Class ToParentBlockJoinCollector

Collects parent document hits for a containing one more more BlockJoinQuery clauses, sorted by the specified parent . Note that this cannot perform arbitrary joins; rather, it requires that all joined documents are indexed as a doc block (using or . Ie, the join is computed at index time.

The parent must only use fields from the parent documents; sorting by field in the child documents is not supported.

You should only use this collector if one or more of the clauses in the query is a ToParentBlockJoinQuery. This collector will find those query clauses and record the matching child documents for the top scoring parent documents.

Multiple joins (star join) and nested joins and a mix of the two are allowed, as long as in all cases the documents corresponding to a single row of each joined parent table were indexed as a doc block.

For the simple star join you can retrieve the ITopGroups<TGroupValue> instance containing each ToParentBlockJoinQuery's matching child documents for the top parent groups, using GetTopGroups(ToParentBlockJoinQuery, Sort, Int32, Int32, Int32, Boolean). Ie, a single query, which will contain two or more ToParentBlockJoinQuery's as clauses representing the star join, can then retrieve two or more ITopGroups<TGroupValue> instances.

For nested joins, the query will run correctly (ie, match the right parent and child documents), however, because TopGroups<TGroupValue> is currently unable to support nesting (each group is not able to hold another TopGroups<TGroupValue>), you are only able to retrieve the TopGroups<TGroupValue> of the first join. The TopGroups<TGroupValue> of the nested joins will not be correct.

See http://lucene.apache.org/core/4_8_0/join/ for a code sample.

@lucene.experimental