Ferret

Building Queries

Even if you are using the QueryParser to build all your queries, you’ll gain a better understanding of how searching works in Ferret by building each of the queries by hand. We’ll also include the Ferret Query Language (FQL) syntax for each different type of query as we go. As you read, you’ll find some queries that you can’t build even using the QueryParser, so it will be useful to learn about them as well.

Before we get started, we should mention that each Query has a boost field. Because you will usually be combining queries with a BooleanQuery, it can be useful to give some of those queries a higher weighting than the other clauses in the BooleanQuery. All Query objects also implement hash and eql?, so they can be used in a HashTable to cache query results.

Tokenizing Query Terms

When building queries by hand, it is important to consider how the data is tokenized when you add terms to the queries. For example, “red-face” could be stored in the index as a single term or it might be stored as two terms, “red” and “face”. You need to make sure that you build queries with this in mind. If “red-face” is tokenized as a single term, you can use a TermQuery. If it’s tokenized as two separate terms, you’ll need to use a PhraseQuery.

It becomes more complicated when you use an analyzer that stems and removes stop words. If you try to use a TermQuery to search for the word “the” when your analyzer removed stop words, you’ll likely get no results. If you used a stemmer, you ...