LINQ查询-根据具有与字符串匹配的属性的值选择键？

public class Foo { }

public class Bar
{
    public String Prop1 { get; set; }
}

foreach (var kvp in MyDictionary)
{
    if (kvp.Value.Prop1 == theString)
    {
        var key = kvp.Key;
        //Do something with it
        break;
    }
}

foreach (var kvp in MyDictionary.Where(kvp => kvp.Value.Prop1 == theString))
{
    var key = kvp.Key;
    //Do something with it
    //break; is unnecessary because I only get one kvp back anyways.
}

Single

SingleOrDefault

First

var key = MyDictionary.Single(pair => pair.Value.Prop1 == someValue).Key;

Single

SingleOrDefault

var key = MyDictionary.First(kvp => kvp.Value.Prop1 == theString).Key;

// Do this just once: it\'s expensive
var reverseDict = MyDictionary.ToDictionary(kvp => kvp.Value.Prop1, kvp => kvp.Key);

...
// Do this as many times as you need: it\'s cheap
var key = reverseDict[someValue];