Package org.apache.lucene.search.join
Index-time joins
The index-time joining support joins while searching, where joined
documents are indexed as a single document block using
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 BitSetProducer
that identifies the
parent documents, as Lucene does not currently record any information
about doc blocks.
At search time, use ToParentBlockJoinQuery
to remap/join
matches from any child Query
(ie, a
query that matches only child documents) up to the parent document
space. The
resulting query can then be used as a clause in any query that
matches parent.
If you care about what child documents matched for each parent document,
then use the ParentChildrenBlockJoinQuery
query to
per matched parent document retrieve the child documents that caused to match the
parent document in first place. This query should be used after your main query
has been executed. For each hit execute the the
ParentChildrenBlockJoinQuery
query
TopDocs results = searcher.search(mainQuery, 10); for (int i = 0; i < results.scoreDocs.length; i++) { ScoreDoc scoreDoc = results.scoreDocs[i]; // Run ParentChildrenBlockJoinQuery to figure out the top matching child docs: ParentChildrenBlockJoinQuery parentChildrenBlockJoinQuery = new ParentChildrenBlockJoinQuery(parentFilter, childQuery, scoreDoc.doc); TopDocs topChildResults = searcher.search(parentChildrenBlockJoinQuery, 3); // Process top child hits... }
To map/join in the opposite direction, use ToChildBlockJoinQuery
. This wraps
any query matching parent documents, creating the joined query
matching only child documents.
Query-time joins
The query time joining is index term based and implemented as two pass search. The first pass collects all the terms from a fromField that match the fromQuery. The second pass returns all documents that have matching terms in a toField to the terms collected in the first pass.
Query time joining has the following input:
fromField
: The from field to join from.fromQuery
: The query executed to collect the from terms. This is usually the user specified query.multipleValuesPerDocument
: Whether the fromField contains more than one value per documentscoreMode
: Defines how scores are translated to the other join side. If you don't care about scoring useScoreMode.None
mode. This will disable scoring and is therefore more efficient (requires less memory and is faster).toField
: The to field to join to
Basically the query-time joining is accessible from one static method. The user of this method supplies the method
with the described input and a IndexSearcher
where the from terms need to be collected from. The returned
query can be executed with the same IndexSearcher
, but also with another IndexSearcher
.
Example usage of the JoinUtil.createJoinQuery()
:
String fromField = "from"; // Name of the from field boolean multipleValuesPerDocument = false; // Set only to true in the case when your fromField has multiple values per document in your index String toField = "to"; // Name of the to field ScoreMode scoreMode = ScoreMode.Max; // Defines how the scores are translated into the other side of the join. Query fromQuery = new TermQuery(new Term("content", searchTerm)); // Query executed to collect from values to join to the to values Query joinQuery = JoinUtil.createJoinQuery(fromField, multipleValuesPerDocument, toField, fromQuery, fromSearcher, scoreMode); TopDocs topDocs = toSearcher.search(joinQuery, 10); // Note: toSearcher can be the same as the fromSearcher // Render topDocs...
-
Interface Summary Interface Description BitSetProducer A producer ofBitSet
s per segment. -
Class Summary Class Description BlockJoinSelector Select a value from a block of documents.CheckJoinIndex Utility class to check a block join index.JoinUtil Utility for query time joining.ParentChildrenBlockJoinQuery A query that returns all the matching child documents for a specific parent document indexed together in the same block.QueryBitSetProducer ABitSetProducer
that wraps a query and caches matchingBitSet
s per segment.SeekingTermSetTermsEnum A filtered TermsEnum that uses a BytesRefHash as a filterToChildBlockJoinQuery Just likeToParentBlockJoinQuery
, except this query joins in reverse: you provide a Query matching parent documents and it joins down to child documents.ToParentBlockJoinQuery This query requires that you index children and parent docs as a single block, using theIndexWriter.addDocuments()
orIndexWriter.updateDocuments()
API.ToParentBlockJoinSortField A special sort field that allows sorting parent docs based on nested / child level fields. -
Enum Summary Enum Description BlockJoinSelector.Type Type of selection to perform.ScoreMode How to aggregate multiple child hit scores into a single parent score.