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The following page has been changed by NoblePaul: http://wiki.apache.org/solr/DataImportHandler ------------------------------------------------------------------------------ </dataConfig> }}} - This data-config is the interesting part. If you read the structure of the Slashdot RSS, it has a few header elements such as title, link and subject. Those are mapped to the SOLR fields source, source-link and subject respectively using xpath syntax. The feed also has multiple ''item'' elements which contain the actual news items. + This data-config is the interesting part. If you read the structure of the Slashdot RSS, it has a few header elements such as title, link and subject. Those are mapped to the SOLR fields source, source-link and subject respectively using xpath syntax. The feed also has multiple ''item'' elements which contain the actual news items. So, what we wish to do is , create a document in SOLR for each 'item'. - The ''forEach'' attribute in the slashdot ''entity'' contains xpath which tells DataImportHandler "What are the records that need to be converted into SOLR documents?". As you can see in the data-config, the forEach="/RDF/channel | /RDF/item" specifies two kinds of records separated by '|' (OR in standard xpath lexicon). The first one says "Create a SOLR document for each ''channel'' element". The second one says "Create a SOLR document for each ''item'' element". + The X!PathEntityprocessor is designed to stream the xml, row by row (Think of a row as various fields in a xml element ). It uses the ''forEach'' attribute to identify a 'row'. In this example forEach has the value `'/RDF/channel | /RDF/item'` . This says that this xml has two types of rows (This uses the xpath syntax for OR and there can be more than one type of rows) . After it encounters a row , it tries to read as many fields are there in the field declarations. So in this case, when it reads the row `'/RDF/channel'` it may get 3 fields 'source', 'source-link' , 'source-subject' . After it processes the row it realizes that it does not have any value for the 'pk' field so it does not try to create a SOLR document for this row (Even if it tries it may fail in solr). But all these 3 fields are marked as `commonField="true"` . So it keeps the values handy for subsequent rows. - But ofcourse, it doesn't make sense to create a SOLR document containing only the header elements, right? That's what we thought too, therefore we have the ''pk'' attribute in the slashdot ''entity''. The ''pk=link'' says to DataImportHandler that only if the ''link'' field is present in the record, then only create a SOLR document for that record. Otherwise, just move on to the next one. The Slashdot RSS feed has only one ''/RDF/channel'' element present, therefore there is only record containing the source, source-link and subject fields. Since this record does not contain the ''link'' field (our pk), no SOLR document is created for this record and the !EntityProcessor just moves on. + It moves ahead and encounters `/RDF/item` and processes the rows one by one . It gets the values for all the fields except for the 3 fields in the header. But as they were marked as common fields, the processor puts those fields into the record just before creating the document. - But, we did want to store those header fields, right? Yes, we can do that by adding ''commonField=true'' attribute to the header fields (source, source-link and subject). The ''commonField=true'' says that "store the values for these fields and add them to each SOLR document created". Therefore, when the processor comes to records of ''/RDF/item'' elements which contain our pk, it creates a SOLR document for them and adds the header fields to each such document. + What about this ''transformer=!DateFormatTransformer'' attribute in the entity? This is an inbuilt utility transformer helps the user parse his date strings in custom format to 'Date' objects . Note the field `<field column="date" xpath="/RDF/item/date" dateTimeFormat="yyyy-MM-dd'T'hh:mm:ss" />` . The transformer only applies to a field which has the attribute 'dateTimeFormat' and it uses the syntax of [ http://java.sun.com/j2se/1.4.2/docs/api/java/text/SimpleDateFormat.html java's !SimpleDateFormat]. - What about this ''transformer=!DateFormatTransformer'' attribute in the entity? Date representation is always a problem when getting data. Each data source decides to use it's own format for representing dates but you need to parse it and convert it into a java.util.Date object for SOLR to index into a date field. Therefore, we supply a transformer called !DateFormatTransformer which needs you to supply the input format for the date string and we'll do the rest. It uses java.text.!SimpleDateFormat class internally, so the syntax for dateTimeFormat attribute is the same as you'd write if you were using !SimpleDateFormat class. + You can use this feature for indexing from REST API's such as rss/atom feeds, XML data feeds , other SOLR servers or even well formed xhtml documents . Our XPath support has its limitations but we have tried to make sure that common use-cases are covered and since it's based on a streaming parser, it is extremely fast and consumes constant amount of memory even for large XMLs. Easy, isn't it? And you didn't need to write one line of code! Enjoy :) - You can use this feature for indexing from REST API's such as RSS/Atom feeds, other SOLR servers, XML data feeds or Last.FM user profiles! The possibilities are endless. Our XPath support has its limitations but we have tried to make sure that common use-cases are covered and since it's based on a streaming parser, it is extremely fast and consumes constant amount of memory even for large XMLs. Easy, isn't it? And you didn't need to write one line of code! Enjoy :) - = Extending the tool with APIs = The examples we explored are admittedly, trivial . It is not possible to have all user needs met by an xml configuration alone. So we expose a few interfaces which can be implemented by the user to enhance the functionality.
