The document discusses the need for dynamic models in Django, which allow adaptation of models at runtime based on user interactions, contrasting with the static nature of traditional Django models. It outlines the challenges developers face with static models and presents solutions like the Entity-Attribute-Value (EAV) model and runtime schema updates to enhance flexibility. Furthermore, the document highlights the importance of integrating dynamic models with standard Django tools for improved user and developer experience.

1. Dynamic Models
in Django
Juergen Schackmann
j.schackmann@reliatec.de

2. © Juergen Schackmann 2013 2/28
Me
▸ Python & Django since 4 years
▸ reliatec.de since 3 months
▸ Django Web Applications
▸ Focus: EDC systems for clinical studies & Telemonitoring

3. © Juergen Schackmann 2013 3/28
Objective
▸ Why do do we care about Django Dynamic Models?
▸ Why do we have to talk about them?
▸ What should we do about them?

4. Static vs Dynamic Models

5. © Juergen Schackmann 2013 5/28
Models in a Django project
Phase1:
Code Development
Models and model
attributes are defined by
implementing those with
Python code
Phase 2:
Deployment
Underlying database tables
and columns are created by
running “syncdb” command
Phase 3:
Runtime
Models / DB Tables are
populated with content as
part of the user
interactions

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Problem?
There is no way to adapt the Django Models at runtime based on
user interactions
▸ Django Models are defined and implemented during
development phase
▸ Django Models are expected to be static after deployment
▸ Django DB Backends only fully support SQL databases, i.e. a
schema is required
▸ DB specific solutions limit adoption rate of any reusable App

7. Use Cases for Dynamic
Models

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Custom Content Types for a CMS*
* system: dotCms (Java); source: http://dotcms.com/

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Customized Products for an Ecommerce Shop*
* system: Magento (PHP); source: averybrandandprint.co.uk

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Clinical Research Forms*
* system: OpenClinica (Java); source: openclinica.com

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Problem? Which Problem?
▸ Models / Content Types are domain or site specific
▸ Neither realistic nor efficient to implement all thinkable content
types into a software product
▸ Configuration by subject-matter experts is better, than code
customization by developers
▸ Dynamic Models reduce the number of deployment cycles

12. Evaluation of
Patterns & Apps

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As a User, I ...
▸ want to maintain my dynamic models easily without
understanding any Django Model details
▸ want extend existing (static) models without thinking about
static and dynamic parts
▸ do not want to think about performance, when creating my
custom fields
▸ I want to be able to query/search for certain information
seamlessly over static and dynamic models

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As a developer, I ...
▸ want my dynamic models to be integrated with Django Standard
Tools (admin, migrations, reversion) out of the box
▸ want to apply the same API that I use for the static models
▸ do not want to use or be limited to specific databases, but use
the standard Django backends
▸ want to have a customizable front-end for my users to manage
the dynamic models

15. © Juergen Schackmann 2013 15/28
Evaluation Criteria
▸ Performance
▸ “Querybility”
▸ Django Standard Tools Integration (Admin, Cache, ...)
▸ Supported Backend
▸ Complexity/ Maintainability

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Entity Attribute Value (EAV)
Transform your table columns into table rows
Attribute 1 Attribute 2 Attribute n
Table
Attribute
Name
Attribute
Value
Attribute
TableTable has1 n

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EAV Django Apps
▸ bitbucket.org/neithere/eav-django/
▸ github.com/mvpdev/django-eav

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Serialized Dictionary
Transform your table columns into pickeld or jsoned dictionaries
Attribute 1 Attribute 2 Attribute n
Table
Dictionary
String
Attributes
{“attribute1”:”a”, “attribute2”: 5, “attribute3”:[1,2] }

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Serialized Dictionary Django Apps
Fields
▸ bitbucket.org/schinckel/django-jsonfield/
▸ github.com/bradjasper/django-jsonfield
▸ github.com/derek-schaefer/django-json-field
▸ github.com/shrubberysoft/django-picklefield
App
▸ github.com/dobarkod/django-dynamic-model

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Runtime Schema Updates
Update Django models and database schema at runtime using
▸ syncdb functionality
▸ South functionality
▸ eventually: Andrew Godwin's “Schema Migrations for Django”

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Runtime Schema Update Django Apps
Update Django models and database schema at runtime using
▸ Syncdb
▸ bitbucket.org/mhall119/dynamo/overview
▸ South
▸ github.com/willhardy/dynamic-models
▸ github.com/willhardy/django-dymo
▸ bitbucket.org/schacki/django-dynamo
▸ github.com/charettes/django-mutant
▸ Schema Migrations
▸ github.com/charettes/django-mutant

22. © Juergen Schackmann 2013 22/28
Database specific solutions
Hstore
▸ github.com/jordanm/django-hstore
▸ postgresql.org/docs/9.0/static/hstore.html
No SQL
▸ github.com/django-nonrel
▸ github.com/pydanny/django-mongonaut

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Summary
EAV Serialization Schema Updates
Performance   
Querybility   
Django Standard
Tools
 / 
Supported
Backend
  
Complexity/
Maintainability
  

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Schema Update most powerful, but ...
▸ Name clashes between developer models and dynamic models
(especially with schema migrations)
▸ Multiple Users updating the same model (possibly even
conflicting)
▸ Orphan database elements
▸ Dynamic Model loading at startup
▸ How to find/inject dynamic models into views and templates

25. Components of a
Dynamic Model App

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Must have components of a Dynamic Model
Application
▸ Meta Model Front End to let users maintain their meta models
▸ Meta Model Representation to store the meta model information
▸ Meta Model Analyzer to detect changes that require some further
actions (for schema, admin or model)
▸ Schema Sync Manager to update and sync the database schema
▸ Admin Sync Manager to update and sync the Django admin
▸ Model/Cache Sync Manager to update and sync the Django models
and model cache

27. © Juergen Schackmann 2013 27/28
More resources on dynamic models
▸ code.djangoproject.com/wiki/DynamicModels
▸ djangopackages.com/grids/g/forms/
▸ stackoverflow.com/questions/7933596/django-dynamic-model-
fields/7934577

28. Thank you very much!
Questions please?