Class FieldComparer<T>

Expert: a FieldComparer compares hits so as to determine their sort order when collecting the top results with TopFieldCollector. The concrete public FieldComparer classes here correspond to the SortField types.

This API is designed to achieve high performance sorting, by exposing a tight interaction with FieldValueHitQueue as it visits hits. Whenever a hit is competitive, it's enrolled into a virtual slot, which is an int ranging from 0 to numHits-1. The FieldComparer is made aware of segment transitions during searching in case any internal state it's tracking needs to be recomputed during these transitions.

A comparer must define these functions:

Compare(int, int) Compare a hit at 'slot a' with hit 'slot b'.
SetBottom(int)This method is called by FieldValueHitQueue to notify the FieldComparer of the current weakest ("bottom") slot. Note that this slot may not hold the weakest value according to your comparer, in cases where your comparer is not the primary one (ie, is only used to break ties from the comparers before it).
CompareBottom(int)Compare a new hit (docID) against the "weakest" (bottom) entry in the queue.
SetTopValue(T)This method is called by TopFieldCollector to notify the FieldComparer of the top most value, which is used by future calls to CompareTop(int).
CompareTop(int)Compare a new hit (docID) against the top value previously set by a call to SetTopValue(T).
Copy(int, int)Installs a new hit into the priority queue. The FieldValueHitQueue calls this method when a new hit is competitive.
SetNextReader(AtomicReaderContext)Invoked when the search is switching to the next segment. You may need to update internal state of the comparer, for example retrieving new values from the IFieldCache.
GetValue(int)Return the sort value stored in the specified slot. This is only called at the end of the search, in order to populate Fields when returning the top results.

Note

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

Inheritance

object

FieldComparer

FieldComparer<T>

FieldComparer.DocComparer

FieldComparer.NumericComparer<TNumber>

FieldComparer.RelevanceComparer

FieldComparer.TermOrdValComparer

FieldComparer.TermValComparer

Inherited Members

FieldComparer.SetScorer(Scorer)

object.Equals(object)

object.Equals(object, object)

object.GetHashCode()

object.GetType()

object.MemberwiseClone()

object.ReferenceEquals(object, object)

object.ToString()

Namespace: Lucene.Net.Search

Assembly: Lucene.Net.dll

Syntax

public abstract class FieldComparer<T> : FieldComparer where T : class

Type Parameters

Name	Description
T

Properties

this[int]

Return the actual value in the slot. LUCENENET NOTE: This was value(int) in Lucene.

Declaration

public abstract T this[int slot] { get; }

Parameters

Type	Name	Description
int	slot	The value

Property Value

Type	Description
T	Value in this slot

Methods

Compare(int, int)

Compare hit at slot1 with hit at slot2.

Declaration

public override abstract int Compare(int slot1, int slot2)

Parameters

Type	Name	Description
int	slot1	first slot to compare
int	slot2	second slot to compare

Returns

Type	Description
int	any N < 0 if `slot2`'s value is sorted after `slot1`, any N > 0 if the `slot2`'s value is sorted before `slot1` and 0 if they are equal

Overrides

FieldComparer.Compare(int, int)

CompareBottom(int)

Compare the bottom of the queue with this doc. This will only invoked after SetBottom(int) has been called. This should return the same result as Compare(int, int) as if bottom were slot1 and the new document were slot 2.

For a search that hits many results, this method will be the hotspot (invoked by far the most frequently).

Declaration

public override abstract int CompareBottom(int doc)

Parameters

Type	Name	Description
int	doc	Doc that was hit

Returns

Type	Description
int	Any N < 0 if the doc's value is sorted after the bottom entry (not competitive), any N > 0 if the doc's value is sorted before the bottom entry and 0 if they are equal.

Overrides

FieldComparer.CompareBottom(int)

CompareTop(int)

Compare the top value with this doc. This will only invoked after SetTopValue(T) has been called. This should return the same result as Compare(int, int) as if topValue were slot1 and the new document were slot 2. This is only called for searches that use SearchAfter (deep paging).

