[SOLR-12712] use JSON reach DSL format for aggregations in JSON.Facet

• Type: New Feature
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: Facet Module
• Assignee: Unassigned
• Reporter: Mikhail Khludnev
• Created: 28/Aug/18 22:37
• Updated: 08/Jun/19 14:59

Description

Context 

[Aggregations|https://lucene.apache.org/solr/guide/7_4/json-facet-api.html#aggregation-functions are nested into facets to handle enclosing buckets. They are supplied as a strings expression, which is handled by ValueSourceParser or so.

Problem 

Passing complex expression as a comma separated list of arguments are problematic, it leads to the verbose naming scheme or puzzling name overload convention with optional arguments. see SOLR-12711, SOLR-12325. For example, StreamingExpressions use name value syntax that's more powerful. 

Suggesition

Either introduce JSON syntax for subfacet aggregations, or if nested facets are able to aggregate enclosing buckets, introduce a expandable parsers (plugin point) for JSON.Facet.