This module supports index-time joins while searching, where joined + documents are indexed as a single document block using + {@link org.apache.lucene.index.IndexWriter#addDocuments}. This is useful for any normalized content (XML documents or database tables). In database terms, all rows for all + joined tables matching a single row of the primary table must be + indexed as a single document block, with the parent document + being last in the group.
+ +When you index in this way, the documents in your index are divided + into parent documents (the last document of each block) and child + documents (all others). You provide a {@link org.apache.lucene.search.Filter} that identifies the + parent documents, as Lucene does not currently record any information + about doc blocks.
+ +At search time, use {@link org.apache.lucene.search.join.BlockJoinQuery} to remap + matches from any child {@link org.apache.lucene.search.Query} (ie, a query that matches only + child documents) up to the parent document space. The resulting + {@link org.apache.lucene.search.join.BlockJoinQuery} can then be used as a clause in any query that + matches parent documents.
+ +If you only care about the parent documents matching the query, you + can use any collector to collect the parent hits, but if you'd also + like to see which child documents match for each parent document, + use the {@link org.apache.lucene.search.join.BlockJoinCollector} to collect the hits. Once the + search is done, you retrieve a {@link + org.apache.lucene.search.grouping.TopGroups} instance from the + {@link org.apache.lucene.search.join.BlockJoinCollector#getTopGroups} method.
+ + +