Simplest ever migrations for clojure project.

config.clj

(ns config)

(def db-spec (or (System/getenv "DATABASE_URL")
                 "postgres://pin:password@localhost:5432/pin")) 

migration.clj

(ns migration
  (:require [clojure.java.jdbc :as sql]
            [config]))

(defn- db-do
       "Do something with db connection"
       [fn]
       (sql/db-do-commands config/db-spec fn))

(defn init!
      "Inits migration engine - creates migration table" 
      []
      (try
        (db-do (sql/create-table-ddl :migrations [[:name "VARCHAR(80) PRIMARY KEY"]]))
        (catch Exception _)))

(defn migrated?
      "Is migration already performed?"
      [name]
      (-> (sql/query config/db-spec ["select count(*) from migrations where name = ?" name])
          first
          :count
          pos?))

(defn migration-applied! 
      [name]
      (sql/insert! config/db-spec 
                   :migrations
                   [:name]
                   [name]))

(defn add-table! 
      "Simple adds table to database. If migration already applied - will return false and no makes changes to database"
      [migration-name table spec]
      (cond
            (migrated? migration-name) false
            :else (do
                    (db-do (sql/create-table-ddl table spec))
                    (migration-applied! migration-name))))

(defn sql-request!
      "Plain sql-request migration. Applies once(checks by name of migration)"
      [migration-name query]
      (cond
            (migrated? migration-name) false
            :else (do
                      (migration-applied! migration-name)
                      (sql/query config/db-spec query))))

migrations.clj

(ns project.migrations
  (:require [migration :as m]))

(declare create-users create-chains create-posts)

(defn migrate
      "Perform all migrations" 
      []
      (m/init!)
      (create-users)
      (create-chains)
      (create-posts))

;; --------------- Here goes migrations -----------------------------------
(defn- create-users
      []
      (m/add-table! "Create table users" :users [[:uuid "UUID PRIMARY KEY"]
                                                 [:name :varchar]
                                                 [:hash :varchar]
                                                 [:local :boolean]]))
(defn- create-chains
       []
       (m/add-table! "Create table chains" :chains [[:uuid "UUID PRIMARY KEY"]
                                                    [:name :varchar]]))

(defn- create-posts
       []
       (m/add-table! "Create table posts" :posts [[:uuid "UUID PRIMARY KEY"]
                                                  [:creator_uuid :uuid]
                                                  [:chain_uuid :uuid]
                                                  [:title :varchar]
                                                  [:body :text]
                                                  [:branch :uuid]]))