MIGRATE ALL THE THINGS!

A Leiningen plugin for the Migratus library.

A general migration framework, with an implementation for database migrations.

Designed to be compatible with a git based work flow where multiple topic branches may exist simultaneously, and be merged into a master branch in unpredictable order.

This is accomplished two ways:

1. Migration ids are not assumed to be incremented integers. It is recommended that they be timestamps (e.g. ‘20111202091200’).
2. Migrations are considered for completion independently.

In contrast, using a single global version for a store and incremented integers for migration versions, it is possible for a higher numbered migration to get merged to master and deployed before a lower numbered migration, in which case the lower numbered migration would never get run, unless it is renumbered.

Migratus does not use a single global version for a store. It considers each migration independently, and runs all uncompleted migrations in sorted order.

• Add Migratus as a dependency and the plugin:

  :dependencies [[migratus "0.9.9"]]
  :plugins [[migratus-lein "0.5.1"]]
      

• Add the following key and value to your project.clj:

  :migratus {:store :database
             :migration-dir "migrations"
             :db {:classname "com.mysql.jdbc.Driver"
                  :subprotocol "mysql"
                  :subname "//localhost/migratus"
                  :user "root"
                  :password ""}}
      

• Add the following code to “src/migrations/20111206154000-create-foo-table.up.sql”

  CREATE TABLE IF NOT EXISTS foo(id BIGINT);
      

• Run `lein migratus migrate`

Migratus is configured via a configuration map that you pass in as its first parameter. The :store key describes the type of store against which migrations should be run. All other keys/values in the configuration map are store specific.

To run migrations against a database use a :store of :database, and specify the database connection configuration in the :db key of the configuration map. This connection information is passed directly to clojure.java.jdbc. For example:

{:store :database
 :migration-dir "migrations"
 :db {:classname "com.mysql.jdbc.Driver"
      :subprotocol "mysql"
      :subname "//localhost/migratus"
      :user "root"
      :password ""}}

or:

{:store :database
 :migration-dir "migrations"
 :db ~(get (System/getenv) "DATABASE_URL")}

When using the second option, it’s also possible to put the config in profiles.clj, e.g:

{:provided {:env {:database-url "jdbc:h2:./my_app_dev.db"}}}

The second method is preferred as it doesn’t hardcode database connection values in files that are checked into the repository.

The :migration-dir key specifies the directory on the classpath in which to find SQL migration files. Each file should be named with the following pattern “[id]-[name]-[direction].sql” where id is a unique integer id for the migration, name is some human readable description of the migration, and direction is either ‘up’ or ‘down’.

If Migratus is trying to run either the up or down migration and it does not exist, then an Exception will be thrown.

If you would like to run multiple statements in your migration, then separate them with ‘–;;’. For example:

CREATE TABLE IF NOT EXISTS quux(id bigint, name varchar(255));
--;;
CREATE INDEX quux_name on quux(name);

This is necessary because JDBC does not have a method that allows you to send multiple SQL commands for execution. Migratus will split your commands, and send the each to the database inside of a transaction.

See test/migrations in this repository for an example of how database migrations work.

Migratus can be used programmatically by calling one of the following functions:

The ‘create’ command will generate the migration files with the supplied name. The files will be placed in the migrations directory. Each file will be prefixed with the current timestamp and the up migration file will be postfixed with ‘.up.sql`, while the down migration file will be postfixed with ‘.down.sql’, e.g:

lein migratus create add-users-table

will generate the following files:

20160303102023-add-users-table.down.sql
20160303102023-add-users-table.up.sql

See the docstrings of each function for more details.

Migratus can also be used from leiningen if you add it (and a database driver) as a dev dependency.

:dev-dependencies [[migratus "0.9.9"]
                   [postgresql/postgresql "9.1-901.jdbc4"]]

And add a configuration :migratus key to your project.clj.

:migratus {:store :database
           :migration-dir "migrations"
           :db "postgres://localhost/mydb"}

Copyright © 2012 Paul Stadig

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Licensed under the Apache License, Version 2.0.