Github user laimis commented on a diff in the pull request:
https://github.com/apache/lucenenet/pull/64#discussion_r23741168
--- Diff: src/Lucene.Net.Expressions/ExpressionRescorer.cs ---
@@ -0,0 +1,119 @@
+using System;
+using System.Collections.Generic;
+using Lucene.Net.Index;
+using Lucene.Net.Search;
+
+namespace Lucene.Net.Expressions
+{
+ /// <summary>
+ /// A
+ /// <see
cref="Lucene.Net.Search.Rescorer">Lucene.Net.Search.Rescorer</see>
+ /// that uses an expression to re-score
+ /// first pass hits. Functionally this is the same as
+ /// <see
cref="Lucene.Net.Search.SortRescorer">Lucene.Net.Search.SortRescorer
+ /// </see>
+ /// (if you build the
+ /// <see cref="Lucene.Net.Search.Sort">Lucene.Net.Search.Sort</see>
+ /// using
+ /// <see cref="Expression.GetSortField(Bindings,
bool)">Expression.GetSortField(Bindings, bool)
+ /// </see>
+ /// ), except for the explain method
+ /// which gives more detail by showing the value of each
+ /// variable.
+ /// </summary>
+ /// <lucene.experimental></lucene.experimental>
+ internal class ExpressionRescorer : SortRescorer
+ {
+ private readonly Expression expression;
+
+ private readonly Bindings bindings;
+
+ /// <summary>
+ /// Uses the provided
+ /// <see
cref="Lucene.Net.Queries.Function.ValueSource">Lucene.Net.Queries.Function.ValueSource
+ /// </see>
+ /// to assign second
+ /// pass scores.
+ /// </summary>
+ public ExpressionRescorer(Expression expression, Bindings
bindings) : base(new Sort
+ (expression.GetSortField(bindings, true)))
+ {
+ this.expression = expression;
+ this.bindings = bindings;
+ }
+
+ private class FakeScorer : Scorer
+ {
+ internal float score;
+
+ internal int doc = -1;
+
+ internal int freq = 1;
+
+ public FakeScorer() : base(null)
+ {
+ }
+
+ public override int Advance(int target)
+ {
+ throw new NotSupportedException("FakeScorer
doesn't support advance(int)");
+ }
+
+ public override int DocID()
+ {
+ return doc;
+ }
+
+ public override int Freq()
+ {
+ return freq;
+ }
+
+ public override int NextDoc()
+ {
+ throw new NotSupportedException("FakeScorer
doesn't support nextDoc()");
+ }
+
+ public override float Score()
+ {
+ return score;
+ }
+
+ public override long Cost()
+ {
+ return 1;
+ }
+
+ public override Weight Weight
+ {
+ get { throw new NotSupportedException(); }
+ }
+
+ public override ICollection<Scorer.ChildScorer> Children
+ {
+ get { throw new NotSupportedException(); }
+ }
+ }
+
+ /// <exception cref="System.IO.IOException"></exception>
+ public override Explanation Explain(IndexSearcher searcher,
Explanation firstPassExplanation
+ , int docID)
+ {
+ Explanation result = base.Explain(searcher,
firstPassExplanation, docID);
+ IList<AtomicReaderContext> leaves =
searcher.IndexReader.Leaves;
+ int subReader = ReaderUtil.SubIndex(docID, leaves);
+ AtomicReaderContext readerContext = leaves[subReader];
+ int docIDInSegment = docID - readerContext.DocBase;
+ var context = new Dictionary<string, object>();
+ var fakeScorer = new FakeScorer {score =
firstPassExplanation.Value, doc = docIDInSegment};
+ context["scorer"] = fakeScorer;
--- End diff --
indentation
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