Thank you for your input, Jarek. Assuming I have an existing model, adding
models.CharField(blank=True, max_length=150) to it, doesn't invoke the questioner on current master. Changing this field to models.CharField(max_length=150) doesn't call the questioner either. Looking at the SQL Django generates, the first change results in ALTER TABLE "example_mymodel" ADD COLUMN "name2" varchar(150) DEFAULT '' NOT NULL; ALTER TABLE "example_mymodel" ALTER COLUMN "name2" DROP DEFAULT; and the second in a noop. I'm trying to understand what change you're proposing in order to figure out if going forward with your proposal is something we should do. Cheers, Markus On Sun, Sep 11, 2016 at 05:08:38AM -0700, Jarek Glowacki wrote:
Mm, convenience over strict correctness. Perhaps all that's needed is a slight rephrasing of the prompt and we can have both? Adding field with no `blank=True` and no `null=True`: You are trying to add a non-nullable field '%s' to %s without a default; we can't do that (the database needs something to populate existing rows). [provide default | cancel] Removing `null=True` from field: You are trying to change the nullable field '%s' on %s to non-nullable without a default; we can't do that (the database needs something to populate existing rows). [provide default | fix later | cancel] Removing `blank` from field: ?? (I only skimmed the code; not sure if this even opens up questioner) This kind of implies to the user that they're doing something wrong. Maybe if, for string fields, it read something more along the lines of: You are adding/altering a field without setting `blank=True`. This will populate existing rows with emptystring despite it being an invalid form input. Are you sure? [yes | let me provide a one-time default for existing rows | cancel] So basically changing "you can't do this!" (exception-esque) to "are you sure you want this?" (warning-esque). Anyway I think I'll leave it here. I've exhausted my discussion points now, and you already resolved my particular use case back in the ticket, so I no longer feel so strongly about this to continue trying to push for a change (though am willing to submit a PR if any of the suggested changes are approved). Cheers, On Saturday, September 10, 2016 at 10:08:27 AM UTC+10, Tim Graham wrote:Sure, but I don't think that use case should take priority. It's not much work to type an empty string into the questioner if that's what you want. If we remove the prompt, it's significantly more work (editing a migration file or using RunPython) for a developer to set a non-empty value. On Friday, September 9, 2016 at 7:19:37 PM UTC-4, Jarek Glowacki wrote:Instances created afterwards, via `MyModel.objects.create()`, with this field unset won't pass form validation either. The use case is where this field is not expected to appear on a Django form. On Friday, September 9, 2016 at 11:58:38 PM UTC+10, Tim Graham wrote:If blank=False, then a new column with a non-blank value means that all existing objects won't pass form validation. Therefore, I don't see why a prompt for a value isn't helpful. On Friday, September 9, 2016 at 6:42:02 AM UTC-4, Jarek Glowacki wrote:I made a rant/ticket regarding the hidden usage of `blank` here: #27197 <https://code.djangoproject.com/ticket/27197#ticket>. In short, I don't think that `blank` should dictate whether or not the migration questioner runs. Building on this, I don't think it should run for for string-type fields at all. If they have `default` set, use that for existing rows. Else if they have `null=True`, set existing rows to `NULL`. Else, set existing rows to empty string. See linked rant/ticket for some (hopefully) compelling arguments.. Thoughts?-- You received this message because you are subscribed to the Google Groups "Django developers (Contributions to Django itself)" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/django-developers. To view this discussion on the web visit https://groups.google.com/d/msgid/django-developers/60bf1464-7e70-41c4-b8de-b201af84b4b7%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
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