Using decision tree faceting

Imagine that in our store we have products divided into categories. In addition to this, we store information about the stock of the items. Now, we want to show our crew how many of the products in the categories are in stock and how many are missing. The first thing that comes to mind is to use the faceting mechanism and some additional calculation. But why bother, when Solr 4.0 and later can do that calculation for us with the use of so-called pivot faceting? This recipe will show you how to use it.

How to do it...

1. We start with defining the index structure that we can easily use. We do this by adding the following field definitions to the schema.xml file:

   <field name="id" type="string" indexed="true" stored="true" required="true" />
   <field name="name" type="text_general" indexed="true" stored="true" />
   <field name="category" type="string" indexed="true" stored="true" />
   <field name="stock" type="boolean" indexed="true" stored="true" /&gt...