[SOLR-1672] RFE: facet reverse sort count

• Type: Improvement
• Status: Closed
• Priority: Minor
• Resolution: Workaround
• Affects Version/s: 1.4
• Component/s: search

Environment

Java, Solrj, http

• Assignee: Unassigned
• Reporter: Peter Sturge
• Created: 18/Dec/09 09:54
• Updated: 28/Jun/17 21:45
• Resolved: 28/Jun/17 21:45

Description

As suggested by Chris Hosstetter, I have added an optional Comparator to the BoundedTreeSet<Long> in the UnInvertedField class.
This optional comparator is used when a new (and also optional) field facet parameter called 'facet.sortorder' is set to the string 'dsc'
(e.g. &f.<facetname>.facet.sortorder=dsc for per field, or &facet.sortorder=dsc for all facets).
Note that this parameter has no effect if facet.method=enum.
Any value other than 'dsc' (including no value) reverts the BoundedTreeSet to its default behaviour.

This change affects 2 source files:
> UnInvertedField.java
[line 438] The getCounts() method signature is modified to add the 'facetSortOrder' parameter value to the end of the argument list.

DIFF UnInvertedField.java:

• public NamedList getCounts(SolrIndexSearcher searcher, DocSet baseDocs, int offset, int limit, Integer mincount, boolean missing, String sort, String prefix) throws IOException {

+ public NamedList getCounts(SolrIndexSearcher searcher, DocSet baseDocs, int offset, int limit, Integer mincount, boolean missing, String sort, String prefix, String facetSortOrder) throws IOException

{ [line 556] The getCounts() method is modified to create an overridden BoundedTreeSet<Long>(int, Comparator) if the 'facetSortOrder' parameter equals 'dsc'. DIFF UnInvertedField.java: - final BoundedTreeSet<Long> queue = new BoundedTreeSet<Long>(maxsize); + final BoundedTreeSet<Long> queue = (sort.equals("count") || sort.equals("true")) ? (facetSortOrder.equals("dsc") ? new BoundedTreeSet<Long>(maxsize, new Comparator() { @Override public int compare(Object o1, Object o2) { if (o1 == null || o2 == null) return 0; int result = ((Long) o1).compareTo((Long) o2); return (result != 0 ? result > 0 ? -1 : 1 : 0); //lowest number first sort }}

) : new BoundedTreeSet<Long>(maxsize)) : null;

> SimpleFacets.java
[line 221] A getFieldParam(field, "facet.sortorder", "asc"); is added to retrieve the new parameter, if present. 'asc' used as a default value.
DIFF SimpleFacets.java:

+ String facetSortOrder = params.getFieldParam(field, "facet.sortorder", "asc");

[line 253] The call to uif.getCounts() in the getTermCounts() method is modified to pass the 'facetSortOrder' value string.
DIFF SimpleFacets.java:

• counts = uif.getCounts(searcher, base, offset, limit, mincount,missing,sort,prefix);
  + counts = uif.getCounts(searcher, base, offset, limit, mincount,missing,sort,prefix, facetSortOrder);

Implementation Notes:
I have noted in testing that I was not able to retrieve any '0' counts as I had expected.
I believe this could be because there appear to be some optimizations in SimpleFacets/count caching such that zero counts are not iterated (at least not by default)
as a performance enhancement.
I could be wrong about this, and zero counts may appear under some other as yet untested circumstances. Perhaps an expert familiar with this part of the code can clarify.
In fact, this is not such a bad thing (at least for my requirements), as a whole bunch of zero counts is not necessarily useful (for my requirements, starting at '1' is just right).

There may, however, be instances where someone will want zero counts - e.g. searching for zero product stock counts (e.g. 'what have we run out of'). I was envisioning the facet.mincount field
being the preferred place to set where the 'lowest value' begins (e.g. 0 or 1 or possibly higher), but because of the caching/optimization, the behaviour is somewhat different than expected.