Diagrams.net Django Tutorial

To use pyMDG we need to build:

  • A UML model

  • A generation recipe

Data Modelling

pyMDG has a specific UML nomenclature. This needs to be added into diagrams.net by selecting:

File -> Open Library From -> URL and enter:


This will result in the pyMDG library being added to the sidebar:


UML packages are set up as Frames in the library. This mimics the hierarchy found in full modelling tools like Sparx. Add 3 nested frames to the canvas and rename each:

  • Top level is the name of our business domain/data platform

  • 2nd level is the model container (test container can be added later)

  • 3rd level is a data domain/app


We can then start modelling classes. Each class must have an attribute with {id} except where the {id} is in a parent class.

Drag 2 ‘Class Basic’ objects into the TestDomain package. Rename classes and set the {id} attribute of each class. Drag on an Association and link the classes:


There are 5 templates for classes:

  • Basic: Vanilla class with attributes

  • Abstract: The <<auto>> attribute stereotype is optional.

  • Stereotyped: Shows auditable (data platform will track changes) and notifiable (changes will cause events to be sent to the message broker)

  • Routable: When events are sent to message broker then routing keys will include attributes with <<routable>> stereotype.

pyMDG supports 4 relation types:

  • Association: Forms relations between classes:

    • One to One

    • One to Many

    • Many to One

    • Many to Many

  • Generalization: Defines a parent/child inheritance

  • Composition: Similar to association but can be used to control generated features. For example, when generating an OpenAPI schema, objects which are part of a composition may not get thier own endpoint.

  • Aggregation: Like composition aggregations affect the features of our output. For example, an OpenAPI generation can use aggregations to specifiy when the endpoint is a sub-endpoint I.e. /customer/12/customer_address/1/

Export the diagram by File -> Export As -> XML and unselect Compressed


The recipe tells pyMDG about your model and what files to output. This tutorial uses the sample templates and config which you can find in the sample_recipe folder from the project on gitgub: https://github.com/Semprini/pyMDG

recipe - Django

A complete django app with django rest api can be created from the model.

cd into a new project folder (I called mine django-tut):

django-tut> virtualenv venv
django-tut> pip install pymdg

Copy the following from the github project pyMDG/sample_recipe/drawio folder:

  • config-drawio-django.yaml

The dir structure now looks like:


Edit config-drawio-django.yaml and update the following:

  • root_package: QuickStart (matches the top level package)

  • model_package: model (matches the middle package)

  • source: the path to your saved model file

  • templates_folder: ‘’

  • dest_root: ./build

We can now build the project:

> django-tut> mdg-tool generate .\config-drawio-django.yaml
Config file loaded: .\config-drawio-django.yaml
Base Model Package: model
Generating model output for package /QuickStart/
Generating model output for package /QuickStart/TestDomain/
Generating test case output

And then run the generated django app:

> cd build/QuickStart/
> pip install -r .\requirements.txt
> python manage.py makemigrations TestDomain    <- matches the inner package
Migrations for 'TestDomain':
 - Create model AnotherClass
 - Create model MyCoolClass

> python manage.py migrate
> python manage.py createsuperuser
> python manage.py runserver

You can now browse to and