Ferret

Highlighting Query Results

Query highlighting, like excerpting, is one of the newer features in Ferret, added in version 0.10. Highlighting takes a query and returns the data from a document field with all of the matches in the field highlighted. Excerpting, on the other hand, takes excerpts from the field, preferably with matching terms, and highlights the terms in those excerpts. Both Ferret::Search::Searcher and Ferret::Index::Index classes have a highlight method. In this section, we’ll look at Index#highlight because it allows us to pass string queries instead of having to build Query objects (see Table 4-3). Otherwise, both methods are essentially the same. To use the highlight method, you must supply a query and the document ID of the document you wish to highlight. A number of other parameters can be used to describe exactly how you want to highlight the field.

Table 4-3. Index#highlight parameters

Parameter	Description
:field	Defaults to @options[:default_field]. The highlighter only works on one field at a time, so you need to specify which field it is you want to highlight. If you want to highlight multiple fields, you'll need to call this method multiple times.
:excerpt_length	Defaults to 150 bytes. This parameter specifies the length of excerpt to show. The algorithm for extracting excerpts attempts to fit as many matched terms into each excerpt as possible. If you’d simply like the complete field back with all matches highlighted, set this parameter to :all.
:num_excerpts ...