Declaration

public override abstract int CompareTop(int doc)

Parameters

Type	Name	Description
int	doc	Doc that was hit

Returns

Type	Description
int	Any N < 0 if the doc's value is sorted after the bottom entry (not competitive), any N > 0 if the doc's value is sorted before the bottom entry and 0 if they are equal.

Overrides

FieldComparer.CompareTop(int)

CompareValues(object, object)

Returns -1 if first is less than second. Default implementation to assume the type implements IComparable<T> and invoke CompareTo(T); be sure to override this method if your FieldComparer's type isn't a IComparable<T> or if you need special null handling.

Declaration

public override int CompareValues(object first, object second)

Parameters

Type	Name	Description
object	first
object	second

Returns

Type	Description
int

Overrides

FieldComparer.CompareValues(object, object)

Exceptions

Type	Condition
ArgumentException	`first` or `second` does not derive from `T` and is not `null`.

CompareValues(T, T)

Returns -1 if first is less than second. Default implementation to assume the type implements IComparable<T> and invoke CompareTo(T); be sure to override this method if your FieldComparer<T>'s type isn't a IComparable<T> or if you need special null handling.

Declaration

public virtual int CompareValues(T first, T second)

Parameters

Type	Name	Description
T	first
T	second

Returns

Type	Description
int

Copy(int, int)

This method is called when a new hit is competitive. You should copy any state associated with this document that will be required for future comparisons, into the specified slot.

Declaration

public override abstract void Copy(int slot, int doc)

Parameters

Type	Name	Description
int	slot	Which slot to copy the hit to
int	doc	DocID relative to current reader

Overrides

FieldComparer.Copy(int, int)

GetValue(int)

Return the actual value in the slot. LUCENENET NOTE: This was value(int) in Lucene.

Declaration

public override object GetValue(int slot)

Parameters

Type	Name	Description
int	slot	The value

Returns

Type	Description
object	Value in this slot

Overrides

FieldComparer.GetValue(int)

SetBottom(int)

Set the bottom slot, ie the "weakest" (sorted last) entry in the queue. When CompareBottom(int) is called, you should compare against this slot. This will always be called before CompareBottom(int).

Declaration

public override abstract void SetBottom(int slot)

Parameters

Type	Name	Description
int	slot	the currently weakest (sorted last) slot in the queue

Overrides

FieldComparer.SetBottom(int)

SetNextReader(AtomicReaderContext)

Set a new AtomicReaderContext. All subsequent docIDs are relative to the current reader (you must add docBase if you need to map it to a top-level docID).

Declaration

public override abstract FieldComparer SetNextReader(AtomicReaderContext context)

Parameters

Type	Name	Description
AtomicReaderContext	context	Current reader context

Returns

Type	Description
FieldComparer	The comparer to use for this segment; most comparers can just return "this" to reuse the same comparer across segments

Overrides

FieldComparer.SetNextReader(AtomicReaderContext)

Exceptions

Type	Condition
IOException	If there is a low-level IO error

SetTopValue(T)

Record the top value, for future calls to CompareTop(int). This is only called for searches that use SearchAfter (deep paging), and is called before any calls to SetNextReader(AtomicReaderContext).

Declaration

public abstract void SetTopValue(T value)

Parameters

Type	Name	Description
T	value

SetTopValue<TValue>(TValue)

Record the top value, for future calls to CompareTop(int). This is only called for searches that use SearchAfter (deep paging), and is called before any calls to SetNextReader(AtomicReaderContext).

Declaration

public override void SetTopValue<TValue>(TValue value) where TValue : class

Parameters

Type	Name	Description
TValue	value	The `T` value to use as the top value.

Type Parameters

Name	Description
TValue

Overrides

FieldComparer.SetTopValue<TValue>(TValue)

Exceptions

Type	Condition
ArgumentException	`value` does not derive from `T` and is not `null`.