Unexpected behavior on delete of model

[Joel Mathew]

Situation:

I have two Model classes, in two different apps which are part of the same project. class doctor defined in appointments.models is a set of attributes associated with a doctor, like name, username, email, phone etc. class DoctorProfilePic is a Model defined in clinic.models, which has a StdImageField which stores images. doctor has a One to One mapping to DoctorProfilePic.

    class doctor(models.Model):

        docid = models.AutoField(primary_key=True, unique=True) # Need autoincrement, unique and primary

        name = models.CharField(max_length=35)

        username = models.CharField(max_length=15)

        ...

        profilepic = models.ForeignKey(DoctorProfilePic, blank=True, null=True, on_delete=models.CASCADE)

        ...

    class DoctorProfilePic (models.Model):

        id = models.AutoField(primary_key=True, unique=True)

        name = models.CharField(max_length=255, blank=True)

        pic = StdImageField(upload_to="data/media/%Y/%m/%d", blank=True, variations={

            'large': (600, 400),

            'thumbnail': (150, 140, True),

            'medium': (300, 200),

        })

        doc = models.ForeignKey('appointments.doctor', blank=True,

                                null=True, on_delete=models.CASCADE)

        

Anticipated response:

When user selects one of the profile pics from a selection box, and clicks Delete, django is supposed to delete the picture from the collection of pictures uploaded by the doctor.

Problem:

When the delete button is clicked, django deletes both the picture and the doctor, instead of just the former.

Code:

    def removeprofpic(request, docid):

        docid = int(docid)    

        if not IsOwnerorSuperUser(request, docid):

            return HttpResponse("You dont have permissions to do this.")

        doc = doctor.objects.get(docid = docid)

        if request.method == 'POST':

            print(request.POST)

            picid = int(request.POST.get('profilepic'))

            print(f'doc:{doc} picid:{picid}')

            pic = DoctorProfilePic.objects.get(doc = doc, id =picid)

            pic.delete()

            msg = f"Successfully removed profile picture."

        else:

            msg = "Not a valid POST"

        return HttpResponse(msg)

Now I'm guessing my problem is in defining the on_delete=models.CASCADE? Can someone explain what I've done wrong?

Sincerely yours,

 Joel G Mathew

[Matthew Pava]

You’ll want to review this reference:

https://docs.djangoproject.com/en/2.1/ref/models/fields/#django.db.models.ForeignKey.on_delete

 

You probably want the option on doc to be SET_NULL.

 

Actually, I suggest some overall cleanup.

Your model names should follow a standard convention.  Django practices the camel case convention.  (CamelCase)

Also, you have a ForeignKey where you probably just want a OneToOneField.

Use related_name to have a reverse relationship.  In my proposal below, you can access the profile picture just like you could before.

I would have just let Django handle the primary key field without changing the name of it.

 

doctor.profile_pic

 

    class Doctor(models.Model):

        name = models.CharField(max_length=35)

        username = models.CharField(max_length=15)

 

    class DoctorProfilePic (models.Model):

        name = models.CharField(max_length=255, blank=True)

        pic = StdImageField(upload_to="data/media/%Y/%m/%d", blank=True, variations={

            'large': (600, 400),

            'thumbnail': (150, 140, True),

            'medium': (300, 200),

        })

        doctor = models.OneToOneField(Doctor, blank=True,

                                null=True, on_delete=models.SET_NULL, related_name="profile_pic")

 

 

…and after saying all that, I wouldn’t make a separate model for the profile picture.  This is what I would do:

    class Doctor(models.Model):

        name = models.CharField(max_length=35)

        username = models.CharField(max_length=15)

        profile_pic = StdImageField(upload_to="data/media/%Y/%m/%d", blank=True, variations={

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[Saurabh Agrawal]

 

    class Doctor(models.Model):

        name = models.CharField(max_length=35)

        username = models.CharField(max_length=15)

 

    class DoctorProfilePic (models.Model):

        name = models.CharField(max_length=255, blank=True)

        pic = StdImageField(upload_to="data/media/%Y/%m/%d", blank=True, variations={

            'large': (600, 400),

            'thumbnail': (150, 140, True),

            'medium': (300, 200),

        })

        doctor = models.OneToOneField(Doctor, blank=True,

                                null=True, on_delete=models.SET_NULL, related_name="profile_pic")

 

Setting on_delete to SET_NULL doesn't make much sense here, I think. This implies that if a doctor is deleted, the profile pic will be preserved, with the FK to doc being set to NULL in db (which doesn't seem desirable). I think here CASCADE should work good and will not have the issue that the OP is facing.

 

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[Joel]

I think you made a typo in the code. doctor can't be a Foreign key for class Doctor. Anyway I get your point, and this is the same way I solved it yesterday.

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[Joel]

Ignore the last post. Formatting blues in my main editor.

[Todor Velichkov]

Right now, your doctor will be deleted if its ProfilePicture gets deleted. I'm pretty sure you don't want to do that.

I believe this is what you are looking for:

    class Doctor(models.Model):
        # When the profile picture gets delete, clear doctors profile picture (set to NULL)
        profilepic = models.ForeignKey(DoctorProfilePic, blank=True, null=True, on_delete=models.SET_NULL)


    class DoctorProfilePic (models.Model):
        # When the doctor gets deleted, delete its picture too (CASCADE)
        # PS. Do not allow orphan ProfilePics (w/o a doctor), i.e. blank=False, null=False
        doc = models.ForeignKey('appointments.Doctor', on_delete=models.CASCADE)

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[Joel Mathew]

Yes, thank you, Todor.

Yesterday night, I ended up doing exactly this.

Sincerely yours,

 Joel G Mathew

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