Package org.apache.lucene.search
Class FieldComparator<T>
- java.lang.Object
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- org.apache.lucene.search.FieldComparator<T>
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- Direct Known Subclasses:
FieldComparator.DocComparator
,FieldComparator.RelevanceComparator
,FieldComparator.TermOrdValComparator
,FieldComparator.TermValComparator
,SimpleFieldComparator
public abstract class FieldComparator<T> extends Object
Expert: a FieldComparator compares hits so as to determine their sort order when collecting the top results withTopFieldCollector
. The concrete public FieldComparator classes here correspond to the SortField types.The document IDs passed to these methods must only move forwards, since they are using doc values iterators to retrieve sort values.
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. Segment transitions are handled by creating a dedicated per-segmentLeafFieldComparator
which also needs to interact with theFieldValueHitQueue
but can optimize based on the segment to collect.The following functions need to be implemented
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compare(int, int)
Compare a hit at 'slot a' with hit 'slot b'. -
setTopValue(T)
This method is called byTopFieldCollector
to notify the FieldComparator of the top most value, which is used by future calls toLeafFieldComparator.compareTop(int)
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getLeafComparator(org.apache.lucene.index.LeafReaderContext)
Invoked when the search is switching to the next segment. You may need to update internal state of the comparator, for example retrieving new values from DocValues. -
value(int)
Return the sort value stored in the specified slot. This is only called at the end of the search, in order to populateFieldDoc.fields
when returning the top results.
- See Also:
LeafFieldComparator
- WARNING: This API is experimental and might change in incompatible ways in the next release.
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Nested Class Summary
Nested Classes Modifier and Type Class Description static class
FieldComparator.DocComparator
Sorts by ascending docIDstatic class
FieldComparator.DoubleComparator
Parses field's values as double (usingLeafReader.getNumericDocValues(java.lang.String)
and sorts by ascending valuestatic class
FieldComparator.FloatComparator
Parses field's values as float (usingLeafReader.getNumericDocValues(String)
and sorts by ascending valuestatic class
FieldComparator.IntComparator
Parses field's values as int (usingLeafReader.getNumericDocValues(String)
and sorts by ascending valuestatic class
FieldComparator.LongComparator
Parses field's values as long (usingLeafReader.getNumericDocValues(String)
and sorts by ascending valuestatic class
FieldComparator.NumericComparator<T extends Number>
Base FieldComparator class for numeric typesstatic class
FieldComparator.RelevanceComparator
Sorts by descending relevance.static class
FieldComparator.TermOrdValComparator
Sorts by field's natural Term sort order, using ordinals.static class
FieldComparator.TermValComparator
Sorts by field's natural Term sort order.
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Constructor Summary
Constructors Constructor Description FieldComparator()
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Method Summary
All Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description abstract int
compare(int slot1, int slot2)
Compare hit at slot1 with hit at slot2.int
compareValues(T first, T second)
Returns a negative integer if first is less than second, 0 if they are equal and a positive integer otherwise.abstract LeafFieldComparator
getLeafComparator(LeafReaderContext context)
Get a per-segmentLeafFieldComparator
to collect the givenLeafReaderContext
.abstract void
setTopValue(T value)
Record the top value, for future calls toLeafFieldComparator.compareTop(int)
.abstract T
value(int slot)
Return the actual value in the slot.
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Method Detail
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compare
public abstract int compare(int slot1, int slot2)
Compare hit at slot1 with hit at slot2.- Parameters:
slot1
- first slot to compareslot2
- second slot to compare- Returns:
- any
N < 0
if slot2's value is sorted after slot1, anyN > 0
if the slot2's value is sorted before slot1 and0
if they are equal
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setTopValue
public abstract void setTopValue(T value)
Record the top value, for future calls toLeafFieldComparator.compareTop(int)
. This is only called for searches that use searchAfter (deep paging), and is called before any calls togetLeafComparator(LeafReaderContext)
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value
public abstract T value(int slot)
Return the actual value in the slot.- Parameters:
slot
- the value- Returns:
- value in this slot
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getLeafComparator
public abstract LeafFieldComparator getLeafComparator(LeafReaderContext context) throws IOException
Get a per-segmentLeafFieldComparator
to collect the givenLeafReaderContext
. All docIDs supplied to thisLeafFieldComparator
are relative to the current reader (you must add docBase if you need to map it to a top-level docID).- Parameters:
context
- current reader context- Returns:
- the comparator to use for this segment
- Throws:
IOException
- if there is a low-level IO error
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compareValues
public int compareValues(T first, T second)
Returns a negative integer if first is less than second, 0 if they are equal and a positive integer otherwise. Default impl to assume the type implements Comparable and invoke .compareTo; be sure to override this method if your FieldComparator's type isn't a Comparable or if your values may sometimes be null
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