django-appdata 0.1.6

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.

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() == ""

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

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.

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)

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 bug in django's admin validation we need to use
    # declared_fieldsets instead of just fieldsets
    declared_fieldsets = [
        (None, {'fields': ['text', ]}),
        ('Tagging', {'fields': [('tagging.public_tags', 'tagging.admin_tags')]})
    ]
admin.site.register(BlogPost, BlogPostAdmin)

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: