Integrating Versioning

Let’s say we have an existing blog application. To make the blog app work with versioning, you would need to take the following steps:

1. Change the model structure.

2. Register the Post model for versioning

3. (optionally as needed) Implement a custom copy function

4. (optionally as needed) Additional/advanced configuration

Change the model structure

Assuming that our blog app has one db table:

This would have to change to a db structure like this:

Or in python code, models.py would need to change from:

# blog/models.py
from django.db import models
from django.contrib.sites.models import Site


class Post(models.Model):
    site = models.ForeignKey(Site, on_delete=models.CASCADE)
    title = models.CharField(max_length=100)
    text = models.TextField()

To:

# blog/models.py
from django.db import models
from django.contrib.sites.models import Site


class Post(models.Model):
    site = models.ForeignKey(Site, on_delete=models.CASCADE)


class PostContent(models.Model):
    post = models.ForeignKey(Post, on_delete=models.CASCADE)
    title = models.CharField(max_length=100)
    text = models.TextField()

Post becomes a grouper model and PostContent becomes a content model.

Keep in mind that it’s not necessary to name the content model PostContent, it’s just a naming convention. You could name the content model Post and have PostGrouper as the name of grouper model or come up with completely different naming.

Once the integration with versioning is complete, versioning will treat Post as the object being versioned and PostContent as a place to store data specific to each version. So every Post object will potentially have many PostContent objects referring to it via the post foreign key field. The states of the PostContent versions (whether they’re published, drafts etc.) are represented in a separate model called Version, which has what is effectively a one2one relationship with PostContent.

Deciding which fields should be in the content model and which in the grouper model depends on which data should be versioned and which should not. In this example we’re assuming that which site a blog post appears on cannot be changed, therefore we would not want to version it (it never changes so there’s nothing to version!). But if your project assumes that the site can be changed and those changes should be versioned, we would put that field in the PostContent model.

Register the model for versioning

Now we need to make versioning aware of these models. So we have to register them in the cms_config.py file. A very basic configuration would look like this:

# blog/cms_config.py
from cms.app_base import CMSAppConfig
from djangocms_versioning.datastructures import VersionableItem, default_copy
from .models import PostContent


 class BlogCMSConfig(CMSAppConfig):
    djangocms_versioning_enabled = True
    versioning = [
        VersionableItem(
            content_model=PostContent,
            grouper_field_name='post',
            copy_function=default_copy,
        ),
    ]

In this configuration we must specify the content model (PostContent), the name of the field that is a foreign key to the grouper model (post) and a copy function. For simple model structures, the default_copy function which we have used is sufficient, but in many cases you might need to write your own custom copy function (more on that below).

Once a model is registered for versioning its behaviour changes:

1. It’s default manager (Model.objects) only sees published versions of the model. See :term:content model.

2. It’s Model.objects.create method now will not only create the content model but also a corresponding Version model. Since the Version model requires a User object to track who created which version the correct way of creating a versioned content model is:

   Model.objects.with_user(request.user).create(...)
   

In certain situations, e.g., when implementing a copy function, this is not desirable. Use Model._original_manager.create(...) in such situations.

Note

If you want to allow using your models with and without versioning enabled we suggest to add dummy manager to your model that will swallow the with_user() syntax. This way you can always create objects with:

class ModelManager(models.Manager):
    def with_user(self, user):
        return self

class MyModel(models.Model):
    objects = ModelManager()

    ...

For more details on how cms_config.py integration works please check the documentation for django-cms>=4.0.

Accessing content model objects

Versioned content model objects have a customized objects manager which by default only creates querysets that return published versions of the content object. This will ensure that only published objects are visible to the public.

In some situations, namely when working in the admin, it is helpful to also have other content objects available, e.g. when linking to a not-yet-published object.

Versioned objects therefore also have an additional manager admin_manager which can access all objects. To get all draft blog posts, you can write PostContent.admin_manager.filter(versions__state=DRAFT). Since the admin_manager has access to non-public information it should only be used inside the Django admin (hence its name).

Implement a custom copy function

Whilst simple model structures should be fine using the default_copy function, you will most likely need to implement a custom copy function if your content model does any of the following:

• Contains any one2one or m2m fields.

• Contains a generic foreign key.

• Contains a foreign key that relates to an object that should be considered part of the version. For example if you’re versioning a poll object, you might consider the answers in the poll as part of a version. If so, you will need to copy the answer objects, not just the poll object. On the other hand if a poll has an fk to a category model, you probably wouldn’t consider category as part of the version. In this case the default copy function will take care of this.

