I'm not a Lucene Guru so hopefully you get a more definitive response.
I believe this means you want a way to specify ... "Nulls High" / "Nulls
Low" for your field (in this case you want Nulls High I believe).
I haven't seen support for that (but it might exist). Looking at
StringValComparator I'd say support for it doesn't exist - it looks like
null is always treated as low. My thinking is that you'll have to create a
FieldComparatorSource/FieldComparator :
SortField(String field, FieldComparatorSource comparator);
There are a bunch of implementations (static classes) in FieldComparator
(DoubleComparator, FloatComparator etc).
I believe you might need to create one of those. For example, I'm looking at
StringValComparator and I don't see a Null's High/ Nulls Low option in the
compare method.
Maybe that helps. Hopefully someone else can be more helpful. Would be nice
to have a Nulls High/Nulls Low support built in.
... source code of StringValComparator from lucene version 3
/** Sorts by field's natural String sort order. All
* comparisons are done using String.compareTo, which is
* slow for medium to large result sets but possibly
* very fast for very small results sets. */
public static final class StringValComparator extends FieldComparator {
private String[] values;
private String[] currentReaderValues;
private final String field;
private String bottom;
StringValComparator(int numHits, String field) {
values = new String[numHits];
this.field = field;
}
@Override
public int compare(int slot1, int slot2) {
final String val1 = values[slot1];
final String val2 = values[slot2];
if (val1 == null) {
if (val2 == null) {
return 0;
}
return -1;
} else if (val2 == null) {
return 1;
}
return val1.compareTo(val2);
}
@Override
public int compareBottom(int doc) {
final String val2 = currentReaderValues[doc];
if (bottom == null) {
if (val2 == null) {
return 0;
}
return -1;
} else if (val2 == null) {
return 1;
}
return bottom.compareTo(val2);
}
@Override
public void copy(int slot, int doc) {
values[slot] = currentReaderValues[doc];
}
@Override
public void setNextReader(IndexReader reader, int docBase) throws
IOException {
currentReaderValues = FieldCache.DEFAULT.getStrings(reader, field);
}
@Override
public void setBottom(final int bottom) {
this.bottom = values[bottom];
}
@Override
public Comparable<?> value(int slot) {
return values[slot];
}
}
On Wed, May 19, 2010 at 4:18 AM, comparis.ch - Roman Baeriswyl <
[email protected]> wrote:
> Hi All
>
> I've got a problem I'm trying to solve the whole day:
>
> Let's say I have an index with two fields, the first one is always filled
> and the second one only sometimes.
> Now I want to search something on the first field and want the results
> sorted by relevance, then by the first field, then by the second field.
> My problem now is that, if I have a lot of Entries with the same value in
> the first field and no value in the second field, these entries with no
> value on the 2nd field are coming first.
>
> Is there any way to increase the score on those documents which have a
> value on the second field? Or is there any way to skip those Documents which
> don't have the second field? I don't want to use a Filter, it should all be
> done with the Queries Objects if possible.
>
> I tried a lot of things with WildcardQuery or TermRangeQuery (with null
> values or empty strings) in Luke and directly in IndexSearcher, but I always
> get either no results or all results, even those which have no value in the
> second field.
>
> I found a lot of information where "-field2:[* TO *]" or similar stuff
> should work but it doesn't.
>
> Can anyone give me some hints?
>
> Thanks
> Roman
>
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