Solr DataImportHandler - indexing multiple, related XML documents -

let's have 2 xml document types, , b, this:

a:

<xml>     <a>         <name>first number</name>         <num>1</num>     </a>     <a>         <name>second number</name>         <num>2</num>     </a> </xml> 

b:

<xml>     <b>         <akey>1</akey>         <value>one</value>     </b>     <b>         <akey>2</akey>         <value>two</value>     </b> </xml> 

i'd index this:

<doc>     <str name="name">first name</str>     <int name="num">1</int>     <str name="spoken">one</str> </doc> <doc>     <str name="name">second name</str>     <int name="num">2</int>     <str name="spoken">two</str> </doc> 

so, in effect, i'm trying use value key in b. using dataimporthandler, i've used following data config definition:

<dataconfig>     <datasource type="filedatasource" encoding="utf-8" />     <document>         <entity name="document" transformer="logtransformer" loglevel="trace"             processor="filelistentityprocessor" basedir="/tmp/somedir"             filename="a.*.xml$" recursive="false" rootentity="false"             datasource="null">             <entity name="a"                 transformer="regextransformer,templatetransformer,logtransformer"                 loglevel="trace" processor="xpathentityprocessor" url="${document.fileabsolutepath}"                 stream="true" rootentity="true" foreach="/xml/a">                 <field column="name" xpath="/xml/a/name" />                 <field column="num" xpath="/xml/a/num" />                   <entity name="b" transformer="logtransformer"                     processor="xpathentityprocessor" url="/tmp/somedir/b.xml"                     stream="false" foreach="/xml/b" loglevel="trace">                     <field column="spoken" xpath="/xml/b/value[../akey=${a.num}]" />                 </entity>              </entity>         </entity>     </document> </dataconfig> 

however, encounter 2 problems:

1. i can't xpath expression predicate match rows; regardless of whether use alternative /xml/b[akey=${a.num}]/value, or hardcoded value akey.
2. even when remove predicate, parser goes through b file once every row in a, inefficient.

my question is: how, in light of problems listed above, index data correctly , efficiently dataimporthandler?

i'm using solr 3.6.2 .

note: bit similar this question, deals 2 xml document types instead of rdbms , xml document.

i have bad experiences using dataimporthandler kind of data. simple python script merge data smaller current configuration , more readable. depending on requirements , data size, create temporary xml file or directly pipe results solr. if have use dataimporthandler, use urldatasource , setup minimal server generates xml. obvioulsy i'm python fan, it's quite it's easy job in ruby, perl, ...