在类错误中找不到列

Question

我正在尝试从Cassandra表中提取某些数据，然后将其写回cassandra中的其他表。

这是我所拥有的：

JavaRDD<MeasuredValue> mvRDD = javaFunctions(sc).cassandraTable("SB1000_47130646", "Measured_Value", mapRowTo(MeasuredValue.class))
  .where (""Time_Key" IN (1601823,1601824)")
  .select("Time_Key","Start_Frequency","Bandwidth", "Power");  

然后我写回一个新表：

javaFunctions(mvRDD).writerBuilder("spark_reports","SB1000_47130646", mapToRow(MeasuredValue.class)).withColumnSelector(someColumns("Time_Key", "Start_Frequency", "Bandwidth", "Power")).saveToCassandra();

我的测量值类如下所示：

public static class MeasuredValue implements Serializable {

public MeasuredValue() { }
public MeasuredValue(Long Time_Key, Double Start_Frequency, Double Bandwidth, Float Power) {
    this.Time_Key = Time_Key;
    this.Start_Frequency = Start_Frequency;
    this.Bandwidth = Bandwidth;
    this.Power = Power;
}
private Long Time_Key;
public Long gettime_key() { return Time_Key; }
public void settime_key(Long Time_Key) { this.Time_Key = Time_Key; }
private Double Start_Frequency;
public Double getstart_frequency() { return Start_Frequency; }
public void setstart_frequency(Double Start_Frequency) { this.Start_Frequency = Start_Frequency; }
private Double Bandwidth;
public Double getbandwidth() { return Bandwidth; }
public void setbandwidth(Double Bandwidth) { this.Bandwidth = Bandwidth; }
private Float Power;    
public Float getpower() { return Power; }
public void setpower(Float Power) { this.Power = Power;
}

我在运行时得到的错误是：

Exception in thread "main" java.lang.IllegalArgumentException: requirement failed: Columns not found in class com.neutronis.spark_reports.Spark_Reports$MeasuredValue: [Time_Key, Start_Frequency, Bandwidth, Power]

Answer 1

我发现这是因为getter/setters在大写字母和变量方面遵循JAVA命名方案。 由于表中的列是驼峰大小写，因此我已将列名称重新配置为适当的全小写命名约定，以便其正常工作。

为了使用大写字母，我不得不使用HashMap：

 HashMap<String,String> colmap = new HashMap<String,String>();
    colmap.put( "start_frequency", "Start_Frequency" );
    colmap.put( "bandwith", "Bandwidth" );
    colmap.put( "power", "Power" );
    RowReaderFactory<MeasuredValue> mapRowTo = mapRowTo(MeasuredValue.class, colmap);