Question

我在生产环境的错误日志中收到了此异常：

System.ArgumentException: An item with the same key has already been added
    at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add) 
    at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer)

代码在所有其他环境以及单元测试期间都运行良好。我猜测存在某种多线程问题，但我不知道它会是什么。我想我会得到某种Collection Modified异常，而不是重复的密钥异常。

这不是确切但更简单的例子，代码实际上在做什么：

编辑1

我已经重新定义了如何调用它以及如何存储信息以期回答评论中的一些常见问题......

public LotInfo CallSite(){
    return new LotInfo(new CarLot());
}

public class LotInfo {
    private Dictionary<int,int> SumOfMileageByYear { get; set; }

    public LotInfo(CarLot carLot)
    {
        SumOfMileageByYear = (from c in carLot.Cars
                group c by c.Year into carsByYear
                select new { Year = carsByYear.Key, Sum = carsByYear.Sum(c => c.Mileage) })
            .ToDictionary(c => c.Year, c => c.Sum);

    }
}


public class CarLot
{
    private IEnumerable<Car> _cars;
    public IEnumerable<Car> Cars
    {
        get
        {
            return _cars ?? (_cars = new List<Car>()
            {
                new Car(1984, "Dodge", "Rampage", 40696),
                new Car(2006, "Volkswagen", "Jetta", 42714),
                new Car(2009, "Nissan", "Versa", 53934),
                new Car(2005, "Lincoln", "Town Car", 62381),
                new Car(2008, "Ford", "Focus", 66072),
                new Car(2007, "Toyota", "Yaris", 68163),
                new Car(2009, "Hyundai", "Sonata", 71279),
                new Car(2006, "Ford", "F150", 73463),
                new Car(2005, "Mazda", "RX-8", 75000),
                new Car(2007, "Volkswagen", "Passat", 78490),
                new Car(2010, "Nissan", "Cube", 78505),
                new Car(2008, "Kia", "Sedona", 80874),
                new Car(2006, "Mitsubishi", "Eclipse", 81186),
                new Car(2008, "Ford", "Taurus", 83332),
                new Car(2008, "Pontiac", "G6", 85842),
            });
        }
        set
        {
            _cars = value;
        }
    }
}

public class Car
{
    public int Year { get; set; }
    public int Mileage { get; set; }
    public string Make { get; set; }
    public string Model { get; set; }

    public Car(int year, string make, string model, int mileage)
    {
        Year = year;
        Make = make;
        Model = model;
        Mileage = mileage;
    }
}

调用Example方法，传入CarLot的新实例，检索属性Cars，这是延迟加载的，但返回一个隐式转换为IEnumerable的List。然后Group By方法应该返回带有它的值的单个键。所有延迟执行都由ToDictionary()调用启动。

Group By Linq Query如何生成重复键而不抛出异常，导致ToDicitionary调用失败？

编辑2

这是具有零上下文的实际代码，该示例基本上提供与实际代码相同的上下文，具有更好的清晰度。我添加它只是因为我错过了一些东西。

RepLeadCapTotalByRepRank = (from c in info.RepLeadCaps
                            group c by c.RepRank.Value into byRepTier
                            select new { RepTier = byRepTier.Key, Sum = byRepTier.Sum(v => v.Cap ?? 0) })
                           .ToDictionary(k => k.RepTier, v => v.Sum);

Answer 1

将.ToDictionary(c => c.Year, c => c.Sum);更改为

.ToLookup(c => c.Year, c => c.Sum);

如何通过返回重复键来进行组操作？

编辑1

编辑2

1 个答案: