django-vcexport 0.5.1

a flexible library for exporting serialized django model instances to a version-controlled repository automatically or manually

How it works

There is an application-level API and a model-level API.

Use the model-level API to define export behavior per model class, with automatic exports on save.

Use the application-level API to define export behavior in views (for example) and explicitly trigger content export from your own code.

The model-level API

The design is inspired by Django’s ModelAdmin and ModelForm aspect-oriented pattern. The core behaviors are defined in the vcexport.models.Exporter class, which is analogous to ModelAdmin. Like ModelAdmin and ModelForm, you will subclass the default base to customize the behavior on a per-model basis.

1. For automatic versioning of models, register them with vcexport:

   import vcexport
   vcexport.register(MyModel)
   

   This will connect a post_save signal.

2. You can customize the export behavior on a per-model basis by subclassing vcexport.models.Exporter and telling vcexport to register your model with the custom Exporter:

   class MyExporter(vcexport.models.Exporter):
     ...
   vcexport.register(MyModel, exporter=MyExporter)
   

3. By default, models are serialized to django’s XML format, because it works well with diff and is generic.

4. You can customize the serialization per model by passing a custom template path as a class attribute:

   class MyExporter(Exporter):
       repository_template = 'fleem/document_format.txt'
   

   The template will be rendered with two context variables; object which is the model instance that was saved, and a boolean created:

   {% if created %}New object!{% endif %}
   {{object.title}}
   {{object.related_field.pk}}
     ****
   Color: {{object.color}}
   {{object.description}}
   

   This allows alternate use cases to be supported:

   • You want to version a model wholesale
   • You have a model which has one or two document-like text fields, and you want to version those fields only – just don’t write out any other fields in the serialization template.

5. By default the document dumps of your model instances will be saved in repository paths that look like /app_name/ModelClassName/instance_pk.

   You can customize the path:

   class MyExporter(Exporter):
       def repository_path(self):
           return '/my_custom/path_for/this_model/' + self.object.color
   

   Note that if you do this, you may end up with multiple model instances that save to the same file path in the repository. This is a feature.

6. The default committing user is undefined. At present you cannot customize this.

   The default commit message is uninteresting: “Object {{instance.pk}} (from ‘{{app_name}}.{{model_name}}’) saved by django-vcexport.”

   You can customize the commit message with a model method that takes a boolean created, and returns a string:

   class MyExporter(Exporter):
       def repository_commit_message(self, created):
           if created:
               return "User %s committed a new %s" % (
                 self.object.user.username, self.object.color)
           return "User %s committed %s" % (self.object.user.username,
                                            self.object.color)
   

The application-level API

You can also export the content explicitly, for example in your model’s save() method, in view code, etc, with the vcexport.export_to_repository function:

def my_view(request):
    ...
    object = MyModel.objects.get(...)
    object.morx = request.POST['new_morx']
    object.save()

    import vcexport
    vcexport.export_to_repository(object)

The default template, commit message, etc are the same as with the model API. You can customize them in your own code and pass them to export_to_repository:

def my_view(request):
    ...
    object, created = MyModel.objects.get_or_create(...)
    object.morx = request.POST['new_morx']
    object.save()

    import vcexport
    vcexport.export_to_repository(
               object, created=created,
               repository_template='/fleem/morx.html',
               message="Changed the morx",
               repository_path='/fleem/objects/%s' % object.pk)

The export_to_repository function will return the Revision of the commit, or None if there were no changes to commit.

Configuration

You must provide one piece of configuration in your settings.py file:

• VCEXPORT_CHECKOUT_DIR: the absolute path to a local checkout of the repository that you want to store your data in

You will have to initialize your repository and checkout on your own.

To use with Subversion, you must have pysvn installed.

Originally developed at Columbia University’s Center for New Media Teaching & Learning <http://ccnmtl.columbia.edu>

New in this version

Brown-bag release; made export_to_repository function available as public API (vcexport.export_to_repository)

History

0.5 (06-12-09)

Split apart distinct APIs for model-level behavior and application-level usage.

0.4 (24-11-09)

Initial release. This package was previously called svndjango. It was redesigned from the ground up and renamed django-vcexport to describe more accurately what it does.