Question

我在Cassandra表格中存储了一张包含地图的地图：

CREATE TABLE reportsdb.report (
    report_id TEXT,
    entity_type TEXT,
    entity_id TEXT,
    parameters MAP<TEXT, FROZEN<MAP<TEXT, INT>>>,
    PRIMARY KEY ((report_id), entity_type, entity_id)
);

存储数据工作正常，没有任何问题。在检索数据时（使用Java和datastax驱动程序）我想做这样的事情：

resultSet.forEach(row -> {
        Map<String, Map> parametersMap = row.getMap("parameters", String.class, Map.class);
// Do something with the parametersMap here...
}

由于我无法获得泛型类的类，我需要定义

Map<String, Map>

并投下那个，当我真的想定义

时

Map<String, Map<String, Integer>>

但是，运行上面的代码时，我得到以下异常：

Caused by: com.datastax.driver.core.exceptions.CodecNotFoundException: Codec not found for requested operation: [map<varchar, int> <-> java.util.Map]
wildfly       |     at com.datastax.driver.core.CodecRegistry.notFound(CodecRegistry.java:741)
wildfly       |     at com.datastax.driver.core.CodecRegistry.createCodec(CodecRegistry.java:594)
wildfly       |     at com.datastax.driver.core.CodecRegistry.findCodec(CodecRegistry.java:558)
wildfly       |     at com.datastax.driver.core.CodecRegistry.maybeCreateCodec(CodecRegistry.java:643)
wildfly       |     at com.datastax.driver.core.CodecRegistry.createCodec(CodecRegistry.java:586)
wildfly       |     at com.datastax.driver.core.CodecRegistry.access$500(CodecRegistry.java:137)
wildfly       |     at com.datastax.driver.core.CodecRegistry$TypeCodecCacheLoader.load(CodecRegistry.java:246)
wildfly       |     at com.datastax.driver.core.CodecRegistry$TypeCodecCacheLoader.load(CodecRegistry.java:232)
wildfly       |     at com.google.common.cache.LocalCache$LoadingValueReference.loadFuture(LocalCache.java:3542)
wildfly       |     at com.google.common.cache.LocalCache$Segment.loadSync(LocalCache.java:2323)
wildfly       |     at com.google.common.cache.LocalCache$Segment.lockedGetOrLoad(LocalCache.java:2286)
wildfly       |     at com.google.common.cache.LocalCache$Segment.get(LocalCache.java:2201)
wildfly       |     at com.google.common.cache.LocalCache.get(LocalCache.java:3953)
wildfly       |     at com.google.common.cache.LocalCache.getOrLoad(LocalCache.java:3957)
wildfly       |     at com.google.common.cache.LocalCache$LocalLoadingCache.get(LocalCache.java:4875)
wildfly       |     at com.datastax.driver.core.CodecRegistry.lookupCodec(CodecRegistry.java:522)
wildfly       |     at com.datastax.driver.core.CodecRegistry.codecFor(CodecRegistry.java:485)
wildfly       |     at com.datastax.driver.core.AbstractGettableByIndexData.codecFor(AbstractGettableByIndexData.java:73)
wildfly       |     at com.datastax.driver.core.AbstractGettableByIndexData.getMap(AbstractGettableByIndexData.java:338)
wildfly       |     at com.datastax.driver.core.AbstractGettableData.getMap(AbstractGettableData.java:26)
wildfly       |     at com.datastax.driver.core.AbstractGettableByIndexData.getMap(AbstractGettableByIndexData.java:327)
wildfly       |     at com.datastax.driver.core.AbstractGettableData.getMap(AbstractGettableData.java:26)
wildfly       |     at com.datastax.driver.core.AbstractGettableData.getMap(AbstractGettableData.java:231)
wildfly       |     at com.ericsson.sm.reports.slaReport.SlaReportDao.lambda$getReportsFromResultSet$2(SlaReportDao.java:111)
wildfly       |     at java.lang.Iterable.forEach(Iterable.java:75)
wildfly       |     at com.ericsson.sm.reports.slaReport.SlaReportDao.getReportsFromResultSet(SlaReportDao.java:105)
wildfly       |     at com.ericsson.sm.reports.common.AbstractDao.getReports(AbstractDao.java:38)
wildfly       |     at com.ericsson.sm.reports.common.AbstractService.getReports(AbstractService.java:65)
wildfly       |     at com.ericsson.sm.reports.slaReport.SlaReportRestService.getDeviceSlaReports(SlaReportRestService.java:49)
wildfly       |     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
wildfly       |     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
wildfly       |     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
wildfly       |     at java.lang.reflect.Method.invoke(Method.java:498)
wildfly       |     at org.jboss.resteasy.core.MethodInjectorImpl.invoke(MethodInjectorImpl.java:140)
wildfly       |     at org.jboss.resteasy.core.ResourceMethodInvoker.invokeOnTarget(ResourceMethodInvoker.java:295)
wildfly       |     at org.jboss.resteasy.core.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:249)
wildfly       |     at org.jboss.resteasy.core.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:236)
wildfly       |     at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:406)
wildfly       |     ... 56 more

由于上述原因，必须实现自定义编解码器似乎有点奇怪。

我错过了一些明显的东西吗？什么是最干净的解决方案？

由于

Answer 1

通过使用类型令牌来修复此问题：

__new__

没有使用自定义编解码器的卡桑德拉地图。可能？

1 个答案: