Check if KeyValuePair exists with LINQ's FirstOrDefault-优快云博客

本文讨论了如何使用 LINQ 方法检查 Dictionary 对象中是否存在特定值，包括如何验证返回的键值对是否有效，以及替代方法如使用 ContainsValue 和 Any 方法进行值搜索。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

http://stackoverflow.com/questions/793897/check-if-keyvaluepair-exists-with-linqs-firstordefault

问题:

I have a dictionary of type

Dictionary<Guid,int>

I want to return the first instance where a condition is met using

var available = m_AvailableDict.FirstOrDefault(p => p.Value == 0)

However, how do I check if I'm actually getting back a KeyValuePair? I can't seem to use != or == to check against default(KeyValuePair) without a compiler error. There is a similar thread here that doesn't quite seem to have a solution. I'm actually able to solve my particular problem by getting the key and checking the default of Guid, but I'm curious if there's a good way of doing this with the keyvaluepair. Thanks

If you just care about existence, you could use ContainsValue(0) or Any(p => p.Value == 0)instead? Searching by value is unusual for a Dictionary<,>; if you were searching by key, you could use TryGetValue.

One other approach:

       var record = data.Where(p => p.Value == 1) .Select(p => new { Key = p.Key, Value = p.Value }) .FirstOrDefault();

This returns a class - so will be null if not found.