Class BlockGroupingCollector

BlockGroupingCollector performs grouping with a single pass collector, as long as you are grouping by a doc block field, ie all documents sharing a given group value were indexed as a doc block using the atomic AddDocuments(IEnumerable<IEnumerable<IIndexableField>>, Analyzer) or UpdateDocuments(Term, IEnumerable<IEnumerable<IIndexableField>>, Analyzer) API.

This results in faster performance (~25% faster QPS) than the two-pass grouping collectors, with the tradeoff being that the documents in each group must always be indexed as a block. This collector also fills in TopGroups.totalGroupCount without requiring the separate TermAllGroupsCollector. However, this collector does not fill in the groupValue of each group; this field will always be null.

NOTE: this collector makes no effort to verify the docs were in fact indexed as a block, so it's up to you to ensure this was the case.

See org.apache.lucene.search.grouping for more details including a full code example.

Note

This API is experimental and might change in incompatible ways in the next release.

Inheritance

object

BlockGroupingCollector

Implements

ICollector

Inherited Members

object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.MemberwiseClone()

object.ReferenceEquals(object, object)

object.ToString()

Namespace: Lucene.Net.Search.Grouping

Assembly: Lucene.Net.Grouping.dll

Syntax

public class BlockGroupingCollector : ICollector

Constructors

BlockGroupingCollector(Sort, int, bool, Filter)

Create the single pass collector.

Declaration

public BlockGroupingCollector(Sort groupSort, int topNGroups, bool needsScores, Filter lastDocPerGroup)

Parameters

Type	Name	Description
Sort	groupSort	The Lucene.Net.Search.Sort used to sort the groups. The top sorted document within each group according to groupSort, determines how that group sorts against other groups. This must be non-null, ie, if you want to groupSort by relevance use Lucene.Net.Search.Sort.RELEVANCE.
int	topNGroups	How many top groups to keep.
bool	needsScores	true if the collected documents require scores, either because relevance is included in the withinGroupSort or because you plan to pass true for either GetScores or GetMaxScores to GetTopGroups(Sort, int, int, int, bool)
Filter	lastDocPerGroup	a Lucene.Net.Search.Filter that marks the last document in each group.

Properties

AcceptsDocsOutOfOrder

Return true if this collector does not require the matching docIDs to be delivered in int sort order (smallest to largest) to Collect(int).

Most Lucene Query implementations will visit matching docIDs in order. However, some queries (currently limited to certain cases of Lucene.Net.Search.BooleanQuery) can achieve faster searching if the Lucene.Net.Search.ICollector allows them to deliver the docIDs out of order.

Many collectors don't mind getting docIDs out of order, so it's important to return true here.

Declaration

public virtual bool AcceptsDocsOutOfOrder { get; }

Property Value

Type	Description
bool

Methods

Collect(int)

Called once for every document matching a query, with the unbased document number.

Note: The collection of the current segment can be terminated by throwing a Lucene.Net.Search.CollectionTerminatedException. In this case, the last docs of the current Lucene.Net.Index.AtomicReaderContext will be skipped and Lucene.Net.Search.IndexSearcher will swallow the exception and continue collection with the next leaf.

Note: this is called in an inner search loop. For good search performance, implementations of this method should not call Doc(int) or Document(int) on every hit. Doing so can slow searches by an order of magnitude or more.

Declaration

public virtual void Collect(int doc)

Parameters

Type	Name	Description
int	doc

GetTopGroups(Sort, int, int, int, bool)

Returns the grouped results. Returns null if the number of groups collected is <= groupOffset.

NOTE: This collector is unable to compute the groupValue per group so it will always be null. This is normally not a problem, as you can obtain the value just like you obtain other values for each matching document (eg, via stored fields, via FieldCache, etc.)

Declaration

public virtual ITopGroups<object> GetTopGroups(Sort withinGroupSort, int groupOffset, int withinGroupOffset, int maxDocsPerGroup, bool fillSortFields)

Parameters

Type	Name	Description
Sort	withinGroupSort	The Lucene.Net.Search.Sort used to sort documents within each group. Passing null is allowed, to sort by relevance.
int	groupOffset	Which group to start from
int	withinGroupOffset	Which document to start from within each group
int	maxDocsPerGroup	How many top documents to keep within each group.
bool	fillSortFields	If true then the Comparable values for the sort fields will be set

Returns

Type	Description
ITopGroups<object>

GetTopGroups<TGroupValue>(Sort, int, int, int, bool)

Returns the grouped results. Returns null if the number of groups collected is <= groupOffset.

NOTE: This collector is unable to compute the groupValue per group so it will always be null. This is normally not a problem, as you can obtain the value just like you obtain other values for each matching document (eg, via stored fields, via FieldCache, etc.)

Declaration

public virtual ITopGroups<TGroupValue> GetTopGroups<TGroupValue>(Sort withinGroupSort, int groupOffset, int withinGroupOffset, int maxDocsPerGroup, bool fillSortFields)

Parameters

Type	Name	Description
Sort	withinGroupSort	The Lucene.Net.Search.Sort used to sort documents within each group. Passing null is allowed, to sort by relevance.
int	groupOffset	Which group to start from
int	withinGroupOffset	Which document to start from within each group
int	maxDocsPerGroup	How many top documents to keep within each group.
bool	fillSortFields	If true then the Comparable values for the sort fields will be set

Returns

Type	Description
ITopGroups<TGroupValue>

Type Parameters

Name	Description
TGroupValue	The expected return type for group value

SetNextReader(AtomicReaderContext)

Called before collecting from each Lucene.Net.Index.AtomicReaderContext. All doc ids in Collect(int) will correspond to Lucene.Net.Index.IndexReaderContext.Reader.

Add Lucene.Net.Index.AtomicReaderContext.DocBase to the current Lucene.Net.Index.IndexReaderContext.Reader's internal document id to re-base ids in Collect(int).

Declaration

public virtual void SetNextReader(AtomicReaderContext context)

Parameters

Type	Name	Description
AtomicReaderContext	context	next atomic reader context

SetScorer(Scorer)

Called before successive calls to Collect(int). Implementations that need the score of the current document (passed-in to Collect(int)), should save the passed-in Lucene.Net.Search.Scorer and call scorer.GetScore() when needed.

Declaration

public virtual void SetScorer(Scorer scorer)

Parameters

Type	Name	Description
Scorer	scorer

Implements

Lucene.Net.Search.ICollector