I had a slight variation on this thread - where to put some M2M field validation/deletion logic.
I have a purely model-based form where a checkbox’s value determines whether another field (it’s a M2M field) in the form should be NULL or keep its values to be saved in the database. So, following the appropriate separation of concerns as advocated below, I added logic in both the models' clean and save override methods. Neither approach set the other field to NULL when it should have been. The reason is the form still contained M2M values even though the model said to delete them (delete the set, actually). After a lot of trial and error, it turns out that the model’s save seems to be run BEFORE the form’s save. To me, that seems backwards. Shouldn’t the model’s processes (which are directly relate to the database, the ultimate data source) occur last and well before the form’s (which are merely an interaction with the user)? What was happening was my model’s delete actually did the deletions (those IDs were gone), but then the form’s processing came along afterwards and re-inserted them again (with brand new IDs). Can someone help me understand why Django has chosen this seemingly “inversion” of processing - first models’ processes, then forms’? And, perhaps more importantly, where should this either/or logic should be placed so it will take effect? Thanks very much, Jim Illback On Jul 13, 2019, at 11:48 PM, Mike Dewhirst <mi...@dewhirst.com.au<mailto:mi...@dewhirst.com.au>> wrote: Well yes it could be called multifaceted. Usually but not always the interface with the user is the form. You can have non-database fields as well as model fields so either way there has to be a full suite of validation functionality available in both types of forms. Luckily, model forms automatically call model.clean() for you. Unit tests don't though. You have deliberately call obj.clean() if you want to test things. obj.save() doesn't call obj.clean(). Actually, I also do a bit in view code too especially if there are non-database or hidden fields in the form. I know you are not supposed to validate data in a view for proper separation of concerns but it does keep my forms neater. The bottom line for me is that if I can imagine non-form access ... eg through an API ... then all validation possible has to be via model.clean() and the API has to remember to call clean() before saving every time there is a POST Hence I always put business rules validation in model.clean() and leave 'local' validation for the form. You are right. There are quite a few moving parts <ic_list_happy.png> Connected by Motorola Dean Karres <dean.kar...@gmail.com<mailto:dean.kar...@gmail.com>> wrote: Thank you. There are way more parts to this than I would have imagined. On Sat, Jul 13, 2019, 8:01 PM Mike Dewhirst <mi...@dewhirst.com.au<mailto:mi...@dewhirst.com.au>> wrote: On 14/07/2019 10:37 am, Dean Karres wrote: Hi, I am learning Django. I am using CBVs. My default "index.py" view is basically a dashboard for the app I am playing with. As my models and views become more complicated I want to be able to ask, for any model instance, is this instance "valid" or "complete". Valid means that all Required elements are present and have reasonable values. "Complete" means that an instance is "valid" but also some specific bits of additional info are also ok. For example I have a Student model that has name and address info. There is a ManyToMany relation to the Class(es) in which that Student is enrolled. A "student" instance is valid if the name and address fields are filled. A student is "complete" if the student is valid and has signed up for one or more classes. So, my question is: where should the valid and complete methods live? Should they be in the Student model or CBV? Someplace else? Does it matter? I like to put that sort of stuff into model methods then add model.clean() to call them and raise whatever error may be appropriate if they fail. https://docs.djangoproject.com/en/2.1/topics/forms/modelforms/#interaction-with-model-validation and https://docs.djangoproject.com/en/2.1/ref/models/instances/#validating-objects and https://docs.djangoproject.com/en/2.1/ref/models/instances/#django.db.models.Model.clean You can raise your own errors which inherit from ValidationError to fine tune the process. For example, I differentiate between BusinessRuleViolation and InvalidToken and a couple of others where that delivers better control. Cheers -- You received this message because you are subscribed to the Google Groups "Django users" group. To unsubscribe from this group and stop receiving emails from it, send an email to django-users+unsubscr...@googlegroups.com<mailto:django-users+unsubscr...@googlegroups.com>. To post to this group, send email to django-users@googlegroups.com<mailto:django-users@googlegroups.com>. Visit this group at https://groups.google.com/group/django-users. To view this discussion on the web visit https://groups.google.com/d/msgid/django-users/22801669-96ec-4a43-a264-fd50c2544604%40googlegroups.com<https://groups.google.com/d/msgid/django-users/22801669-96ec-4a43-a264-fd50c2544604%40googlegroups.com?utm_medium=email&utm_source=footer>. For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "Django users" group. To unsubscribe from this group and stop receiving emails from it, send an email to django-users+unsubscr...@googlegroups.com<mailto:django-users+unsubscr...@googlegroups.com>. To post to this group, send email to django-users@googlegroups.com<mailto:django-users@googlegroups.com>. Visit this group at https://groups.google.com/group/django-users. To view this discussion on the web visit https://groups.google.com/d/msgid/django-users/ajujeafh6d4qa4vvpfv2bxf9.1563085360028%40email.android.com<https://groups.google.com/d/msgid/django-users/ajujeafh6d4qa4vvpfv2bxf9.1563085360028%40email.android.com?utm_medium=email&utm_source=footer>. For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "Django users" group. To unsubscribe from this group and stop receiving emails from it, send an email to django-users+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/django-users/A2531CD5-E89E-4EB3-84C5-CF6CEB05E53D%40hotmail.com.
