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https://github.com/piranha/nomad

simple sql migration tool to save you from going mad
https://github.com/piranha/nomad

migration python sql

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simple sql migration tool to save you from going mad

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README 

        
.. -*- 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: |ci|, `changelog `_



.. |ci| image:: https://github.com/piranha/nomad/actions/workflows/build.yml/badge.svg

   :target: https://github.com/piranha/nomad/actions



.. 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:



1.  Plain SQL files with the extension ``.sql``. Just put SQL commands you need

    to execute in the migration folder and they will be executed.

2.  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 the `Configuration`_ variables as environmental variables, prefixed

    with their section.

3.  Template files with the extension ``.j2``. These templates will be

    passed through the Jinja2 templating library. You must install the

    ``jinja2`` library for this functionality. The entire `Configuration`_ 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, supports ``sqlite``, ``mysql`` and ``pgsql``



- ``url`` (required) - URL to database, takes multiple options, see format below

- ``path`` - path to migrations (default: directory with ``nomad.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 to ``nomad.ini``

- ``confdir`` - path to directory, containing ``nomad.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:`` - a path to file containing connection url

- ``env:`` - an environment variable (do not prefix with `$`)

- ``py::`` - a Python path to a module,

  containing a variable with connection url

- ``cmd:`` - command to execute to get connection url

- ``json::key.0.key`` - path to file with JSON and then path

  to a connection url within JSON object

- ``yaml::key.0.key`` - path to file with YAML and then path

  to a connection url within YAML object

- ``ini::`` - 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