How do I connect to a MySQL database from Clojure?

问题

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

回答1:

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

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.
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
```
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
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

回答2:

This is a lein-friendly answer, with much guidance from this blog by Nurullah Akkaya:

add dependencies to your project.clj:

(defproject clojql "1.0.0-SNAPSHOT"
  :description "FIXME: write description"
  :dependencies [[org.clojure/clojure "1.2.1"]
                 [org.clojure/clojure-contrib "1.2.0"]   ;; for clojure.contrib.sql
                 [org.clojure/java.jdbc "0.0.6"]         ;; jdbc 
                 [mysql/mysql-connector-java "5.1.6"]])  ;; mysql driver

run lein deps from the command line to grab the dependencies

specify your connection information in a map:

user=> (use 'clojure.contrib.sql)
nil
user=> (def db {:classname "com.mysql.jdbc.Driver" 
                :subprotocol "mysql" 
                :subname "//localhost:3306/nmr" 
                :user "root"})

use with-connection and with-query-results macros (& others):

user=> (with-connection db (with-query-results rs ["select * from sometable"] (count rs)))
667

steps 3 & 4 can either be from the repl (lein repl to start it) or within normal source code

回答3:

As of 2016:

using Leiningen, add dependencies inside project.clj:

:dependencies [[org.clojure/clojure "1.8.0"]
               [org.clojure/java.jdbc "0.4.2"]
               [mysql/mysql-connector-java "5.1.38"]]

require database connector inside namespace definition:

(ns name.space
  (:require [clojure.java.jdbc :as j]))

define database connection:

(def db-map {:subprotocol "mysql"
             :subname "//localhost:3306/SCHEME"
             :user "DB_USER"
             :password "DB_USER_PASS"})

query the database:

(j/query db-map ["SELECT * FROM table"])

find more examples at http://clojure-doc.org/articles/ecosystem/java_jdbc/using_sql.html

回答4:

If you want some syntactic sugar, you can try Korma.

Docs

Github

(use 'korma.db)
(defdb db (postgres {:db "mydb"
                     :user "user"
                     :password "dbpass"}))

(use 'korma.core)
(defentity users)


(select users)
;; executes: SELECT * FROM users


(select users
  (where (or (= :usersname "chris")
             (= :email "chris@chris.com"))))
;; executes: SELECT * FROM users WHERE (users.usersname = 'chris' OR users.email = 'chris@chris.com')

来源：https://stackoverflow.com/questions/613929/how-do-i-connect-to-a-mysql-database-from-clojure

标签

mysql

clojure