BlockJoin facets allow you to aggregate children facet counts by their parents.
It is a common requirement that if a parent document has several children documents, all of them need to increment facet value count only once. This functionality is provided by BlockJoinDocSetFacetComponent, and BlockJoinFacetComponent just an alias for compatibility.
This functionality is considered deprecated and will be removed at 9.0.
Users are encouraged to use `uniqueBlock(\_root_)` aggregation under a `terms` facet in the <<json-faceting-domain-changes.adoc#block-join-domain-changes,JSON Facet API>>.
If this component is used, it must be explicitly enabled for a request handler in solrconfig.xml, in the same way as any other search component.
This example shows how you could add this search components to solrconfig.xml and define it in request handler: