQuery = query;
    count = Queryable.Count(dynamicQuery);
    return Queryable.Take(Queryable.Skip(dynamicQuery, skip), pageSize);
}

C# 编译器的动态位会在执行时为您处理T.

The dynamic bit of the C# compiler will take care of working out T for you at execution time.

不过，总的来说，我鼓励您尝试在任何地方使用通用形式 - 它可能会简单得多.

In general though, I'd encourage you to just try to use the generic form everywhere instead - it's likely to be significantly simpler.

这篇关于IQueryable(非通用):缺少 Count 和 Skip ?它适用于 IQueryable<T>的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！