Csharp GroupBy()不是'；除非我首先将各个项目加载到内存中，否则不会按预期工作

我有以下问题，我期待着一些结果.但我只得到了一个结果.

var results = await DbContext.Trucks
    .Where(t => t.Departure.HasValue)
    .Select(t => new
    {
        t.Departure!.Value.Year,
        t.Departure!.Value.Month,
        Quantity = t.InboundQuantity + t.ToTransfers.Sum(x => x.Quantity) - t.FromTransfers.Sum(x => x.Quantity)
    })
    .GroupBy(t => new { t.Year, t.Month })
    .ToDictionaryAsync(g => new DateTime(g.Key.Year, g.Key.Month, 1), g => g.Sum(x => x.Quantity));

Results个个

results Count = 1
+ [0]   {[{7/1/2021 12:00:00 AM}, 3842405714]}

如果我重写查询以将所有行加载到内存中，然后进行分组，则会得到预期数量的结果.

var test = DbContext.Trucks
    .Where(t => t.Departure.HasValue)
    .Select(t => new
    {
        t.Departure!.Value.Year,
        t.Departure!.Value.Month,
        Quantity = t.InboundQuantity + t.ToTransfers.Sum(x => x.Quantity) - t.FromTransfers.Sum(x => x.Quantity)
    })
    .ToList();

var test2 = test
    .GroupBy(t => new { t.Year, t.Month })
    .ToDictionary(g => new DateTime(g.Key.Year, g.Key.Month, 1), g => g.Sum(x => x.Quantity));

Results个个

test2   Count = 27
+ [0]   {[{1/1/2022 12:00:00 AM}, 95309170]}
+ [1]   {[{2/1/2022 12:00:00 AM}, 79737674]}
+ [2]   {[{3/1/2022 12:00:00 AM}, 173875538]}
+ [3]   {[{7/1/2021 12:00:00 AM}, 125219196]}
+ [4]   {[{8/1/2021 12:00:00 AM}, 110993954]}
+ [5]   {[{10/1/2021 12:00:00 AM}, 129282632]}
+ [6]   {[{11/1/2021 12:00:00 AM}, 160927222]}
+ [7]   {[{12/1/2021 12:00:00 AM}, 117813444]}
+ [8]   {[{9/1/2021 12:00:00 AM}, 26260420]}
+ [9]   {[{4/1/2022 12:00:00 AM}, 161695966]}
+ [10]  {[{5/1/2022 12:00:00 AM}, 184781001]}
+ [11]  {[{6/1/2022 12:00:00 AM}, 146985217]}
+ [12]  {[{7/1/2022 12:00:00 AM}, 84260160]}
+ [13]  {[{8/1/2022 12:00:00 AM}, 89769875]}
+ [14]  {[{10/1/2022 12:00:00 AM}, 187958697]}
+ [15]  {[{11/1/2022 12:00:00 AM}, 175034225]}
+ [16]  {[{9/1/2022 12:00:00 AM}, 108421771]}
+ [17]  {[{1/1/2023 12:00:00 AM}, 179720773]}
+ [18]  {[{12/1/2022 12:00:00 AM}, 110000415]}
+ [19]  {[{2/1/2023 12:00:00 AM}, 210461751]}
+ [20]  {[{3/1/2023 12:00:00 AM}, 232239876]}
+ [21]  {[{4/1/2023 12:00:00 AM}, 176482465]}
+ [22]  {[{5/1/2023 12:00:00 AM}, 218732769]}
+ [23]  {[{6/1/2023 12:00:00 AM}, 186324324]}
+ [24]  {[{7/1/2023 12:00:00 AM}, 151700649]}
+ [25]  {[{8/1/2023 12:00:00 AM}, 142653374]}
+ [26]  {[{9/1/2023 12:00:00 AM}, 75763156]}

我可能在这里漏掉了一些愚蠢的东西，但我不知道该怎么解释.

为什么第一个查询没有按预期工作？

Update

如果有人好奇，我使用以下语法使这个查询正确工作.请注意，将第二个参数设置为GroupBy()，并对ToDictionaryAsync()调用进行了微小更改.

var results = await query
    .Where(t => t.Departure.HasValue)
    .Select(t => new
    {
        t.Departure!.Value.Year,
        t.Departure!.Value.Month,
        Quantity = t.InboundQuantity + t.ToTransfers.Sum(x => x.Quantity) - t.FromTransfers.Sum(x => x.Quantity)
    })
    .GroupBy(t => new { t.Year, t.Month }, x => x.Quantity)
    .ToDictionaryAsync(g => new DateTime(g.Key.Year, g.Key.Month, 1), g => g.Sum());