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 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:

This is a Lucene.NET EXPERIMENTAL API, use at your own risk
Inheritance
System.Object
FieldComparer
FieldComparer<T>
FieldComparer.DocComparer
FieldComparer.NumericComparer<T>
FieldComparer.RelevanceComparer
FieldComparer.TermOrdValComparer
FieldComparer.TermValComparer
Inherited Members
Namespace: Lucene.Net.Search
Assembly: Lucene.Net.dll
Syntax
public abstract class FieldComparer<T> : FieldComparer
Type Parameters
Name Description
T

Methods

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Compare(Int32, Int32)

Compare hit at slot1 with hit at slot2.

Declaration
public abstract override int Compare(int slot1, int slot2)
Parameters
Type Name Description
System.Int32 slot1

first slot to compare

System.Int32 slot2

second slot to compare

Returns
Type Description
System.Int32

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
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CompareBottom(Int32)

Compare the bottom of the queue with this doc. This will only invoked after SetBottom(Int32) has been called. This should return the same result as Compare(Int32, Int32) 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 abstract override int CompareBottom(int doc)
Parameters
Type Name Description
System.Int32 doc

Doc that was hit

Returns
Type Description
System.Int32

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
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CompareTop(Int32)

Compare the top value with this doc. This will only invoked after SetTopValue(Object) has been called. This should return the same result as Compare(Int32, Int32) 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 abstract override int CompareTop(int doc)
Parameters
Type Name Description
System.Int32 doc

Doc that was hit

Returns
Type Description
System.Int32

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
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CompareValues(T, T)

Returns -1 if first is less than second. Default impl to assume the type implements and invoke ; be sure to override this method if your FieldComparer's type isn't a or if your values may sometimes be null

Declaration
public virtual int CompareValues(T first, T second)
Parameters
Type Name Description
T first
T second
Returns
Type Description
System.Int32
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CompareValues(Object, Object)

Returns -1 if first is less than second. Default impl to assume the type implements and invoke ; be sure to override this method if your FieldComparer's type isn't a or if your values may sometimes be null

Declaration
public override int CompareValues(object first, object second)
Parameters
Type Name Description
System.Object first
System.Object second
Returns
Type Description
System.Int32
Overrides
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Copy(Int32, Int32)

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 abstract override void Copy(int slot, int doc)
Parameters
Type Name Description
System.Int32 slot

Which slot to copy the hit to

System.Int32 doc

DocID relative to current reader

Overrides
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SetBottom(Int32)

Set the bottom slot, ie the "weakest" (sorted last) entry in the queue. When CompareBottom(Int32) is called, you should compare against this slot. This will always be called before CompareBottom(Int32).

Declaration
public abstract override void SetBottom(int slot)
Parameters
Type Name Description
System.Int32 slot

the currently weakest (sorted last) slot in the queue

Overrides
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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 abstract override 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
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SetTopValue(Object)

Record the top value, for future calls to CompareTop(Int32). This is only called for searches that use SearchAfter (deep paging), and is called before any calls to SetNextReader(AtomicReaderContext).

Declaration
public abstract override void SetTopValue(object value)
Parameters
Type Name Description
System.Object value
Overrides