I read that a simple way to implement hierarchical facet is to concatenate
strings with a separator. Something like "level1>level2>level3" with ">" as the
separator.
A problem with this approach is that the number of facet values will greatly
increase.
For example I have a facet "Location" with the hierarchy country>state>city.
Using the above approach every single city will lead to a separate facet value.
With tens of thousands of cities in the world the response from Solr will be
huge. And then on the client side I'd have to loop through all the facet values
and combine those with the same country into a single value.
Ideally Solr would be "aware" of the hierarchy structure and send back
responses accordingly. So at level 1 Solr will send back facet values based on
country (100 or so values). Level 2 the facet values will be based on the
states within the selected country (a few dozen values). Next level will be
cities within that state. and so on.
Is it possible to implement hierarchical facet this way using Solr?
