Django: models last mod date and mod count

Question

I have a django model called Blog.

I'd like to add a field to my current model that is for last_modified_date. I know how to set a default value, but I would like somehow for it to get automatically updated anytime I modify the blog entry via the admin interface.

Is there some way to force this value to the current time on each admin site save?

Also would there be some way to add a mod_count field and have it automatically calculated on each modify of the admin site blog entry?

Answer 1

Create a datetime field in your model. Have it update whenever it is saved. This requires you to use the auto_now_add option:

class DateTimeField([auto_now=False, auto_now_add=False, **options])

DateTimeField.auto_now_add¶

Automatically set the field to now every time the object is saved. Useful for "last-modified" timestamps. Note that the current date is always used; it's not just a default value that you can override.

It should look something like this:

class Message(models.Model):
    message = models.TextField()
    active = models.BooleanField(default=True)
    created_at = models.DateTimeField(auto_now_add=True)

Model field reference

For the second part, I think you have to overload

ModelAdmin.save_model(self, request, obj, form, change)

As James Bennett describes here. It will look something like this:

class EntryAdmin(admin.ModelAdmin):

def save_model(self, request, obj, form, change):
    if change:
        obj.change_count += 1
    obj.save()

Answer 2

There's a number of ways you can increase the edit count each time it's saved.

The model itself has a save() method, and the admin model has a model_save() method.

So for example, let's say you wanted it to increment when it was edited with the admin tool....

models.py:

class MyModel(models.Model):
    edit_count = models.IntegerField()
    # ... rest of model code here...


admin.py:

class MyModelAdmin(admin.ModelAdmin)
    def save_model(self, request, obj, form, change):
        if not change:
            obj.edit_count = 1
        else:
            obj.edit_count += 1
        obj.save()

You could do similar code off of the model save() event as well.

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Something else you may be interested in is django-command-extensions. It adds 2 fields which may be helpful to you:

• CreationDateTimeField - DateTimeField that will automatically set it's date when the object is first saved to the database.

• ModificationDateTimeField - DateTimeField that will automatically set it's date when an object is saved to the database.