使用 Pig 在 XPath 中进行嵌套解析

Posted 2023-04-18

【中文标题】使用 Pig 在 XPath 中进行嵌套解析

【英文标题】：Nested Parsing in XPath using Pig

【发布时间】：2017-01-17 14:40:07

【问题描述】：

我正在尝试使用 pig 解析带有嵌套标签的 xml 文件。我有以下 xml 示例。

  <Document>
    <medicationsInfo>
     <code>10160-0</code>
     <entryInfo> 
        <statusCode>completed</statusCode>
        <startTime>20110729</startTime>
        <endTime>20110822</endTime>
        <strengthValue>24</strengthValue>
        <strengthUnits>h</strengthUnits>
     </entryInfo> 
     <entryInfo>
        <statusCode>completed</statusCode>
        <startTime>20120130</startTime>
        <endTime>20120326</endTime>
        <strengthValue>12</strengthValue>
        <strengthUnits>h</strengthUnits>
     </entryInfo>
     <entryInfo>
        <statusCode>completed</statusCode>
        <startTime>20100412</startTime>
        <endTime>20110822</endTime>
        <strengthValue>8</strengthValue>
        <strengthUnits>d</strengthUnits>
     </entryInfo>  
    </medicationsInfo>
    <ProductInfo>
     <code>10160-0</code>
     <entryInfo> 
        <statusCode>completed</statusCode>
        <startTime>20110729</startTime>
        <endTime>20110822</endTime>
        <strengthValue>24</strengthValue>
        <strengthUnits>h</strengthUnits>
     </entryInfo> 
     <entryInfo>
        <statusCode>completed</statusCode>
        <startTime>20120130</startTime>
        <endTime>20120326</endTime>
        <strengthValue>12</strengthValue>
        <strengthUnits>h</strengthUnits>
     </entryInfo>
     <entryInfo>
        <statusCode>completed</statusCode>
        <startTime>20100412</startTime>
        <endTime>20110822</endTime>
        <strengthValue>8</strengthValue>
        <strengthUnits>d</strengthUnits>
     </entryInfo>  
    </ProductInfo>
   </Document>

我正在编写以下代码以获取药物信息的条目信息结果，但我收到错误。

代码：

Register /home/cloudera/piggybank-0.16.0.jar;
DEFINE XPathAll org.apache.pig.piggybank.evaluation.xml.XPathAll();
DEFINE XPath org.apache.pig.piggybank.evaluation.xml.XPath();
A =  LOAD '/home/cloudera/Parsed_CCD.xml' using org.apache.pig.piggybank.storage.XMLLoader('medicationsInfo/entryInfo') as (x:chararray);
B = FOREACH A GENERATE XPathAll(x, 'statusCode',false,true), XPathAll(x, 'medicationsInfo/code/code',false,true).$0, XPathAll(x,'strengthValue',false,true).$1;
DUMP B;

错误：

[主要] 信息 org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.MapReduceLauncher - 失败的！ [main] 错误 org.apache.pig.tools.grunt.Grunt - 错误 1066：无法打开别名 B 的迭代器

预期输出：

completed 20110729 20110822 24 h
completed 20120130 20120326 12 h
completed 20100412 20110822  8 d

【参考方案1】：

以下代码将产生预期的输出：

Register /home/cloudera/piggybank-0.16.0.jar;

DEFINE XPathAll org.apache.pig.piggybank.evaluation.xml.XPathAll();

--DEFINE XPath org.apache.pig.piggybank.evaluation.xml.XPath();

A =  LOAD 'home/cloudera/Parsed_CCD.xml' 
using org.apache.pig.piggybank.storage.XMLLoader('medicationsInfo') as (x:chararray);

B = FOREACH A GENERATE 
XPathAll(x, 'medicationsInfo/entryInfo/statusCode').$0, 
XPathAll(x, 'medicationsInfo/entryInfo/startTime').$0,
XPathAll(x, 'medicationsInfo/entryInfo/endTime').$0,
XPathAll(x, 'medicationsInfo/entryInfo/strengthValue').$0,
XPathAll(x, 'medicationsInfo/entryInfo/strengthUnits').$0;

C = FOREACH A GENERATE 
XPathAll(x, 'medicationsInfo/entryInfo/statusCode').$1, 
XPathAll(x, 'medicationsInfo/entryInfo/startTime').$1,
XPathAll(x, 'medicationsInfo/entryInfo/endTime').$1,
XPathAll(x, 'medicationsInfo/entryInfo/strengthValue').$1,
XPathAll(x, 'medicationsInfo/entryInfo/strengthUnits').$1;

D = FOREACH A GENERATE 
XPathAll(x, 'medicationsInfo/entryInfo/statusCode').$2, 
XPathAll(x, 'medicationsInfo/entryInfo/startTime').$2,
XPathAll(x, 'medicationsInfo/entryInfo/endTime').$2,
XPathAll(x, 'medicationsInfo/entryInfo/strengthValue').$2,
XPathAll(x, 'medicationsInfo/entryInfo/strengthUnits').$2;


BCD = UNION B,C,D;

DUMP BCD;

【讨论】：

如果我不知道该部分重复的次数怎么办。

我的实际文件有多个 entryInfo 里面的drugsInfo 我如何在那里实现这个逻辑？

那么你必须编写python或java udf来解析你的xml数据然后喂猪

我认为这个问题很常见，你能建议我最好的方法吗？

我正在使用A = LOAD '/home/cloudera/Parsed_CCD.xml' using org.apache.pig.piggybank.storage.XMLLoader('medicationsInfo/entryInfo') as (x:chararray)，我可以先从加载的drugsInfo 中加载medicationsInfo，然后再加载entryinfo 吗？