Django auto-deletes field related to MySQL Transactions

[RyanW]

I have a Django site I'm developing, which I've connected to a MySQL db.  I haven't deployed into production yet, as I'm still working on a couple of things, however I leave the server running in development for initial data entry. 

I've noticed that some of the records already inputted gets deleted, seemingly randomly. I enabled logging on MySQL and found logs like the following:

6798 Connect
ryan45@cobb.eyes.uab.edu on downswebdb2

6798 Query
SET NAMES utf8

6798 Query
set autocommit=0

6798 Query
set autocommit=1

6798 Query
SET SESSION TRANSACTION ISOLATION LEVEL READ COMMITTED

6798 Query
SELECT `Epe_epe`.`id`, `Epe_epe`.`epe_type`, `Epe_epe`.`epe_type2_id`, `Epe_epe`.`epe_date`, `Epe_epe`.`epe_ani`, `Epe_epe`.`epe_ani2_id`, `Epe_epe`.`epe_apn`, `Epe_epe`.`epe_apn2_id`, `Epe_epe`.`epe_weight`, `Epe_epe`.`epe_drug_type1`, `Epe_epe`.`epe_drug1`, `Epe_epe`.`epe_dose1`, `Epe_epe`.`epe_amount1`, `Epe_epe`.`epe_route1`, `Epe_epe`.`epe_time1`, `Epe_epe`.`epe_drug_type2`, `Epe_epe`.`epe_drug2`, `Epe_epe`.`epe_dose2`, `Epe_epe`.`epe_amount2`, `Epe_epe`.`epe_route2`, `Epe_epe`.`epe_time2`, `Epe_epe`.`epe_drug_type3`, `Epe_epe`.`epe_drug3`, `Epe_epe`.`epe_dose3`, `Epe_epe`.`epe_amount3`, `Epe_epe`.`epe_route3`, `Epe_epe`.`epe_time3`, `Epe_epe`.`epe_drug_type4`, `Epe_epe`.`epe_drug4`, `Epe_epe`.`epe_dose4`, `Epe_epe`.`epe_amount4`, `Epe_epe`.`epe_route4`, `Epe_epe`.`epe_time4`, `Epe_epe`.`epe_drug_type5`, `Epe_epe`.`epe_drug5`, `Epe_epe`.`epe_dose5`, `Epe_epe`.`epe_amount5`, `Epe_epe`.`epe_route5`, `Epe_epe`.`epe_time5`, `Epe_epe`.`epe_drug_type6`, `Epe_epe`.`epe_drug6`, `Epe_epe`.`epe_dose6`, `Epe_epe`.`epe_amount6`, `Epe_epe`.`epe_route6`, `Epe_epe`.`epe_time6`, `Epe_epe`.`epe_iso_start`, `Epe_epe`.`epe_iso_end`, `Epe_epe`.`epe_o2_end`, `Epe_epe`.`epe_start1`, `Epe_epe`.`epe_start2`, `Epe_epe`.`epe_start3`, `Epe_epe`.`epe_start4`, `Epe_epe`.`epe_start5`, `Epe_epe`.`epe_start6`, `Epe_epe`.`epe_start7`, `Epe_epe`.`epe_start8`, `Epe_epe`.`epe_hr1`, `Epe_epe`.`epe_hr2`, `Epe_epe`.`epe_hr3`, `Epe_epe`.`epe_hr4`, `Epe_epe`.`epe_hr5`, `Epe_epe`.`epe_hr6`, `Epe_epe`.`epe_hr7`, `Epe_epe`.`epe_hr8`, `Epe_epe`.`epe_spo2_1`, `Epe_epe`.`epe_spo2_2`, `Epe_epe`.`epe_spo2_3`, `Epe_epe`.`epe_spo2_4`, `Epe_epe`.`epe_spo2_5`, `Epe_epe`.`epe_spo2_6`, `Epe_epe`.`epe_spo2_7`, `Epe_epe`.`epe_spo2_8`, `Epe_epe`.`epe_temp1`, `Epe_epe`.`epe_temp2`, `Epe_epe`.`epe_temp3`, `Epe_epe`.`epe_temp4`, `Epe_epe`.`epe_temp5`, `Epe_epe`.`epe_temp6`, `Epe_epe`.`epe_temp7`, `Epe_epe`.`epe_temp8`, `Epe_epe`.`epe_etco2_1`, `Epe_epe`.`epe_etco2_2`, `Epe_epe`.`epe_etco2_3`, `Epe_epe`.`epe_etco2_4`, `Epe_epe`.`epe_etco2_5`, `Epe_epe`.`epe_etco2_6`, `Epe_epe`.`epe_etco2_7`, `Epe_epe`.`epe_etco2_8`, `Epe_epe`.`epe_rr1`, `Epe_epe`.`epe_rr2`, `Epe_epe`.`epe_rr3`, `Epe_epe`.`epe_rr4`, `Epe_epe`.`epe_rr5`, `Epe_epe`.`epe_rr6`, `Epe_epe`.`epe_rr7`, `Epe_epe`.`epe_rr8`, `Epe_epe`.`epe_comment` FROM `Epe_epe` WHERE `Epe_epe`.`id` = 1508

