LINQ Group & Sum on Sum of Models，其中一个属性是另一个模型

// 假设有两个模型：ModelA和ModelB
public class ModelA
{
    public int Id { get; set; }
    public string Name { get; set; }
    public List<ModelB> ModelBs { get; set; }
}

public class ModelB
{
    public int Id { get; set; }
    public int Value { get; set; }
}

// 示例数据
List<ModelA> modelAs = new List<ModelA>
{
    new ModelA
    {
        Id = 1,
        Name = "Group 1",
        ModelBs = new List<ModelB>
        {
            new ModelB { Id = 1, Value = 10 },
            new ModelB { Id = 2, Value = 20 },
            new ModelB { Id = 3, Value = 30 }
        }
    },
    new ModelA
    {
        Id = 2,
        Name = "Group 2",
        ModelBs = new List<ModelB>
        {
            new ModelB { Id = 4, Value = 40 },
            new ModelB { Id = 5, Value = 50 }
        }
    }
};

// 使用LINQ进行分组和求和
var result = modelAs
    .SelectMany(a => a.ModelBs) // 将嵌套的ModelB展开成一个扁平的集合
    .GroupBy(b => b.Id) // 按照ModelB的Id进行分组
    .Select(g => new
    {
        Id = g.Key,
        Sum = g.Sum(b => b.Value) // 对分组后的Value进行求和
    });

// 打印结果
foreach (var item in result)
{
    Console.WriteLine($"Id: {item.Id}, Sum: {item.Sum}");
}