请NameValueCollection中接触到LINQ查询 [英] Make NameValueCollection accessible to LINQ Query

问题描述

如何让的NameValueCollection 访问LINQ查询运算符，如在哪里，加盟，GROUPBY？

How to make NameValueCollection accessible to LINQ query operator such as where, join, groupby?

我试过如下：

private NameValueCollection RequestFields()
{
    NameValueCollection nvc = new NameValueCollection()
                                  {
                                      {"emailOption: blah Blah", "true"},
                                      {"emailOption: blah Blah2", "false"},
                                      {"nothing", "false"},
                                      {"nothinger", "true"}
                                  };
    return nvc;

}

public void GetSelectedEmail()
{
    NameValueCollection nvc = RequestFields();
    IQueryable queryable = nvc.AsQueryable();
}

不过，我得到了一个的的ArgumentException 的告诉我，在源不是IEnumerable的＆LT;> 。

推荐答案

您需要的升降机的非通用的IEnumerable 到的IEnumerable＆LT ;字符串＆GT; 。有人建议你使用 OfType 但这是一个过滤方法。你在做什么是一个演员，因为里面是有演员等效操作符：

You need to "lift" the non-generic IEnumerable to an IEnumerable<string>. It has been suggested that you use OfType but that is a filtering method. What you're doing is the equivalent of a cast, for which there is the Cast operator:

var fields = RequestFields().Cast<string>();

由于弗朗斯指出，这只是提供了访问键。你仍然需要索引到集合中的值。这是一个扩展方法来提取 KeyValuePair <​​/ code>■从的NameValueCollection ：

public static IEnumerable<KeyValuePair<string, string>> ToPairs(this NameValueCollection collection)
{
    if(collection == null)
    {
        throw new ArgumentNullException("collection");
    }

    return collection.Cast<string>().Select(key => new KeyValuePair<string, string>(key, collection[key]));
}

编辑：为了响应@Ruben Bartelink的要求，这里是如何访问全套每个键使用 ToLookup 值：

In response to @Ruben Bartelink's request, here is how to access the full set of values for each key using ToLookup:

public static ILookup<string, string> ToLookup(this NameValueCollection collection)
{
    if(collection == null)
    {
        throw new ArgumentNullException("collection");
    }

    var pairs =
        from key in collection.Cast<String>()
        from value in collection.GetValues(key)
        select new { key, value };

    return pairs.ToLookup(pair => pair.key, pair => pair.value);
}

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