java - 如何使用 Cassandra Java 驱动程序访问带有嵌套映射的列表

Question

我在使用 Cassandra Java Driver 获取包含 map 的列表时遇到问题。

对于以下版本:

List<Map<Integer, Integer>> myList = state.getList(5, TypeTokens.mapOf(Integer.class, Integer.class));

错误如下:

InvalidRequest: Error from server: code=2200 [Invalid query] message="Java source compilation failed: Line 3: TypeTokens cannot be resolved"

对于如下版本:

List<Map<Integer, Integer>> myList = state.getList(5 , Map.class);

错误如下:

InvalidRequest: Error from server: code=2200 [Invalid query] message="Java source compilation failed: Line 3: Type mismatch: cannot convert from List<Map> to List<Map<Integer,Integer>>

对于最后一个版本，如下所示:

List<Map> myList = state.getList(5, Map.class);

编译器不会提示，但是当我执行聚合时，错误如下:

FunctionFailure: Error from server: code=1400 [User Defined Function failure] message="execution of 'my_keyspace.count_min_udf[count_min_udt, int, int, text]' failed: com.datastax.driver.core.exceptions.CodecNotFoundException: Codec not found for requested operation: [frozen<map<int, int>> <-> java.util.Map]"

state 是一个 UDT，定义为:

CREATE TYPE count_min_udt(
  n int,
  m int,
  p bigint,
  hash_a list <bigint>,
  hash_b list <bigint>,
  values list<frozen <map<int, int>>>
);

我用错了吗？我希望得到一些帮助

Answer 1

答案可以在这里找到: https://community.datastax.com/questions/3939/how-can-i-access-nested-collections-with-the-java.html