Django AppData

Extendable field and related tools that enable Django apps to extend your reusable app.

Motivation

When working with reusable django apps we often found that we needed to add something extra to the model or form the app provided. Some apps try to solve this by providing a flexible model definition and a pluggable form (see django.contrib.comments for an exmple of this approach) but even then it leads to some duplication of efforts.

django-appdata app tries, through AppDataField, MultiForm and AppDataModelAdmin, to provide a standardised approach to extending existing apps.

Supported versions

Python: 3.9, 3.10, 3.11 Django: 3.2, 4.2

Upgrading to 0.4

If you are upgrading from a 0.3.x version, please note the following incompatible changes in 0.4

• Dropped Django < 3.2 and Python < 3.9 compatibility

Extending Models

When you have an extendable django app using the AppDataField:

from django.db import models
from app_data import AppDataField

class BlogPost(models.Model):
    text = models.TextField()
    app_data = AppDataField()

your code can register a namespace on any (or all) AppDataField and store it's own data there by registering a container (subclass of AppDataContainer). To define the data you use django's form framework:

from django.forms.models import ModelMultipleChoiceField
from app_data import app_registry, AppDataForm, AppDataContainer

from .models import Tag

class TaggingAppDataForm(AppDataForm):
    public_tags = ModelMultipleChoiceField(Tag.objects.all())
    admin_tags = ModelMultipleChoiceField(Tag.objects.all())

class TaggingAppDataContainer(AppDataContainer):
    form_class = TaggingAppDataForm

    def tag_string(self):
        print ', '.join(t.name for t in self.public_tags)

app_registry.register('tagging', TaggingAppDataContainer)

This should give you access to 'tagging' namespace in any defined AppDataField:

from blog_app.models import BlogPost

bp = BlogPost()
assert bp.app_data.tagging.tag_string() == ""

Additional Options

Note that if you don't need to add custom methods to your container you can just use a factory to create the subclass:

app_registry.register('tagging', AppDataContainer.from_form(TaggingAppDataForm))

Additionaly you can restrict the registration to a given model:

from blog_app.models import BlogPost

app_registry.register('tagging', TaggingAppDataContainer, BlogPost)

Extending Forms

django-appdata supplies a MultiForm class - a wrapper around django's ModelForm with optional added sub-forms that corresponds to namespaces registered in the model's AppDataField, typically the extendable app would create and use a MultiForm instead of a regular ModelForm:

from app_data.forms import multiform_factory
from .models import BlogPost

BlogPostMultiForm = multiform_factory(BlogPost)

And when using that app any project can add additional sub-forms to that MultiForm:

from blog_app.forms import BlogPostMultiForm

BlogPostMultiForm.add_form('tagging', {'fields': ['public_tags']})

This way when the reusable app's code can remain unchanged and we can inject additional form logic to its processing.

Additional Options

Any arguments and keyword arguments are passed without change to the ModelForm class the MultiForm is wrapping so even if you have custom args for your ModelForm everything will still work:

from django.forms.models import BaseModelForm

class ModelFormWithUser(ModelForm):
    def __init__(self, user, *args, **kwargs):
        self.user = user
        super(ModelFormWithUser, self).__init__(*args, **kwargs)

BlogPostMultiForm = multiform_factory(BlogPost, form=ModelFormWithUser)

And of course you are not limited to the use of a factory function:

from app_data import MultiForm

class MyMultiForm(MultiForm):
    ModelForm = BlogPostModelForm

MultiForms in Admin

If you wish to add your own code to the admin interface, just use AppDataModelAdmin:

from django.contrib import admin
from app_data.admin import AppDataModelAdmin
from blog_app.models import BlogPost

class BlogPostAdmin(AppDataModelAdmin):
    # due to the behavior of django admin validation we need to use
    # get_fieldsets instead of just fieldsets
    def get_fieldsets(self, request, obj=None):
         return [
             (None, {'fields': ['text', ]}),
             ('Tagging', {'fields': [('tagging.public_tags', 'tagging.admin_tags')]})
         ]
admin.site.register(BlogPost, BlogPostAdmin)

Additional Options

As with django's admin and forms you can supply your own MultiForm class by using the multiform attribute of AppDataModelAdmin.

Behind the scenes

django-appdata uses a TextField to store the data on the model using JSON and django's forms framework for (de)serialization and validation of the data.

When accessing the containers in the field we will try to locate the appropriate container in the registry. If none is found, plain data will be returned if present (dict). To assure everything working properly we recommend putting some sort of init code in place for your project that will make sure all the registration is done before any actual code is run. We are using a module called register in our apps and then a piece of code similar to admin's autodiscover to iterate through installed apps and load this module.

Build status

Master branch: