Linq to objects嵌套group-by

Question

我让这个查询起作用了，但是它没有返回我想要的结果。

我收集了以下内容：

List<TransactionRecord> transactionLog;

TransactionRecord简化版看起来像这样：

class TransactionRecord {
   public string txSetComments;
   public string BatchComments;
   public string TargetComments;
   public string TargetName;
   public string TargetValue;
} 

并且可以初始化为：

List<TransactionRecord> transactionLog = new List<TransactionRecord>()
{     
    new TransactionRecord { txSetComments = "txc1", 
                            BatchComments = "bc1",
                            TargetComments = "tc1", 
                            TargetName = "target1",
                            TargetValue = "v1" },

    new TransactionRecord { txSetComments = "txc1",
                            BatchComments = "bc1",
                            TargetComments = "tc1", 
                            TargetName = "target1",
                            TargetValue = "v2" },

    new TransactionRecord { txSetComments = "txc2", 
                            BatchComments = "bc2",
                            TargetComments = "tc1", 
                            TargetName = "target2",
                            TargetValue = "v3" },

    new TransactionRecord { txSetComments = "txc2", 
                            BatchComments = "bc1",
                            TargetComments = "tc1", 
                            TargetName = "target2",
                            TargetValue = "v4" },

    new TransactionRecord { txSetComments = "txc1", 
                            BatchComments = "bc3",
                            TargetComments = "tc1", 
                            TargetName = "target1",
                            TargetValue = "v5" },

    new TransactionRecord { txSetComments = "txc3",     
                            BatchComments = "bc3",
                            TargetComments = "tc1", 
                            TargetName = "target3",
                            TargetValue = "v6" }          
};

以下是到目前为止的查询：

Dictionary<string, Dictionary<string, IEnumerable<TransactionRecord>>> history =
    transactionLog.GroupBy(tx => tx.TxSetComments)
        .ToDictionary(g => g.Key,
                      g => g.GroupBy(b => b.BatchComments).ToDictionary(e => e.Key,
                                                                        e => e.Where(t => t.TargetName == Target)));

这是问题所在。如果我在查询中将“目标”设置为"target1"，大部分结果与我预期的一样：

txc1
   bc1
      target1/v1 
      target1/v2
   bc3
      target1/v5

这是一个很好的开始，但我也得到了：

txc2
txc3

添加到列表中，以获得如下所示的完整结果：

txc1
   bc1
      target1/v1 
      target1/v2
   bc3
      target1/v5
txc2
txc3

我希望查询只返回顶层组，如果有匹配的“目标”。在上面的示例中，它仍然返回"txc2“和"txc3”作为顶层组，即使它们与"Target“不匹配。

我希望这不会太令人困惑。有什么建议吗？

谢谢!

Answer 1

将Where子句复制到GroupBy之外。

var history = transactionLog.Where(record => record.TargetName == "target1")
    .GroupBy(tx => tx.txSetComments)
    .ToDictionary(
        g => g.Key,
        g => g.GroupBy(b => b.BatchComments)
               .ToDictionary(e => e.Key,
                             e => e.Where(t => t.TargetName == "target1"));