Class TopDocsCollector<T>

A base class for all collectors that return a TopDocs output. This collector allows easy extension by providing a single constructor which accepts a PriorityQueue<T> as well as protected members for that priority queue and a counter of the number of total hits.

Extending classes can override any of the methods to provide their own implementation, as well as avoid the use of the priority queue entirely by passing null to TopDocsCollector(PriorityQueue<T>). In that case however, you might want to consider overriding all methods, in order to avoid a .

Inheritance

System.Object

TopDocsCollector<T>

TopFieldCollector

TopScoreDocCollector

Implements

ITopDocsCollector

ICollector

Namespace: Lucene.Net.Search

Assembly: Lucene.Net.dll

Syntax

public abstract class TopDocsCollector<T> : object, ITopDocsCollector, ICollector where T : ScoreDoc

Type Parameters

Name	Description
T

Constructors

TopDocsCollector(PriorityQueue<T>)

Sole constructor.

Declaration

protected TopDocsCollector(PriorityQueue<T> pq)

Parameters

Type	Name	Description
PriorityQueue<T>	pq

Fields

EMPTY_TOPDOCS

This is used in case GetTopDocs() is called with illegal parameters, or there simply aren't (enough) results.

Declaration

protected static readonly TopDocs EMPTY_TOPDOCS

Field Value

Type	Description
TopDocs

m_pq

The priority queue which holds the top documents. Note that different implementations of PriorityQueue<T> give different meaning to 'top documents'. Lucene.Net.Search.HitQueue for example aggregates the top scoring documents, while other priority queue implementations may hold documents sorted by other criteria.

Declaration

protected PriorityQueue<T> m_pq

Field Value

Type	Description
PriorityQueue<T>

m_totalHits

The total number of documents that the collector encountered.

Declaration

protected int m_totalHits

Field Value

Type	Description
System.Int32

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(Int32).

Most Lucene Query implementations will visit matching docIDs in order. However, some queries (currently limited to certain cases of BooleanQuery) can achieve faster searching if the 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 abstract bool AcceptsDocsOutOfOrder { get; }

Property Value

Type	Description
System.Boolean

TopDocsCount

The number of valid priority queue entries

Declaration

protected virtual int TopDocsCount { get; }

Property Value

Type	Description
System.Int32

TotalHits

The total number of documents that matched this query.

Declaration

public virtual int TotalHits { get; }

Property Value

Type	Description
System.Int32

Methods

Collect(Int32)

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 CollectionTerminatedException. In this case, the last docs of the current AtomicReaderContext will be skipped and 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(Int32) or Document(Int32) on every hit. Doing so can slow searches by an order of magnitude or more.

Declaration

public abstract void Collect(int doc)

Parameters

Type	Name	Description
System.Int32	doc

GetTopDocs()

Returns the top docs that were collected by this collector.

Declaration

public virtual TopDocs GetTopDocs()

Returns

Type	Description
TopDocs

GetTopDocs(Int32)

Returns the documents in the rage [start .. pq.Count) that were collected by this collector. Note that if start >= pq.Count, an empty TopDocs is returned.

This method is convenient to call if the application always asks for the last results, starting from the last 'page'.

NOTE: you cannot call this method more than once for each search execution. If you need to call it more than once, passing each time a different start, you should call GetTopDocs() and work with the returned TopDocs object, which will contain all the results this search execution collected.

Declaration

public virtual TopDocs GetTopDocs(int start)

Parameters

Type	Name	Description
System.Int32	start

Returns

Type	Description
TopDocs

GetTopDocs(Int32, Int32)

Returns the documents in the rage [start .. start+howMany) that were collected by this collector. Note that if start >= pq.Count, an empty TopDocs is returned, and if pq.Count - start < howMany, then only the available documents in [start .. pq.Count) are returned.

This method is useful to call in case pagination of search results is allowed by the search application, as well as it attempts to optimize the memory used by allocating only as much as requested by howMany.

NOTE: you cannot call this method more than once for each search execution. If you need to call it more than once, passing each time a different range, you should call GetTopDocs() and work with the returned TopDocs object, which will contain all the results this search execution collected.

Declaration

public virtual TopDocs GetTopDocs(int start, int howMany)

Parameters

Type	Name	Description
System.Int32	start
System.Int32	howMany

Returns

Type	Description
TopDocs

NewTopDocs(ScoreDoc[], Int32)

Returns a TopDocs instance containing the given results. If results is null it means there are no results to return, either because there were 0 calls to Collect(Int32) or because the arguments to TopDocs were invalid.

Declaration

protected virtual TopDocs NewTopDocs(ScoreDoc[] results, int start)

Parameters

Type	Name	Description
ScoreDoc[]	results
System.Int32	start

Returns

Type	Description
TopDocs

PopulateResults(ScoreDoc[], Int32)

Populates the results array with the ScoreDoc instances. This can be overridden in case a different ScoreDoc type should be returned.

Declaration

protected virtual void PopulateResults(ScoreDoc[] results, int howMany)

Parameters

Type	Name	Description
ScoreDoc[]	results
System.Int32	howMany

SetNextReader(AtomicReaderContext)

Called before collecting from each AtomicReaderContext. All doc ids in Collect(Int32) will correspond to Reader.

Add DocBase to the current Reader's internal document id to re-base ids in Collect(Int32).

Declaration

public abstract void SetNextReader(AtomicReaderContext context)

Parameters

Type	Name	Description
AtomicReaderContext	context	Next atomic reader context

SetScorer(Scorer)

Called before successive calls to Collect(Int32). Implementations that need the score of the current document (passed-in to Collect(Int32)), should save the passed-in Scorer and call GetScore() when needed.

Declaration

public abstract void SetScorer(Scorer scorer)

Parameters

Type	Name	Description
Scorer	scorer

Implements

ITopDocsCollector

ICollector