nomad
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simple sql migration tool to save you from going mad
.. -- mode: rst --
======= Nomad
Nomad is a simple migration application, which specifically takes into account properties of development with DVCS and is completely agnostic from ORM or whatever you are using to access your database. It uses simple SQL scripts to migrate and can run pre- and post-processing routines written in any language (Python, Ruby or whatever do you use for your application).
Tests status: |travis|, changelog <https://github.com/piranha/nomad/blob/master/CHANGELOG.rst>
_
.. |travis| image:: https://travis-ci.org/piranha/nomad.png :target: https://travis-ci.org/piranha/nomad
.. begin-writeup
Layout
Nomad's migration store is a directory with nomad.ini
and directories with
migrations inside. Each such directory must contain migration.ini
to be
recognized as a migration and this directory name is an unique identifier of a
migration.
Your directory tree thus will look like this::
migrations/ nomad.ini 2011-11-11-first-migration/ migration.ini up.sql 2011-11-12-second-migration/ migration.ini 1-pre.py 2-up.sql 3-post.py 2011-11-13-third-migration/ migration.ini 1-pre.py 2-up.sql 3-post.sql.j2
Nomad uses table called nomad
to track what was applied already. It's just a
list of applied migrations and dates when they were applied.
Interface
To start working, create nomad.ini
, and initialize your database (I assume
it already exists)::
$ nomad init
Then you can start creating your first migration::
$ nomad create 0-initial
Put your ALTERs and CREATEs in 0-initial/up.sql
and apply a migration::
$ nomad apply -a # or nomad apply 0-initial
Nomad should report which migrations it applied successfully, but you can check
status of that with nomad ls -a
(or nomad ls
to see only unapplied
migrations).
I guess it's time to create new migration::
$ nomad create 1-next -d 0-initial
-d 0-initial
means you want your 1-next
to depend on 0-initial
. This
means Nomad will never apply 1-next
without applying 0-initial
first. You usually want to depend on migrations which created tables you're
going to alter, or just to make it easier - on the latest available migration.
Usage
There are three types of migration files that nomad
supports:
-
Plain SQL files with the extension
.sql
. Just put SQL commands you need to execute in the migration folder and they will be executed. -
Executable files. All file extensions are supported as long as the file is executable. These files must contain everything necessary to migrate your data, including setting up a database connection.
nomad
will pass all of theConfiguration
_ variables as environmental variables, prefixed with their section. -
Template files with the extension
.j2
. These templates will be passed through the Jinja2 templating library. You must install thejinja2
library for this functionality. The entireConfiguration
_ is available to the template files as a single dictionary. These could be useful if you are distributing an application where the end user needs to control some aspects of the migrations (ie. additional database users and passwords, additonal database names, etc.).::
nomad.ini
[db] another_user = reader another_pass = pass
::
migrations/0001-initial/up.sql.j2
CREATE ROLE {{ db.another_user }}; ALTER ROLE {{ db.another_user }} WITH NOSUPERUSER LOGIN PASSWORD '{{ db.another_pass }}' VALID UNTIL 'infinity';
Files inside of each migration folder are executed in lexicographical order.
Configuration
Nomad reads database connection information from the [nomad]
section of the
nomad.ini
file.
::
[nomad] engine = sqla url = pgsql://user:password@host:port/db
Possible configuration options:
-
engine
(required) - SQL engine to use, possible options:-
sqla
- use SQLAlchemy as an adapter, supports everything SQLAlchemy supports -
dbapi
- use regular DB API, supportssqlite
,mysql
andpgsql
-
-
url
(required) - URL to database, takes multiple options, see format below -
path
- path to migrations (default: directory withnomad.ini
)
Each migration has its own migration.ini
file, which, by default, has a
single configuration option, nomad.dependencies
, defining which migration
(or migrations) this one depends.
You may add your own configuration variables to either the nomad.ini
or
migration.ini
files and they will be available in your jinja2 templates
as a single dictionary and your executable files as environmental
variables.
Note that ini-files are parsed with extended interpolation (use it like
${var}
or ${section.var}
).
A few predefined variables are provided to every migration:
-
confpath
- path tonomad.ini
-
confdir
- path to directory, containingnomad.ini
-
dir
- path to directory of migration
Example configuration:
+------------------+---------------------------+------------------------------+ | configration | executable | template | +==================+===========================+==============================+ | :: | :: | :: | | | | | | [nomad] | NOMAD_ENGINE = sqla | nomad.engine = sqla | | engine = sqla | NOMAD_URL = someurl | nomad.url = someurl | | url = someurl | | | | | FOO_BAR = zeta | foo.bar = zeta | | [foo] | | | | bar = zeta | NOMAD_CONFPATH = path | nomad.confpath = path | | | NOMAD_CONFDIR = dir1 | nomad.confdir = dir1 | | | NOMAD_DIR = dir2 | nomad.dir = dir2 | +------------------+---------------------------+------------------------------+
URL format
Nomad can read connection url to database in a few various ways. ``nomad.url``
configuration option is a space separated list of descriptions of how Nomad can
obtain database connection url.
The easiest one is simply an url (like in config example). The others are:
- ``file:<path-to-file>`` - a path to file containing connection url
- ``env:<var-name>`` - an environment variable (do not prefix with `$`)
- ``py:<python.mod>:<variable.name>`` - a Python path to a module,
containing a variable with connection url
- ``cmd:<cmd-to-execute>`` - command to execute to get connection url
- ``json:<path-to-file>:key.0.key`` - path to file with JSON and then path
to a connection url within JSON object
- ``yaml:<path-to-file>:key.0.key`` - path to file with YAML and then path
to a connection url within YAML object
- ``ini:<path-to-file>:<section.key>`` - path to INI file (parsed by
configparser with extended interpolation) and then path to a connection url
within this file
An example::
[nomad]
url =
ini:${confdir}/../settings.ini:db.url
json:${confdir}/../settings.json:db.url
sqlite:///${confdir}/../local.db
Notice that in all cases in the end you have to return URL to a database in
normal format, i.e. ``dbtype://user:pass@host:port/dbname?options``.
``options`` are supported only by pgsql right now, whatever you put there, nomad
will do ``set ...`` before every migration. Note that if you do not supply
anything there, nomad sets ``statement_timeout`` to 1000 ms and ``lock_timeout``
to 500 ms by default.
Main ideas
----------
- There are no downgrades - nobody ever tests them, and they are rarely
necessary. Just write an upgrade if you need to cancel something.
- You can write migration in whatever language you want, Nomad only helps you
track applied migrations and dependencies.
- ``.sql`` is treated differently and executed against database, configured in
``nomad.ini``.
- Only ``.sql``, ``.j2``, and executable files (sorry, Windows! - though I am eager to
hear ideas how to support it) are executed. You can put READMEs, pieces of
documentation, whatever you want alongside your migrations.
- Name matters - everything is executed in order. Order is determined by using
human sort (so that ``x-1.sql`` is earlier than ``x-10.sql``, you can always
check sorting with ``ls --sort=version``).
.. end-writeup