The ClojureWerkz Blog

News and updates about ClojureWerkz projects

Welle 1.5.0 Is Released


Welle is an expressive Clojure client for Riak with batteries included.

1.5.0 is a minor release that is 100% backwards-compatible with 1.5.x and introduces several nice features:

  • Retriers for failing operations
  • Conflict resolvers
  • Easier to use update functions

This version has been tested against Riak 1.2.x and 1.3.x.

Changes between Welle 1.4.0 and 1.5.0


clojurewerkz.welle.kv/modify is a new function that combines clojurewerkz.welle.kv/fetch and clojurewerkz.welle.kv/store with a user-provided mutation functions. The mutation function should take a single Riak object as an immutable map and return a modified one.

In case of siblings, a resolver should be used.

clojurewerkz.welle.kv/modify will update modification timestamp of the object.

clojurewerkz.welle.kv/modify takes the same options as clojurewerkz.welle.kv/fetch and clojurewerkz.welle.kv/store

Conflcit Resolvers

clojurewerkz.welle.kv/fetch, and clojurewerkz.welle.kv/store now accept a new option: :resolver. Resolvers are basically pure functions that take a collection of siblings and return a collection of Riak object maps.

Resolvers can be created using clojurewerkz.welle.conversion/resolver-from which takes a function that accepts a collection of deserialized (unless fetch was told otherwise) values and applies any conflict resolution logic necessary.

clojurewerkz.welle.kv/fetch-one now also supports resolvers via the :resolver option. It will raise an exception if siblings are detected and no resolver is provided.


clojurewerkz.welle.kv/fetch, clojurewerkz.welle.kv/fetch-one, clojurewerkz.welle.kv/store, clojurewerkz.welle.kv/delete, and clojurewerkz.welle.kv/index-query now retry operations that fail due to a network issue or any other exception.

By default, the operations will be retrier 3 times. It is possible to provide a custom retrier using the :retrier option. Retriers can be created using clojurewerkz.welle.conversion/retrier-from which takes a function that accepts a callable (an operation that may need to be retried) and needs to invoke it, handling exceptions and applying any retrying logic needed.

clojurewerkz.welle.conversion/counting-retrier produces a retrier that will retry an operation given number of times. This is the kind of retrier Welle uses by default.

Skipping Deserialization for clojurewerkz.welle.kv/fetch

clojurewerkz.welle.kv/fetch supports a new boolean option :skip-deserialize that allows automatic deserialization to be skipped.

Contributed by Jonas Tehler.

Clojure 1.5 By Default

Welle now depends on org.clojure/clojure version 1.5.1. It is still compatible with Clojure 1.3+ and if your project.clj depends on a different version, it will be used, but 1.5 is the default now.

We encourage all users to upgrade to 1.5, it is a drop-in replacement for the majority of projects out there.

Change Log

We recommend all users to upgrade to 1.5.0 a try.

Welle change log is available on GitHub.

Welle is a ClojureWerkz Project

Welle is part of the group of libraries known as ClojureWerkz, together with

  • Langohr, a Clojure client for RabbitMQ that embraces the AMQP 0.9.1 model
  • Elastisch, a minimalistic Clojure client for ElasticSearch
  • Monger, a Clojure MongoDB client for a more civilized age
  • Neocons, a feature rich idiomatic Clojure client for the Neo4J REST API
  • Quartzite, a powerful scheduling library

and several others. If you like Welle, you may also like our other projects.

Let us know what you think on Twitter or on the Clojure mailing list.


ClojureWerkz accepts donations. If you feel like our projects save you time, consider donating. Thanks.

Michael on behalf of the ClojureWerkz Team