by Juergen Schackmann
Django has been built on the assumption to have upfront static data models; i.e. the developer implements them completely before deployment. However, there are numerous real-world uses cases that require to have dynamic models that can be created and amended by users or some kind of user actions. Examples could be: customizable products for a shop, unique content types to represent web site content in a CMS or online surveys that are created on the fly.
There are various conceptual options to solve this problem. The most prominent ones are: a) Entity Attribute Value Models, b) Pickeld Fields and Pickeld Models, c) Database DDL operations at run-time Most of which have been discussed intensively and the Django community has developed numerous apps. I will compare the various approaches and apps in terms of usability, speed, features, sweet spots and preferred use cases. This will support any future evaluation for a specific project. But it will hopefully also trigger a fruitful community discussion on the importance of this feature for Django in comparison with other applications and frameworks like Zope/Plone, Magento etc.
How to do it¶
Entity attribute values
- Table columns become rows in another table’s rows
- Performance issues
Serialized Dictionary Django apps
- Dangerous because of use of Pickle
- Problematic because of lack of searchability (this is mitigated via tools like PostgreSQL hstore or MongoDB)
Runtime schema updates
Allow updates of the database schema by non-technical user action
- This sounds kind of of risky
Dynamic models problematic since it can interfere of how the database is designed.
Complexity is another issue. How do you keep the database from going nuts from user action?
Database integrity is a major issue.
Column updates is a really nasty issue. For example, the database has to lock the for minutes or hours.