LINQ Group by 未按预期返回结果

Question

我有一个动物课：

public class Animals
{
    public string Type { get; set; }
    public string Gender { get; set; }
    public int Amount { get; set; }
}

以及与不同动物相关的成本的类别成本：

public class Cost 
{
    public string AnimalType { get; set; }
    public int Cost { get; set; }
}

我有一个不同类别的列表：

List<Animals> animalList = new List<Animals>()
{
     new Animals() { Type = "Wolf", Gender = "Female", Amount = 10 },
     new Animals() { Type = "Wolf", Gender = "Male", Amount = 20 },
     new Animals() { Type = "Lion", Gender = "Female", Amount = 10 }, 
     new Animals() { Type = "Horse", Gender = "Male", Amount = 5 }
};

List<Cost> cost = new List<Cost>() 
{
    new Cost() { AnimalType = "Wolf", Cost = 1000 },
    new Cost() { AnimalType = "Lion", Cost = 2000 }, 
    new Cost() { AnimalType = "Horse", Cost = 1500 }
}

我想总结每只动物的成本，结果如​​下：

动物类型	成本
狼	30000
狮子	20000
马	7500

我尝试过使用 LINQ 和 sum，如下所示：

var totalCost = from animal in animalList 
      join cost in costList 
      on animal.Type equals cost.AnimalType 
      group animal by animal.Type into g
      select g;

但这只会返回 Wolf （据说是因为它是唯一有两种性别的），但我不明白为什么。我怎样才能写出select找到我要找的东西？

Answer 1

问题是您当前的 LINQ 查询返回数据animal( g)。

相反，在分组时，应该构建一个包含animal和cost数据的新数据集，以便您可以在投影中执行计算。

List<CostModel> costList = new List<CostModel>() 
{
    new CostModel() { AnimalType = "Wolf", Cost = 1000 },
    new CostModel() { AnimalType = "Lion", Cost = 2000 }, 
    new CostModel() { AnimalType = "Horse", Cost = 1500 }
};

var totalCost = (from animal in animalList 
           join cost in costList 
           on animal.Type equals cost.AnimalType 
           group new { Animal = animal, Cost = cost } by animal.Type into g
           select new 
            {
                AnimalType = g.Key,
                Cost = g.Sum(x => x.Cost.Cost * x.Animal.Amount)
            }).ToList();

public class CostModel 
{
    public string AnimalType { get; set; }
    public int Cost { get; set; }
}

虽然您的代码中几乎没有错误：

1. 在LINQ查询中，join cost in costList但是没有声明变量costList。

2. 您将在类中收到错误Cost，因为存在Cost与类名冲突的属性。