Django Logical Delete

This is a small and simple app that I threw together to get some reuse out of something I do in nearly every project and every model I create. It's too easy for good data to get deleted and it be unrecoverable. It's also too easy to fix this by overriding the model's delete() method and just flagging records as deleted and then leveraging Django's Managers to override default behavior so that logically deleted items are not returned in querysets.

There are two exceptions however, that I have found useful to this rule.

1. In the admin I like to see everything with an indicator of whether or not it has been deleted, with the ability to filter down to just active records, (or deleted for that matter).
2. I still think it is a valid request when an item is fetched for by it's primary key value, that the object should return, even if it is marked as deleted.

Using django-logicaldelete

Using the app is pretty simple:

1. Put the logicaldelete sub-folder in your Python Path.
2. Inherit from logicaldelete.models.Model for all models that you wish to share in this functionality.
3. Create and/or Register admins for each of these models using logicaldelete.admin.ModelAdmin

Meta options

You can specify deletion behaviour by using an inner class LogicalDeleteMeta, like so:

class YourModel(logicaldelete.models.Model):

    class LogicalDeleteMeta:
        delete_related = True
        safe_deletion = True
        delete_batches = False

Available Meta options

delete_related

If delete_related = True, when an objects referenced by a ForeignKey is deleted, it also deletes (or marked as deleted) the objects containing the ForeignKey. If delete_related = False related objects not deleted.

safe_deletion

safe_deletion means safe deletion related objects. If safe_deletion = True not delete related objects the instance of "plain" models class, but flagged as deleted related objects instances of logical deletion model class.

delete_batches

delete_batches = True means delete many-to-many relations.

If you want to save original deletion behaviour (for compatible with old code) you must set delete_related = False, and delete_batches = False

Additional Database Auditing Fields

Logical deletes are handled by date stamping a date_removed column. In addition, a date_created and date_modified columns will be populated as a convenience.

If you are migrating from an existing schema and you already have date_created or date_modified fields on your models, you can inheirit from logicaldelete.admin.LogicalDeleteModel to get only the delete-specific functionality.

Possible Extensions

You can easily subclass these two classes to provide generic and useful functionality to your models.

UUID Primary Key

I typically using UUID fields for my primary keys because they enable me to shard my tables if and when I need to, in addition, they provide an obfuscated id to my data (people can't determine how many of a certain object I have in my database, if I don't want them to know, but simply looking an an integer id in the URL).

Sequence Field

Many times I find it useful to have an integer field on my models that allow for and explicitly controlled sequencing. I normally implement this as a sort descending implementation where the data is sorted from high to low by sequence value.

In order to to implement this you'd subclass both the Model and ModelAdmin, where the Model would be an obvious simple addition of an IntegerField, the ModelAdmin, would override get_query_set, to do something like:

class SequencedModel(logicaldelete.models.Model):
    sequence = models.IntegerField()


class MyLogicalDeletedManager(logicaldelete.models.LogicalDeletedManager):
    def get_query_set(self):
        if self.model:
            qs = super(MyLogicalDeletedManager, self).get_query_set().filter(date_removed__isnull=True)
            if SequencedModel in inspect.getmro(self.model):
                qs = qs.order_by('-sequence')
            return qs