Negated searches don't work properly with Combined Indexes

[Kathy Lussier]

We've seen issues with negated searches where records are retrieved even though they contain a search term thats should be excluded from the search. As an example, the search:

title:christmas subject:-christmas

will retrieve records with the word 'christmas' in the subject.

I've finally narrowed this down to the way Combined searches handle negated searches. By default, Evergreen enables the Combined flag for the subject class. You can replicate this issue on the Concerto dataset by running the following search:

subject:hogwarts -magic

This search will retrieve record 210, which does have the word 'magic' in one of the subject headings. In my testing, I've found it will retrieve a record containing the excluded term if at least one row in metabib.subject_field_entry for the retrieved record does not contain the search term.

If you remove the Combined flag for subject class searches on a Concerto dataset, the hogwarts search will work as expected.

[Kathy Lussier (klussier)]

A short-term fix for this bug would be to remove the combined flag as a default for the subject class, so that negated searches work properly for Evergreen catalogs.

However, we do want to see the underlying issue fixed so that more sites could move to combined indexes, allowing records to be retrieved when the keywords are located in different metabib rows for that record.