Category: General Development

PostgreSQL, how about you don’t make migration more complex

I am currently work on building a new site, from an existing one.  A lot of the front-end work is done, now to a lot of the admin.

Today a really quite annoying “feature” of PostgreSQL raises its head and takes up 3 hours of my time.  A lot of the data from the old site PHP/MySQL has been migrated to the new one Django/PostgreSQL which all worked fine, the front end works and its all lovely.  To maintain the old database id’s we inserted them all into the new database, this in itself is not the problem.  The problem arose what starting to adding new rows, which are expected to go to the end.

INSERT INTO table (title) VALUES ('my_title');

Instead of actually insert into a new row, this started working from id 1, throwing up errors whenever the id already existed and sometimes started to delete items from the end of the database.

Just what the hell.  After plenty of research and testing, initially expecting it to be a problem with my code and the problem is found.

Adding the Primary Key manually DOES NOT update the auto-increment value, and here is the fix (change field names where necessary)

SELECT SETVAL('sequence_name', (SELECT MAX(id) FROM table_name) + 1);

If you are using Django  you can generate the SQL by running, it does not run the automatically but you can pipe the response directly into the psql tool.

python manage.py sqlsequencereset appname

Very simple but this does not follow the MySQL style I am used to, then again SQLite also does things differently which had me stumped at first.

Using the 960 Grid System

Originally, the tutorials mentioned here, were going to include the 960 grid system.  After some thought weighing up the benefits on convenience, performance, future updates etc, I have decided this will not be used for the main site.

I will still do tutorials on designing & prototyping using the grid system but that is as far as I will go.

So what’s wrong with the grid system?

As a developer who is trying to build a site that performs well, write tutorials from real experience and allow myself to easily apply updates in the future things have had to change.

  • The grid system has a lot of CSS I will not personally be using in this site.  Granted I COULD remove this, but I could also create what I need myself.
  • Future updates…well I intend to actually improve the site as time progresses.  The design will evolve as more content in introduced to the site, 960 may not even be wide enough, however, the problem comes when needing to adjust column widths.  Using CSS on its own, you adjust the width of the 2 columns and your down.  Using the grid system, you need to go through the HTML adjust class names.
  • Without using the grid system I am also able to create another tutorial for site layouts.  The grid system is fairly self-explanatory and will be covered on the prototyping stage.
  • Fluid or expanded columns.  By default the 960 grid system does not support fluid layouts, there is a branch for fluid and elastic layouts, but at this stage I am not entirely sure how or what I want to achieve with this.

Dansette