Broken quotes with multiple databases

[David-Wobrock]

Hi,

On a Django project that defines multiple databases, the quotes are broken.

Defining

DATABASES = {
    'mysql': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'mydb',
        [...]
    },
    'postgresql': {
        'ENGINE': 'django.db.backends.postgresql',
        'NAME': 'db',
        [...]
   },
}

One app has a migration that looks like

    operations = [
        migrations.AddField(
            model_name='a',
            name='not_null_field',
            field=models.IntegerField(default=1),
        ),
        AddDefaultValue(
            model_name='a',
            name='not_null_field',
            value=1,
        )
    ]

Launching the tests, which will set up both databases, we get the error

django.db.utils.ProgrammingError: syntax error at or near "`"                                                                                                                                               
LINE 1: ALTER TABLE `app_add_not_null_column_followed_by_default_a` ... 

---

Investigation: Introspecting the SQL queries that are sent to the database:

• to the MySql database we send

  ALTER TABLE `app_add_not_null_column_followed_by_default_a` ADD COLUMN `not_null_field` integer DEFAULT %s NOT NULL                                                                                         
  ALTER TABLE `app_add_not_null_column_followed_by_default_a` ALTER COLUMN `not_null_field` DROP DEFAULT                                                                                                      
  SELECT engine FROM information_schema.tables WHERE table_name = %s                                                                                                                                          
  ALTER TABLE `app_add_not_null_column_followed_by_default_a` ALTER COLUMN `not_null_field` SET DEFAULT '1';

and to the postgresql DB:

ALTER TABLE "app_add_not_null_column_followed_by_default_a" ADD COLUMN "not_null_field" integer DEFAULT %s NOT NULL                                                                                         
ALTER TABLE "app_add_not_null_column_followed_by_default_a" ALTER COLUMN "not_null_field" DROP DEFAULT                                                                                                      
ALTER TABLE `app_add_not_null_column_followed_by_default_a` ALTER COLUMN `not_null_field` SET DEFAULT '1';

where the last line obviously is incorrect.

Thank you for your time :) David

[David-Wobrock]

And funnily enough, since we have badly isolated logic, when you change the order of the databases in the settings, it works for some cases (even though, the dict are unordered. From one version of Python to another, the behaviours changes). Probably because mysql accepts the same quotes as postgresql, but postgresql does not accept the mysql quotes :+1:

So I got a workaround in some edge cases at least ;)