aino-mutations

==============
aino-mutations
==============

aino-mutations is a tool to call mutation scripts at a certain revision
of a mercurial repository. Mutation scripts are typically scripts that perform
database refactoring of some sort. aino-convert is not intelligent:

- Does not offer introspection

- Mutation scripts are intended to use raw sql for schema migration
  which means you will be locked to a particular database engine, that of
  your own choice of course.


Why?
----
aino-mutations solves the problem of running a mutation in the correct
environment. Often when you do mutations you want to perform some logic
to insert or remove data. To perform this logic we need the environment
in which the mutation was written for. aino-convert automatically updates
a mercurial repository to the revision where the mutation was added and
executes the mutation script.


Requirements
------------

- Django with Multi DB support, v1.2+, or trunk until released.

- Mercurial, only tested with v1.5

- Django project managed by a mercurial repository


Installation
------------

1. Add ``mutations`` to your pythonpath

2. Add ``mutations`` to ``INSTALLED_APPS``


Configuration
-------------
Mutation scripts are by default looked for in a ``mutations`` subdirectory of
your mercurial repository root, you can change this by setting ``MUTATIONS_ROOT``
in your settings file. Note that ``MUTATIONS_ROOT`` should be a relative
directory path to your repository root.


Usage
-----
aino-mutations seperates mutations for different databases and therefore
you need to specify what database you are affecting with your mutation.
To add a mutation:

1. Add the python file (mutation) to ``MUTATIONS_ROOT/alias/``
   where ``alias`` is the alias used in your settings file
   (the default is called ``default``).

2. Add the file to the repository: ``hg add path/to/mutation``

3. Commit: ``hg ci -m"my first mutation"``

4. Now run the mutation: ``python manage.py mutate``


Mutations
---------
Mutations are just normal python files that do whatever you like.
For convenience there are some local variables passed to the mutation scripts:

- ``cursor``: a cursor instance for the current database

- ``commit_unless_managed`` is just a shortcut for
  ``django.db.transaction.commit_unless_managed``

- ``dry``: this will be True if ``mutate`` is run with the ``--dry`` option
  which can be usefull for displaying some info to the user.


FAQ
---

- *I created a mutation that was wrong, what do I do?*
- All you need to do is to remove it from the repository:
  ``hg rm path/to/mutation; hg ci -m"no more bad code"``


- *I want to try a mutation before commiting, how can i do that?*
- run: ``python manage.py runmutation path/to/mutation``


- *I have my django project in a deployment environment, can I still use
  aino-mutations?*
- The best way to solve this since aino-mutations may update project
  files to a certain revision while performing the mutations it is best to
  clone the repository to another location while accessing the same databases.