kirillk77/alia

Cassandra CQL3 Clojure client - datastax/java-driver wrapper

alia

Coan-Teen, the female death spirit who walks without feet.

Cassandra CQL3 client for Clojure wrapping datastax/java-driver.

What's in the box?

• Built on an extremely solid base, datastax/java-driver, based on the new CQL native protocol
• Simple API with a minimal learning curve
• Great performance
• Provides a versatile CQL3+ DSL, Hayt
• Support for Raw queries, Prepared Statements or Hayt queries
• Can do both Synchronous and Asynchronous query execution, using Lamina or clojure/core.async interface for async.
• Support for all of datastax/java-driver advanced options: jmx, auth, SSL, compression, consistency, custom executors, custom routing and more
• Support and sugar for query tracing, metrics, retry policies, load balancing policies, reconnection policies and UUIDs generation
• Extensible Clojure data types support & clojure.core/ex-data integration
• Lazy and potentialy chunked sequences over queries
• Controled rows streaming via core.async channels
• First class support for custom data types

Installation

The binary protocol server is not started with the default configuration file coming with Cassandra 1.2+ In the cassandra.yaml file, you need to set:

start_native_transport: true

Then add this to your dependencies:

If you are running Cassandra 2.0+:

[cc.qbits/alia "2.2.2"]

If you are running Cassandra 1.2:

[cc.qbits/alia "1.10.2"]

Please check the Changelog if you are upgrading.

Documentation

codox generated documentation.

Quickstart

Simple query execution using alia+hayt would look like this:

(execute session (select :users
                         (where {:name :foo})
                         (columns :bar "baz")))

But first things first: here is an example of a complete session using raw queries.

(require '[qbits.alia :as alia])

(def cluster (alia/cluster {:contact-points ["localhost"]}))

Sessions are separate so that you can interact with multiple keyspaces from the same cluster definition.

(def session (alia/connect cluster))

(alia/execute session "CREATE KEYSPACE alia
                       WITH replication = {'class': 'SimpleStrategy', 'replication_factor' : 3};")

   (alia/execute session "USE alia;")
   (alia/execute session "CREATE TABLE users (user_name varchar,
                                              first_name varchar,
                                              last_name varchar,
                                              auuid uuid,
                                              birth_year bigint,
                                              created timestamp,
                                              valid boolean,
                                              emails set<text>,
                                              tags list<bigint>,
                                              amap map<varchar, bigint>,
                                              PRIMARY KEY (user_name));")
  (alia/execute session "INSERT INTO users
                         (user_name, first_name, last_name, emails, birth_year, amap, tags, auuid,valid)
                         VALUES('frodo', 'Frodo', 'Baggins',
                         {'[email protected]', '[email protected]'}, 1,
                         {'foo': 1, 'bar': 2}, [4, 5, 6],
                         1f84b56b-5481-4ee4-8236-8a3831ee5892, true);")

  (def prepared-statement (alia/prepare session "select * from users where user_name=?;"))

  (alia/execute session prepared-statement {:values ["frodo"]})

  >> ({:created nil,
       :last_name "Baggins",
       :emails #{"[email protected]" "[email protected]"},
       :tags [4 5 6],
       :first_name "Frodo",
       :amap {"foo" 1, "bar" 2},
       :auuid #uuid "1f84b56b-5481-4ee4-8236-8a3831ee5892",
       :valid true,
       :birth_year 1,
       :user_name "frodo"})

Asynchronous interfaces:

There are currently 2 ways to use the asynchronous methods of the underlying driver, using a Lamina based api or the newly released clojure/core.async

Async using the Lamina based api

Using execute-async which is used the same way as execute, the return value is a result-channel from Lamina (you can think of it as an equivalent of a clojure.core/promise).

(def result (alia/execute-async session "select * from users;"))

To get the result once and wait for its realization we can dereference it, a blocking operation.

@result

Or we can use success/error handlers (it still returns a result-channel just like before).

(alia/execute-async session "select * from users;"
                    {:success (fn [rows] (do-something-with-result rows))
                     :error (fn [err] (print "fail!"))})

Async using clojure/core.async

alia/execute-chan has the same signature as the other execute functions and as the name implies returns a clojure/core.async channel that will contain a list of rows at some point or an exception instance.

Once you run it you have a couple of options to pull data from it.

• using clojure.core.async/take! which takes the channel as first argument and a callback as second:

(take! (execute-chan session "select * from users;")
       (fn [rows-or-exception]
         (do-something rows)))

• using clojure.core.async/<!! to block and pull the rows/exception from the channel.

(def rows-or-exception (<!! (execute-chan session "select * from users;")))

• using clojure.core.async/go block, and potentially using clojure.core.async/alt!.

(go
 (loop [;;the list of queries remaining
        queries [(alia/execute-chan session (select :foo))
                 (alia/execute-chan session (select :bar))
                 (alia/execute-chan session (select :baz))]
        ;; where we'll store our results
        query-results '()]
   ;; If we are done with our queries return them, it's the exit clause
   (if (empty? queries)
     query-results
     ;; else wait for one query to complete (first completed first served)
     (let [[result channel] (alts! queries)]
       (println "Received result: "  result " from channel: " channel)
       (recur
        ;; we remove the channel that just completed from our
        ;; pending queries collection
        (remove #{channel} queries)

        ;; and finally we add the result of this query to our
        ;; bag of results
        (conj query-results result))))))

And it can do a lot more! Head to the codox generated documentation.

Hayt (Query DSL)

There is a nicer way to write your queries using Hayt, this should be familiar if you know Korma or ClojureQL. One of the major difference is that Hayt doesn't use macros and just generates maps, so if you need to compose clauses or queries together you can just use the clojure.core functions that work on maps.

Some examples:

(use 'qbits.hayt)

(select :foo (where {:bar 2}))

;; this generates a map
>> {:select :foo :where {:bar 2}}

(update :foo
         (set-columns {:bar 1
                       :baz (inc-by 2)}
         (where [[= :foo :bar]
                 [> :moo 3]
                 [> :meh 4]
                 [:in :baz  [5 6 7]]]))


;; Composability using normal map manipulation functions

(def base (select :foo (where {:foo 1})))

(merge base
       (columns :bar :baz)
       (where {:bar 2})
       (order-by [:bar :asc])
       (using :ttl 10000))

;; To compile the queries just use ->raw or ->prepared

(->raw (select :foo))
> "SELECT * FROM foo;"

(->prepared (select :foo (where {:bar 1})))
> ["SELECT * FROM foo WHERE bar=?;" [1]]

Alia supports hayt query direct execution, if you pass a non-compiled query to execute or execute-async, it will be compiled and cached on a LU cache with a threshold of 100 (the cache function is user settable), so to be used carefully. The same is true with prepare.

Ex:

(execute session (select :users (where {:name :foo})))

It covers everything that is possible with CQL3 (functions, handling of collection types and their operations, ddl, prepared statements, etc). If you want to know more about it head to its codox documentation or Hayt's tests.

Mailing list

Alia has a mailing list hosted on google groups. Do not hesitate to ask your questions there.

License

Copyright © 2013-2014 Max Penet

Distributed under the Eclipse Public License, the same as Clojure.