How do I connect to a MySQL database from Clojure?

Question

Assumption: you already have both Clojure and MySQL running on your machine.
How do you make them talk?

Answer 1

Assumption: you already have both Clojure and MySQL running on your machine.

1. checkout and build clojure-contrib:

   git clone git://github.com/richhickey/clojure-contrib.git
   cd clojure-contrib
   build
   

   Put the resulting clojure-contrib.jar on your CLASSPATH.

2. Download MySQL Connector/J and put the mysql-connector-java-5.1.7-bin.jar on your CLASSPATH

   You might have to run your JVM with these arguments:

   -Djdbc.drivers=com.mysql.jdbc.Driver
   

3. Determine the connection URL of your MySQL database

   For example, if you are running MySQL under MAMP then the URL that you would use in JDBC will look something like:

   conn = DriverManager.getConnection
           ("jdbc:mysql://localhost:8889/db_name?user=root&password=root")
   

   The url is broken down into these components:

   • protocol: jdbc:
   • subprotocol: mysql
   • db-host: localhost
   • db-port: 8889
   • username
   • password

4. Make this clojure script, modify the database connection parameters to match your URL, save as test.clj, compile and run.

   (use 'clojure.contrib.sql)               ;;' satisfy prettify
   
   
     (let [db-host "localhost"
           db-port 8889
           db-name "db_name"]
       (def db {:classname "com.mysql.jdbc.Driver"
              :subprotocol "mysql"
              :subname (str "//" db-host ":" db-port "/" db-name)
              :user "root"
              :password "root"})
       (with-connection db
         (with-query-results rs ["select * from languages"]
           (dorun (map #(println (:language :iso_code %)) rs)))))
   
   
       ; rs will be a sequence of maps,
       ; one for each record in the result set.
   
   
   

   NB This code was adapted from similar code written by Mark Volkmann to access a Postgres database from Clojure