• Other models have reverse relationships to your content model and should be considered part of the version

So let’s get back to our example and complicate the model structure a little. Let’s say our blog app supports the use of polls in posts and also our posts can be categorized. Now our blog/models.py now looks like this:

# blog/models.py
from django.db import models
from django.contrib.sites.models import Site


class Category(models.Model):
    name = models.CharField(max_length=100)


class Post(models.Model):
    site = models.ForeignKey(Site, on_delete=models.CASCADE)


class PostContent(models.Model):
    post = models.ForeignKey(Post, on_delete=models.CASCADE)
    title = models.CharField(max_length=100)
    text = models.TextField()
    category = models.ForeignKey(Category, on_delete=models.CASCADE)


class Poll(models.Model):
    post_content = models.ForeignKey(PostContent, on_delete=models.CASCADE)
    name = models.CharField(max_length=100)


class Answer(models.Model):
    poll = models.ForeignKey(Poll, on_delete=models.CASCADE)
    text = models.CharField(max_length=100)

If we were using the default_copy function on this model structure, versioning wouldn’t necessarily do what you expect. Let’s take a scenario like this:

1. A Post object has 2 versions - version #1 which is archived and version #2 which is published.

2. We revert to version #1 which creates a draft version #3.

3. The PostContent data in version #3 is a copy of what was in version #1 (the version we reverted to), but the Poll and Answer data is what was there at the time of version #2 (the latest version).

4. We edit both the PostContent, Poll and Answer data on version #3.

5. The PostContent data is now different in all three versions. However, the poll data is the same in all three versions. This means that the data edit we did on version #3 (a draft) to Poll and Answer objects is now being displayed on the published site (version #2 is published).

This is probably not how one would want things to work in this scenario, so to fix it, we need to implement a custom copy function like so:

# blog/cms_config.py
from cms.app_base import CMSAppConfig
from djangocms_versioning.datastructures import VersionableItem
from .models import PostContent, Poll, Answer


def custom_copy(original_content):
    content_fields = {
        field.name: getattr(original_content, field.name)
        for field in PostContent._meta.fields
        # don't copy pk because we're creating a new obj
        if PostContent._meta.pk.name != field.name
    }
    new_content = PostContent._original_manager.create(**content_fields)
    original_polls = Poll.objects.filter(post_content=original_content)
    for poll in original_polls:
        poll_fields = {
            field.name: getattr(poll, field.name)
            for field in Poll._meta.fields
            # don't copy pk because we're creating a new obj
            # don't copy post_content fk because we're assigning
            # the new PostContent object to it
            if field.name not in [Poll._meta.pk.name, 'post_content']
        }
        new_poll = Poll.objects.create(post_content=new_content, **poll_fields)
        for answer in poll.answer_set.all():
            answer_fields = {
                field.name: getattr(answer, field.name)
                for field in Answer._meta.fields
                # don't copy pk because we're creating a new obj
                # don't copy poll fk because we're assigning
                # the new Poll object to it
                if field.name not in [Answer._meta.pk.name, 'poll']
            }
            Answer.objects.create(poll=new_poll, **answer_fields)
    return new_content


 class BlogCMSConfig(CMSAppConfig):
    djangocms_versioning_enabled = True
    versioning = [
        VersionableItem(
            content_model=PostContent,
            grouper_field_name='post',
            copy_function=custom_copy,
        ),
    ]

As you can see from the example above the copy function takes one param (the content object of the version we’re copying) and returns the copied content object. We have customized it to create not just a new PostContent object (which default_copy would have done), but also new Poll and Answer objects.

Note

A custom copy method will need to use the content model’s PostContent._original_manager to create only a content model object and not also a Version object which the PostContent.objects manager would have done!

Notice that we have not created new Category objects in this example. This is because the default behaviour actually suits Category objects fine. If the name of a category changed, we would not want to revert the whole site to use the old name of the category when reverting a PostContent object.

Adding Versioning Entries to a Content Model Admin

Versioning provides a number of actions and fields through the ExtendedVersionAdminMixin, these function by extending the ModelAdmin list_display to add the fields:

• author

• modified date

• versioning state

• preview action

• edit action

• version list action

class PostContentAdmin(ExtendedVersionAdminMixin, admin.ModelAdmin):
    list_display = "title"

The ExtendedVersionAdminMixin also has functionality to alter fields from other apps. By adding the admin_field_modifiers to a given apps cms_config, in the form of a dictionary of {model_name: {field: method}}, the admin for the model, will alter the field, using the method provided.