6798 Query
set autocommit=0

6798 Query
DELETE FROM `Epe_epe` WHERE `Epe_epe`.`id` IN (1508)

6798 Query
commit

6798 Query
set autocommit=1

6798 Quit

Where Epe_epe is from a model called Epe in my Django app. 

As far as I know, no user is performing delete commands on these records, so can I assume Django is performing these deletes in the background?  What would a trigger possibly be for these deletes?

Thank you

[Matthew Pava]

Check your source code for any delete commands.

This might also be your authentication backend.  Which one are you using?

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[RyanW]

I have a button to delete a record by the user, displayed inside a template as:

<td><a href={% url 'epedelete' epe.id %}><input class="btn btn-danger" type="button" value="Delete" /></a></td>

and the function in views.py

def delete(request, part_id=None):

    obj = epe.objects.get(id=part_id)

    obj.delete()

    return HttpResponseRedirect(reverse('epe_home'))

Other than that, I have some ForeignKey restraints on_delete to preserve integrity, like so:

    epe_ani2 = models.ForeignKey(

        Subjects,

        on_delete=models.PROTECT,

        null=True,

        blank=True

    )

As for the authentication backend, I'm using the default provided by Django:

['django.contrib.auth.backends.ModelBackend']

Thank you for the help!

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[Matthew Pava]

It doesn’t seem like Django would be doing this.

Do you have any other apps connected to the database?

You’ll probably want to surround your URL in quotation marks.  <a href=”{% url ‘epedelete’ epe.id %}”>

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[RyanW]

Yes, I honestly don't see how Django could be doing this either.  The only I could think of was user deletion, but no one has claimed to have done so.

No other apps are connected.

Thanks for the tip!!

[Joel]

You could have a signal which captures all these and logs its origin.

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[Matthew Pava]

And make sure your form is posting to the save view and not the delete view.  Maybe show us your template.

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[RyanW]

Hi Matthew and Joel. Thanks for your help.

I'm attaching the models.py, views.py and templates for your reference.  I'm drawing a blank on the implementation that could trigger a delete.

Thanks again

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[Matthew Pava]

I can’t see anything wrong with what you’ve presented.  Try generating a new database and using that.  See if you still get random deletes on that database.

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[RyanW]

I've tried two separate MySQL db's on two separate servers.  They both have given me deletes.  What's strange is that I've set up a local copy on my laptop with both a local Postgres DB and MySQL connection, and I don't get the same deletes.

I've narrowed it down that it must be something the users are doing to trigger these deletes, based on logs that would've put them active during a time of a delete.

[Matthew Pava]

In that case, is there something in a template that is possibly calling the delete view based on some user trigger, i.e. some Javascript function?

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[C. Kirby]

Is this happening to production users? It is probably because their browser is doing pre-fetch of links to speed up their UX. GET request are considered by the browser to be safe (non-destructive) and ideally idempotent. YOu should _never_ put a destructive action behind a GET, it should always be behind a POST or (even better if you are going the full REST route) DELETE.

[RyanW]

Yes, it is. Are you referring to 'delete' method in my views?

[Mark Phillips]

Just a wild guess - do you have a cascade delete in your models that is causing the deletion? Is a user deleting another object, and that is triggering a cascade delete on a different model?

Mark

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[RyanW]

Hi Mark,

I did at one point, but I don't any longer ( I use RESTRICT now). 

Would you guys mind if I attached a copy of the app for review?

Thank you!

[C. Kirby]

The delete method in your views, yes, but also how you build the button. You should use a form with a hidden field (the id to delete), and the button ("Delete") should be the form submit. Then on the view side you should use a standard form handler (if request.POST....etc) to handle things. What is probably happening is the browser is automatically following the <a> tag to do prefetching, and causing the record to delete. Browsers will not prefetch "POST" verbs (so, a form post)

[RyanW]

Thanks for the info. Do you know of a way that I can confirm this is happening?

Best,

- Ryan