Java typesafe queries

When looking on the official Java driver API, we can see an effort to make an API as fluent as possible:

collection.find(and(gte("stars", 2),
                    lt("stars", 5),
                    eq("categories", "Bakery")));

Yet, there are many issues:

  • All fields are Strings without auto completion.
  • No type safety on operators (Is stars a number?! Is categories a collection (?!) of Strings or …?!).
  • Do we really like using gte for >= ?! I mean, is it easy to read and understand this expression?
  • And finally, when the schema changes, we are back to 80’ with find-replace…

There is a simple and effective solution to those issues — FluentMongo, which adds the missing ingredient to the API — type safety and Java integration. It lets you use normal Java to write filters, projections, updates, sorts and indexes. For example:

collection.find(builder.filter(r -> r.getStars() >= 2 &&
                                    r.getStars() < 5 &&

As an author of this OSS library, I would be happy to learn about the value and usability of this solution.