Schemamigration

As progress is made through any project, there comes a time when the creators realize that the models that they had in mind for the final product aren't sufficient to complete the task. At this point, the models must be revised in order to accomplish the goals of the project.

Unfortunately, if the project that is being built involves a database, this adapting of the model can be a difficult process. In our case, we decided to add in a schedule to every light, room, and house. The Django framework is under strict instructions to create tables, but not to update them. Then, when you choose to add something, the Django website will throw an error because it doesn't understand why there is an extra thing added into its design. If the story ends there, that means that every time we adapt our model we will have to re-create all of the test data that we have generated, adding in the schedule information as we build it new.

Fortunately, the story doesn't end there. The good folks at Aeracode have developed South, a data migration tool for Django projects. South takes care of the difficult task of adapting the database for you. All that one needs to do is set up an initial state of the database with the South tool and then when a change has been made, create and apply a data migration. For our purposes, it worked very smoothly and the tutorial was easy to follow. 

After installing South, there were just four simple commands to run:

./manage.py syncdb

./manage.py convert_to_south myapp

./manage.py schemamigration myapp --auto

./manage.py migrate myapp

The only minor hiccup in the migration was that the database did not know what value to fill in for the schedule for each of the lights. Since the lights are allowed to not be on a schedule, a quick null=true fixed this problem and our app was fully functional again.