使LINQ Query可以访问NameValueCollection

如何使NameValueCollectionLINQ查询运算符可以访问,例如where,join,groupby？

我试过以下:

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();
}

但我得到一个ArgumentException告诉我源不是IEnumerable <>.

你需要的"升降机"的非通用IEnumerable到IEnumerable.有人建议您使用OfType但这是一种过滤方法.你正在做的是相当于一个演员,有Cast运营商:

var fields = RequestFields().Cast();

正如弗兰斯指出的那样,这只能提供对密钥的访问.您仍然需要为值集合索引.这是一个KeyValuePair从以下方法中提取s 的扩展方法NameValueCollection:

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

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

编辑:为响应@Ruben Bartelink的请求,以下是如何使用以下方法访问每个密钥的完整值集ToLookup:

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

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

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

或者,使用C#7.0元组:

public static IEnumerable<(String name, String value)> ToTuples(this NameValueCollection collection)
{
    if(collection == null)
    {
        throw new ArgumentNullException("collection");
    }

    return
        from key in collection.Cast()
        from value in collection.GetValues(key)
        select (key, value);
}

AsQueryable必须采取IEnumerable一个通用的.NameValueCollection工具IEnumerable,这是不同的.

而不是这个:

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

试试OfType(它接受非通用接口)

{
    NameValueCollection nvc = RequestFields();
    IEnumerable canBeQueried = nvc.OfType();
    IEnumerable query =
       canBeQueried.Where(s => s.StartsWith("abc"));
}

字典实际上可能更接近您想要使用的字典,因为它实际上将填充NameValueCollection填充的更多角色.这是Bryan Watts解决方案的变体:

public static class CollectionExtensions
{
    public static IDictionary ToDictionary(this NameValueCollection source)
    {
        return source.Cast().Select(s => new { Key = s, Value = source[s] }).ToDictionary(p => p.Key, p => p.Value); 
    }
}

var fields = RequestFields().AllKeys;

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

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