Greg Miller created LUCENE-9945:
-----------------------------------
Summary: Extend DrillSideways to support exposing FacetCollectors
directly
Key: LUCENE-9945
URL: https://issues.apache.org/jira/browse/LUCENE-9945
Project: Lucene - Core
Issue Type: Improvement
Components: modules/facet
Affects Versions: main (9.0)
Reporter: Greg Miller
The {{DrillSideways}} logic currently encapsulates, 1) the creation of multiple
{{FacetsCollector}} instances, and 2) the processing of those
{{FacetsCollector}}s into a single {{Facets}} instance. While I suspect this
works well for most common cases, and is simple to understand, it's difficult
to extend to more advanced cases.
I propose extending {{DrillSideways}} to support exposing the underlying
{{FacetsCollector}} instances if the user needs them, in addition to
maintaining the current functionality for all of the more common cases.
Specifically, I'd like to add both the "drill down" {{FacetsCollector}} and map
of dim -> {{FacetsCollector}} for "drill sideways" to the
{{DrillSidewaysResult}} and {{ConcurrentDrillSidewaysResult}} classes. While
it's true that a user can extend {{DrillSideways}} and override
{{buildFacetsResult}} to keep track of these, it seems reasonable to provide
this in {{DrillSideways}} itself so users don't need to sub-class for only this
purpose.
Here are two use-cases illustrating the desire for this:
# For certain cases, instead of actually creating a {{Facets}} instance from
the {{FacetsCollector}}, I'd like to intersect the {{FacetsCollector}} matching
docs with a {{TermEnum}} to do determine whether-or-not at least one match
exists. This is useful for a "facet" that can only take on the values
"true"/"false", and I want to make sure at least one hit has the value "true".
# In another case, I only care about some aggregate statistics for a given
facet field. For example, I want to find the min and max values. For this, I
want to intersect some doc value field with a {{FacetsCollector}} and only
track the min/max values I observe while iterating.
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