Django 1.7 migrations won't recreate a dropped

问题:

Using Django 1.7 migrations.

I accidentally dropped a table in my database. I assumed that by running migration again this would recreate the table but no, Django states "No migrations to apply".

How to I get Django to recreate the table?

I have run:

> makemigrations - No changes detected
> migrate - No migrations to apply.

I have tried making a change to the model and running a new migration and it simply states that "Table 'x.test_customer' doesn't exist" which is correct, but what I was hoping it that it would recreate the table.

回答1:

Migrations check for differences in your models, then translates that to actions, which are translated to SQL. It does not automatically sync the db scheme with your models, and it has no way of knowing you dropped a table (it doesn't know about manual changes because, well, you're not supposed to do manual changes. That's the point)

The answer? a manual change requires a manual migration as well. What you need to do is simply write your own migration and manually tell south to re-build the table. It's not very difficult, The docs make it pretty easy. Just make something like this:

from django.db import migrations, models

class Migration(migrations.Migration):

    operations = [
        migrations.CreateModel("Foo"),
        migrations.AddField("Foo", "bar", models.IntegerField(default=0))
    ] 

You can probably look into the first migration file (the one that made the model in the first place) and copy paste almost all of it. Then all you have to do is run the migration like you always do

回答2:

Go to your database and find the table django_migrations. Delete all the rows which have app equals your app name.

Then do a makemigrations & migrate will work.

回答3:

Another solution I've found and works perfectly:

In django 1.7:

1. Delete your migrations folder

2. In the database: DELETE FROM django_migrations WHERE app = 'app_name'.

   You could alternatively just truncate this table.

3. python manage.py makemigrations

4. python manage.py migrate --fake

In django 1.9.5:

1. Delete your migrations folder

2. In the database: DELETE FROM django_migrations WHERE app = 'app_name'.

   You could alternatively just truncate this table.

3. python manage.py makemigrations app_name

4. python manage.py migrate

This works 100% for me!

回答4:

I actually found an easier way to do this. You fake that you rollback what doesn't exist, then you re-migrate. If your migration 0005 was the one where it creates the table:

python manage.py migrate myapp --fake 0004
python manage.py migrate myapp

Should be good after that!

If you need to skip later ones, you do this:

python manage.py migrate myapp --fake 0004
python manage.py migrate myapp 0005
python manage.py migrate myapp --fake

Should be good after that!

回答5:

Full disclaimer, this is a destructive operation in some cases, and I mostly use it to remigrate parts of the system without affecting the DB.

Have you tried doing it via the table django_migrations? Just remove the rows that map to the app label and the migration names in question and delete those rows.

+----+-----------------------+----------------------------------------------------------+---------------------+
| id | app                   | name                                                     | applied             |
+----+-----------------------+----------------------------------------------------------+---------------------+
|  1 | contenttypes          | 0001_initial                                             | 2015-03-07 16:32    |
| 30 | homepage              | 0001_initial                                             | 2015-04-02 13:30:44 |
| 31 | homepage              | 0002_auto_20150408_1751                                  | 2015-04-08 12:24:55 |
| 32 | homepage              | 0003_remove_mappinghomepagemoduleinventory_inventoryinfo | 2015-04-09 08:09:59 |
+----+-----------------------+----------------------------------------------------------+---------------------+

So now if i want to remove homepage, I can just delete row 30, 31, 32.

Of course since you dropped the tables too, you'd need to change django_content_type too:

+----+----------------------------------------+-----------------------+--------------------------------------+
| id | name                                   | app_label             | model                                |
+----+----------------------------------------+-----------------------+--------------------------------------+
|  1 | content type                           | contenttypes          | contenttype                          |
|  2 | session                                | sessions              | session                              |
|  3 | site                                   | sites                 | site                                 |
| 92 | master_homepagemodule_extrafields      | homepage              | masterhomepagemoduleextrafields      |
| 93 | mapping_homepagemodule_inventory       | homepage              | mappinghomepagemoduleinventory       |
| 94 | master_homepagemodule_inventoryfields  | homepage              | masterhomepagemoduleinventoryfields  |
| 95 | mapping_homepagemodule_inventoryfields | homepage              | mappinghomepagemoduleinventoryfields |
| 96 | master_homepagemodule                  | homepage              | masterhomepagemodule                 |
| 97 | mapping_homepagemodule_extrafields     | homepage              | mappinghomepagemoduleextrafields     |
+----+----------------------------------------+-----------------------+--------------------------------------+

So now you'd have to remove the tables that you need to remigrate need by dropping the rows for those tables.

I've used this when time was scarce and we needed a quick dirty fix, or when playing around in development.
Hope it helps you too!

回答6:

The simplest way to do this on django >= 1.9 is to run the following:

./manage.py migrate app_name zero

That will remove your tables and revert all migrations.

回答7:

OK, so what I did was not to mess with migrations. Seems like I get in trouble every so often with migrations. And in this case, trying to replay migrations got me nowhere. Might not have helped that there were some South-vintage migrations as well as the newer 1.7 stuff.

environment: postgres 9.3

Basically, I restored an old backup of my database into an empty database. Then I brought up the restore target in the postgres admin utility and copy/pasted the create tables from each table's description (I had only 4 to go). Switched over to my test database & ran it in pg's sql utility.

I dunno, I don't think it is unreasonable to drop a table manually if you are having issues with it (looked to me as if my id field's sequence was not working), as long as you can live with losing your data. Migrations should be resilient in that use case.

回答8:

In my case in django 2.0.2 for recreating dropped table I needed to comment my models in myapp and then migrate with --fake and uncomment my models and migrate without --fake A little different from raul answer:

1. Delete your migrations files in your desired app
2. Thanks to raul answer: In the database: DELETE FROM django_migrations WHERE app = 'app_name'.
3. comment codes in models.py and all this models usage in views, signals and etc (to prevent error).
4. python manage.py makemigrations YOUR_APP_NAME
5. python manage.py migrate --fake
6. un-comment what you commented in step 3
7. python manage.py makemigrations YOUR_APP_NAME
8. migrate without --fake: python manage.py migrate

This should solve some users problem.

回答9:

Just ran into this while building a little app learning django. I wanted to create a non-null column for an existing table. There were three steps:

1. drop the table
2. remove the record in django_migrations
3. remove the migration for the table in question
   • if you run "python manage.py makemigrations posts" before this step you still get the "You are trying to add a non-nullable field "

For an actual application you'd need to supply a default value as others have pointed out.