On 8/09/2018 9:09 PM, Jae Pil Choi wrote:
I'm asking this on the official Django community after I asked on
Stackoverflow because I still don't know what is the best practice for
this particular action.
(Original Question on Stackoverflowhere
<https://stackoverflow.com/questions/52225453/what-is-django-commend-equivalent-to-rails-rails-db-drop/52226394?noredirect=1#comment91407548_52226394>:
What is Django commend equivalent to Rails' $ rails db drop)
My scenario goes as follow:
1. I create 2 model class objects, Post, Product in models.py
2. Post has 2 attributes: post_title, post_text. Product has its own
but that's irrelevant.
3. I make migrations and migrate.
4. Then I go to /admin of my page and add some rows both on Post and
Product.
5. Now I remember that I I forgot to add an attribute post_author on
Post and adds it in models.py
6. If I make migrations, Django warns me that already existing rows
needs default values since they don't have this new attributes.
7. I don't want any post without an author so I want to drop this
existing rows and make it all again.
8. However, I don't want to lose any Product rows already created.
Here's the question: How do I drop ONLY Post table leaving Product and
my Superuser intact?
You need a custom migration ... ./migrations/remove_authorless_rows.py
def forwards_func(apps, schema_editor):
Model_class = apps.get_model("<app name>", "Model_class")
db_alias = schema_editor.connection.alias
Model_class.objects.using(db_alias).filter(author=None).delete()
class Migration(migrations.Migration):
dependencies = [
('<app name>', '<most recent previous successful migration>'),
]
operations = [
migrations.RunPython(
forwards_func,
),
]
This is off the top of my head so you would need to test it in a sandbox
and repair as required.
Original Stackoverflow post suggests manually removing db.sqlite3 file
and migrations files but I really don't think this is the way to go
and there must be some best practice or commend for this since Django
is already at 2.1.
If not, I think there must be a good reason not to have one and I want
to know why.
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