如何创建字典字典...？

Question

想象一下，我有一个数据库，其中包含一个或多个表，其中包含一个或多个列的多个索引...

我想创建并填充一个Dictionary<string, Dictionary<string, List<string>>>，这样我就可以获得特定表的所有索引或表和索引的特定组合的所有列。

这里是带有表名、索引名和列名的元组（示例数据）

List<Tuple<string, string, string>> tuples = new List<Tuple<string, string, string>>();
tuples.Add(Tuple.Create("T1", "I1", "C1"));
tuples.Add(Tuple.Create("T1", "I1", "C2"));
tuples.Add(Tuple.Create("T1", "I1", "C3"));
tuples.Add(Tuple.Create("T1", "I2", "C1"));
tuples.Add(Tuple.Create("T2", "I1", "C1"));
tuples.Add(Tuple.Create("T3", "I1", "C1"));
tuples.Add(Tuple.Create("T3", "I1", "C2"));
tuples.Add(Tuple.Create("T3", "I2", "C1"));
tuples.Add(Tuple.Create("T3", "I2", "C2"));
tuples.Add(Tuple.Create("T3", "I2", "C3"));

我能想到的最好的是：

Dictionary<string, Dictionary<string, List<string>>> perTI = new Dictionary<string, Dictionary<string, List<string>>>();
foreach (var group in tuples.GroupBy(x => Tuple.Create(x.Item1, x.Item2)))
{
    perTI[group.Key.Item1] = new Dictionary<string, List<string>>(){ { group.Key.Item2, group.Select(g => g.Item3).ToList() } };
}

有谁知道用 1 条 LINQ 语句来做这件事的方法吗？

Answer 1

只要您愿意，就在一行中：

Dictionary<string, Dictionary<string, List<string>>> dict =
    new List<Tuple<string, string, string>>().GroupBy(item => item.Item1)
        .ToDictionary(
            groupedByItem1 => groupedByItem1.Key,
            groupedByItem1 =>
            groupedByItem1.GroupBy(item => item.Item2)
                .ToDictionary(
                    groupedByItem2 => groupedByItem2.Key,
                    groupedByItem2 => groupedByItem2.Select(item => item.Item3).ToList()));