c# - 无法使用DataStax C# Drive将cassandra中的 "Set"转换为c#中的 "SortedSet"或 "HashSet"

Question

Cassandra表格列如下:

CREATE TABLE mine.testtable (
    id int,
    listtext text,
    myid int,
    name text,
    name1 int,
    setint set<int>,
    stringtext text,
    testlist list<int>,
    testmap map<int, text>,
    testset set<text>,
    textlist list<text>,
    PRIMARY KEY (id)
) WITH read_repair_chance = 0.0
   AND dclocal_read_repair_chance = 0.1
   AND gc_grace_seconds = 864000
   AND bloom_filter_fp_chance = 0.01
   AND caching = { 'keys' : 'ALL', 'rows_per_partition' : 'NONE' }
   AND comment = ''
   AND compaction = { 'class' : 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy' }
   AND compression = { 'sstable_compression' : 'org.apache.cassandra.io.compress.LZ4Compressor' }
   AND default_time_to_live = 0
   AND speculative_retry = '99.0PERCENTILE'
   AND min_index_interval = 128
   AND max_index_interval = 2048;

在 C# 中，getColumnValue函数返回 Cassandra 的一列排。该列可以有任何 Type .我的功能是这样的:

public Object getColumnValue(string tableName, string columnName, int id)
{
    string tmp = string.Format("SELECT {0} FROM {1} WHERE id={2};", columnName ,tableName, id.ToString());
    Row row = Session.Execute(tmp).GetRows().First();
    return row.GetValue(row.GetType(), columnName);
}

可以像这样为不同的列名调用函数:

 SortedDictionary<int, string> dictionary =(SortedDictionary<int, string>)getColumnValue("testtable", "testmap", 3);
 List<string> text =(List<string>)getColumnValue("testtable", "textlist", 2);
 SortedSet<int> setext = (SortedSet<int>)getColumnValue("testtable", "setint", 2);

当我尝试施放 setint 时类型为 set<int>至 SortedSet<int>或 HashSet<int>我收到如下错误:

An unhandled exception of type 'System.InvalidCastException' occurred in Service.exe

Additional information: Unable to cast object of type System.Collections.Generic.List1[System.Int32] to type System.Collections.Generic.SortedSet`1[System.Int32].

考虑到我的 setint是set<int>而不是 list<int> , 为什么我会得到这个异常？

Answer 1

您应该使用通用的 Row.GetValue<T>(columnName)方法:

SortedSet<int> setValue = row.GetValue<SortedSet<int>>("setint");
List<int> listValue = row.GetValue<List<int>>("listint");