The ad hoc c* clj talk

The Driver

• Most clojure drivers for c* are wrapping Java drivers
• I recommend using one that wraps the DataStax Java Driver
• Good options are Cassaforte and Alia
• http://clojurecassandra.info/articles/getting_started.html
• I'll be walking through Cassaforte
• Helpful sometimes to reference the java driver https://github.com/datastax/java-driver

Connecting

What they show

(ns cassaforte.docs.examples
  (:require [clojurewerkz.cassaforte.client :as cc]))

;; Will connect to localhost
(cc/connect ["127.0.0.1"])

Connecting

(def cconnection (atom nil))
(def current-keyspace (atom nil)) 

(defn rebuild-connection []
  (let [{:keys [seed-list cassandra-user cassandra-pass]} (conf/get-cassandra-conf)]
    (reset! cconnection
            (apply cc/connect
                   (if cassandra-user
                     [seed-list {:credentials 
                                  {:username cassandra-user :password cassandra-pass}}]
                     [seed-list])))
    (reset! current-keyspace nil)))

(defn get-connection
  "Gets existing connection or creates a new one."
  [& [optional-keyspace & _]]
  (when-not @cconnection
    (locking cconnection
      (when-not @cconnection
        (rebuild-connection))))
  (when optional-keyspace
    (when (not= @current-keyspace optional-keyspace)
      (cql/use-keyspace @cconnection :my_data)))
  @cconnection)

What to do with state?  This works but it's ugly

Connecting

Way better ways?

• Manage lifecyle with something like componet https://github.com/stuartsierra/component
• Compose functions rather than relying on global state
• Dodge locks with mechanisms like core.async
• ~DO NOT~ just swap! an atom, resource leaks/etc 

Inserting

• Clojure DSL for CQL
• https://github.com/mpenet/hayt
• Both Cassaforte and Alia use this 

(:require '[clojurewerkz.cassaforte.client :as cc]
(:require '[clojurewerkz.cassaforte.cql    :as cql])

(def conn (cc/connect ["127.0.0.1"])

(cql/insert conn "test_data" {:data_id (int 42) :data_item "The Ultimate Answer"}))

Selecting

(cql/insert conn "test_data" {:data_id (int 42) :data_item "The Ultimate Answer"}))

(use '[clojurewerkz.cassaforte.query])

(cql/select conn "test_data" (where [[= :data_id (int 42)]]))

More Fun Stuff

• Use clj to launch ccm for repl/integration testing 
• https://github.com/SMX-LTD/ccm-clj
• A better demo than I have can be found here 
• https://github.com/nickmbailey/clojure-cassandra-demo
• Learn more about Cassandra at Datastax Academy for free 
• https://academy.datastax.com/