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Monarch

A Leiningen plugin to handle rails-style migrations.

Usage

Use this for user-level plugins:

Put [monarch "0.2.2"] into the :plugins vector of your :user profile, or if you are on Leiningen 1.x do lein plugin install monarch 0.2.2.

Use this for project-level plugins:

Put [monarch "0.2.2"] into the :plugins vector of your project.clj.

The default config will look for migration files in data/migrations, and will track which versions have been applied in the schema_versions table. You can override these defaults by adding a :migrations key pointing at a map in your project.clj like this:

:migrations {:table       "schema_versions"
             :location    "data/migrations"
             :config-lens :helloworld}
  • :location identifies where to look for migrations.
  • :table is the name of the table that tracks which migrations have been applied.
  • :config-lens is a path inside the :env key of ~/.lein/profiles.clj where monarch will look for the necessary configuration variables.

Caveats

This library has only been tested on Unix with Postgres. If you encounter any issues with your platform/database, please open an issue.

Setup

Monarch uses environ for environment configuration. It needs to know how to connect to your database, and does this by looking for a DATABASE_URL environment variable.

It is recommended that you export this variable as such (Unix):

export DATABASE_URL="postgresql://localhost:5432/helloworld"

This can get cumbersome for development, so you can also specify this in ~/.lein/profiles.clj.

{:user
    {:env
        {:helloworld {:database-url "postgresql://localhost:5432/helloworld"}}}}

You will also need to add the [lein-enviorn "0.5.0"] to the :plugins vector in project.clj.

If you are working with multiple projects with conflicting keys, then it's recommended that you scope DATABASE_URL underneath a project identifier. This identifier can be configured in project.clj, and is mentioned above. If you don't need to worry about this, then you can simply leave the var underneath :env. Monarch will check the project scoped key first. After that it will look for the exported environment variable, then a :database-url key in profiles.clj.

Once you've done that, run lein monarch setup to create the table that tracks the applied migrations. By default this is schema_versions, but can be overridden as mentioned above.

Migrations

Migrations are currently E.D.N. data, and take the form of a map with an :up and :down keys:

{:up [] :down []}

You can place an arbitrary sequence of statements in the supplied vector, and they will be executed in the order defined. All statements are applied in a transaction.

Example:

{:up ["CREATE TABLE users (
          id SERIAL PRIMARY KEY,
          email TEXT,
          password TEXT
       )"
      "CREATE TABLE posts (
          id SERIAL,
          user_id INTEGER REFERENCES users(id),
          title TEXT,
          body TEXT
      )"]
 :down ["DROP TABLE posts"
        "DROP TABLE users"]}

Quick Tutorial

  1. Create a new project with lein new hello-world

  2. cd into the project and add [monarch "0.2.2"] to the :plugins key in project.clj

  3. Run lein deps

  4. Startup Postgres and create a database named "helloworld".

  5. Export the following environment variable. Note that your connection information might be different:

    export DATABASE_URL="postgresql://localhost:5432/helloworld"

  6. Run lein monarch setup.

  7. Run lein monarch generate create_users

  8. Edit the resulting migration in data/migrations to look like the migration above.

  9. run lein monarch up

There is an example app too.

Available Commands

Examples

$ lein monarch setup           # Run necessary setup.
$ lein monarch generate <name> # generate a new migration file
$ lein monarch
$ lein monarch up              # apply all outstanding migrations
$ lein monarch rollback        # roll the database back one version

License

Copyright © 2014 G. Michael Cramm

Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.