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 System.NullReferenceException.

Inheritance
System.Object
TopDocsCollector<T>
TopFieldCollector
TopScoreDocCollector
Inherited Members
System.Object.Equals(System.Object)
System.Object.Equals(System.Object, System.Object)
System.Object.GetHashCode()
System.Object.GetType()
System.Object.MemberwiseClone()
System.Object.ReferenceEquals(System.Object, System.Object)
System.Object.ToString()
Namespace: Lucene.Net.Search
Assembly: Lucene.Net.dll
Syntax
public abstract class TopDocsCollector<T> : ITopDocsCollector, ICollector where T : ScoreDoc
Type Parameters
Name Description
T

Constructors

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TopDocsCollector(PriorityQueue<T>)

Sole constructor.

Declaration
protected TopDocsCollector(PriorityQueue<T> pq)
Parameters
Type Name Description
PriorityQueue<T> pq

Fields

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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
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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>
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m_totalHits

The total number of documents that the collector encountered.

Declaration
protected int m_totalHits
Field Value
Type Description
System.Int32

Properties

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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
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TopDocsCount

The number of valid priority queue entries

Declaration
protected virtual int TopDocsCount { get; }
Property Value
Type Description
System.Int32
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TotalHits

The total number of documents that matched this query.

Declaration
public virtual int TotalHits { get; }
Property Value
Type Description
System.Int32

Methods

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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
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GetTopDocs()

Returns the top docs that were collected by this collector.

Declaration
public virtual TopDocs GetTopDocs()
Returns
Type Description
TopDocs
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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
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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
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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
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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
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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

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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

Extension Methods