Hi folks,
I have a question on PerFieldSimilarityWrapper. It seems that it is
not possible to get per-field behavior on queryNorm() and coord()...
The documentation for PerFieldAnalyzerWrapper (lucene 4.0) says:
Subclasses should implement get(String) to return an appropriate
Similarity (for example, using field-specific parameter values) for
the field.
This leads the user to believe that *only* get() needs to be
overridden. However, I've found that I must override queryNorm() as
well, otherwise Similarity.queryNorm() will be called (because
PerFieldAnalyzerWrapper extends Similarity), not the user-supplied
version.
The test cases in lucene seem always to override queryNorm() and
(coord() too), but I don't see tests for the per-field behavior of
these. Indeed, there seems to be no way to get the field name from
these methods. And that's the problem. I'd like to have per-field
behavior for queryNorm() and coord().
Below is some code to illustrate the issue:
class MyPerFieldSimilarity1 extends PerFieldSimilarityWrapper {
@Override
public Similarity get(String name) {
return new DefaultSimilarity();
}
}
class MyPerFieldSimilarity2 extends PerFieldSimilarityWrapper {
@Override
public Similarity get(String name) {
return new DefaultSimilarity();
}
@Override
public float queryNorm(float valueForNormalization) {
// Notice that I don't have access to the read field name here...
return get("dummy").queryNorm(valueForNormalization);
}
}
public class PerFieldSimilarityWrapperTest {
private float runTest(Similarity similarity) throws IOException {
IndexWriterConfig config = new
IndexWriterConfig(Version.LUCENE_40, new
WhitespaceAnalyzer(Version.LUCENE_40));
config.setSimilarity(similarity);
Directory dir = new RAMDirectory();
IndexWriter writer = new IndexWriter(dir, config);
Document doc = new Document();
String fieldName = "some_field";
doc.add(new TextField(fieldName, "some text", Store.YES));
writer.addDocument(doc);
writer.commit();
IndexReader reader = DirectoryReader.open(dir);
IndexSearcher searcher = new IndexSearcher(reader);
searcher.setSimilarity(similarity);
TermQuery query = new TermQuery(new Term(fieldName, "text"));
TopDocs topDocs = searcher.search(query, 1);
float score = topDocs.scoreDocs[0].score;
return score;
}
public static void main(String[] args) throws IOException {
PerFieldSimilarityWrapperTest that = new
PerFieldSimilarityWrapperTest();
System.out.println(that.runTest(new DefaultSimilarity()));
System.out.println(that.runTest(new MyPerFieldSimilarity1()));
System.out.println(that.runTest(new MyPerFieldSimilarity2()));
}
}
Running this produces:
0.19178301
0.058849156
0.19178301
Am I overlooking something here or is this a bug?
Thanks,
- Joel
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