# cms_config.py
def post_modifier(obj, field):
    return obj.get(field) + " extra field text!"

class PostCMSConfig(CMSAppConfig):
    # Other versioning configurations...
    admin_field_modifiers = [
        {PostContent: {"title": post_modifier}},
    ]

Given the code sample above, “This is how we add” would be displayed as “this is how we add extra field text!” in the changelist of PostAdmin.

Adding status indicators to a versioned content model

djangocms-versioning provides status indicators for django CMS’ content models, you may know them from the page tree in django-cms:

You can use these on your content model’s changelist view admin by adding the following fixin to the model’s Admin class:

import json
from djangocms_versioning.admin import StateIndicatorMixin


class MyContentModelAdmin(StateIndicatorMixin, admin.ModelAdmin):
    # Adds "indicator" to the list_items
     list_items = [..., "state_indicator", ...]

Note

For grouper models the mixin expects that the admin instances has properties defined for each extra grouping field, e.g., self.language if language is an extra grouping field. If you derive your admin class from GrouperModelAdmin, this behaviour is automatically observed.

Otherwise, this is typically set in the get_changelist_instance method, e.g., by getting the language from the request. The page tree, for example, keeps its extra grouping field (language) as a get parameter to avoid mixing language of the user interface and language that is changed.

def get_changelist_instance(self, request):
    """Set language property and remove language from changelist_filter_params"""
    if request.method == "GET":
        request.GET = request.GET.copy()
        for field in versionables.for_grouper(self.model).extra_grouping_fields:
            value = request.GET.pop(field, [None])[0]
            # Validation is recommended: Add clean_language etc. to your Admin class!
            if hasattr(self, f"clean_{field}"):
                value = getattr(self, f"clean_{field}")(value):
            setattr(self, field) = value
        # Grouping field-specific cache needs to be cleared when they are changed
        self._content_cache = {}
    instance = super().get_changelist_instance(request)
    # Remove grouping fields from filters
    if request.method == "GET":
        for field in versionables.for_grouper(self.model).extra_grouping_fields:
            if field in instance.params:
                del instance.params[field]
    return instance

Adding Status Indicators and Versioning Entries to a versioned content model

Both mixins can be easily combined. If you want both, state indicators and the additional author, modified date, preview action, and edit action, you can simpliy use the ExtendedIndicatorVersionAdminMixin:

class MyContentModelAdmin(ExtendedIndicatorVersionAdminMixin, admin.ModelAdmin):
    ...

The versioning state and version list action are replaced by the status indicator and its context menu, respectively.

Add additional actions by overwriting the self.get_list_actions() method and calling super().

Adding Versioning Entries to a Grouper Model Admin

Django CMS 4.1 and above provide the GrouperModelAdmin as to creat model admins for grouper models. To add version admin fields, use the ExtendedGrouperVersionAdminMixin:

class PostAdmin(ExtendedGrouperVersionAdminMixin, GrouperModelAdmin):
    list_display = ["title", "get_author", "get_modified_date", "get_versioning_state"]

ExtendedGrouperVersionAdminMixin also observes the admin_field_modifiers.

Note

Compared to the ExtendedVersionAdminMixin, the ExtendedGrouperVersionAdminMixin does not automatically add the new fields to the list_display.

The difference has compatibility reasons.

To also add state indicators, just add the StateIndicatorMixin:

class PostAdmin(ExtendedGrouperVersionAdminMixin, StateIndicatorMixin, GrouperModelAdmin):
    list_display = ["title", "get_author", "get_modified_date", "state_indicator"]

Summary admin options

Overview on versioning admin options: Grouper models

Versioning state	Grouper Model Admin
Text, no interaction	class GrouperAdmin( ExtendedGrouperVersionAdminMixin, GrouperModelAdmin ) list_display = ...
Indicators, drop down menu	class GrouperAdmin( ExtendedGrouperVersionAdminMixin, StateIndicatorMixin, GrouperModelAdmin ) list_display = ...

Overview on versioning admin options: Content models

Versioning state	Content Model Admin
Text, no interaction	class ContentAdmin( ExtendedVersionAdminMixin, admin.ModelAdmin )
Indicators, drop down menu	class ContentAdmin( ExtendedIndicatorVersionAdminMixin, admin.ModelAdmin, )

Additional/advanced configuration

The above should be enough configuration for most cases, but versioning has a lot more configuration options. See the advanced_configuration page for details.