I changed the name of the attributes of one of my models. As soon as I made the change in the models.py script, I tried to migrate it using makemigrations command, but it kept giving me an error that the email field is non-nullable and the database needs something to populate the existing rows. So I tried to reverse the previous migrations and ran the command python3 manage.py <app_name> zero.
After this the previous non-nullable field error was resolved at the command line but as soon as I submit the form at the browser, I run into this Operational error.
The crux of the matter is how to make changes to the attributes of one of the models in models.py and deal with the consequent migrations ?
You might want to delete your database or running the python manage.py flush commands when making such changes. If you do not want to do that, just add a one-time default (make sure its the right type).
Related
I am trying to simply add a boolean field to a model in my database following the simple rules:
- add field to model
- python manage.py makemigrations app
- python manage.py migrate app
Works all but 99% of the time. So during the second step (makemigrations), with my newly added field in my model raring to go, i get an error:
django.db.utils.OperationalError: (1054, "Unknown column 'model.field' in 'field list'")
Excellent. its not letting me make migrations by adding a new field..... because it cant find the field that I am trying to newly add... makes perfect sense!
Anyway, I have gone as far as deleting all my migrations, removing my new field, making migrations again, migrating... all fine - so now i have only 1 migration file (0001)...
Follow the same steps as above... ERROR
Am i missing something ridiculous here? I mean, adding a field to a model is very simple, and I have done it probably 1000 times. Why does Django tease me so
EDIT: Answer:
OK I have done it.
After deleting the migrations file, truncating the migrations table and migrating with 0001_initial.py, I made an empty migrations file (python manage.py makemigrations --empty app) and added the field in manually.... then I migrated and it worked! Baffled at this to be honest, but at least the change has been made:
Delete all migration files
Truncate the django_migrations table
comment the new boolean field
run python manage.py makemigrations
run python manage.py migrate --fake
run python manage.py makemigrations --empty app
add field in manually to the empty migrations file in the operations:
migrations.AddField('modelName', 'fieldName', models.BooleanField(default=False)),
run python manage.py migrate
uncomment the new boolean field so it represents what you made in the migrations operations
Disclaimer- Follow this only on local system, for production do understand the steps and then execute.
Kindly follow these steps:
Delete all migration files
Truncate the django_migrations table
comment the new boolean field
run python manage.py makemigrations
run python manage.py migrate --fake
Uncomment the boolean field
run python manage.py makemigrations
run python manage.py migrate
Generally these steps solve any kind of migration problem
An another reason can be if you are using django_rest_framework then the serialiser too needs to be updated as per your model change.
This is an issue that has persisted with me and lead me down a lot of rabbit holes dropping tables etc. A simple solution I have found is answering "N" when django asks you if you are renaming a field of that model (when running makemigrations). What that then essentially performs is a deletion of your previous field and creates the new field. Be careful as you may lose data on existing field so this works with fields which are either new or relatively easy to 'refill' their data required. You may need to run --fake if you get an error with regards to not being able to 'drop field' when migrating after makemigrations. If you would like to go back to your migration state before the problem you may need to delete the migrations you have done since then and try the above solution.
Update:
I did the above for a Boolean field and my data was kept. Even though I said N, it seems as if it is essentially a renaming.
Another source of the problem: I have a ModelForm based on the model. The ModelForm definition defines two extra fields. I had to comment out those two fields from the Form definition before doing the migration steps. Once the migration was done, I un-commented the two fields.
I have a Postgres database full of data. And I made several changes to my Django app models.
mange.py makemigrations worked fine and created the migration files. But manage.py migrate execute only one file. And when I launch it again it doesn’t execute the rest as if they are already applied.
I deleted the migration files that were not applied and did another makemigration but it says no changes detected.
Any ideas how to reflect the models changes on the database without losing the data ?
Thanks
Django keeps track of which migrations it has applied already, so when you run the migrate command it will execute only the migrations that Django thinks that are missing.
I deleted the migration files that were not applied and did another makemigration but it says no changes detected.
This was a bad idea, it will make your migrations inconsistent.
If you want to go back in time, instead of deleting migrations, the proper way to do this is by reverting migrations. You can use the same migrate command and specify to which migration point you want your database model to be.
Check this answer for further information about reverting migrations; django revert last migration
I have trouble with django model migrations.
I have some models in my app, and I already have some data inside.
When I added some models in my application, and I run makemigrations, the app report that there is no change.
I know that sometimes some errors came when migrate, so I delete django_migrations table in my database and run makemigrations again, and now program found my new fields.
The problem now is that if I run migrate system tell me that some tables already exist. (Which is ok and correct, because they do). I don't want to delete those tables, because I have data already inside.
I can't run migrate --fake, because program will think that I already have all the tables, which is not true.
So, I am looking for a way to tell the program : run migration, if table exist skip it. (--fake it)
Another question is why is this happening to me, that makemigrations don't recognise my changes (some cache problems,...)?
How about doing this way ?
python manage.py makemigrations
(Skip this step if you have already have migration file ready)
It will create migrations for that package lets say with a name like 0001_initial.py
Edit the file manually so that you delete all models there except that was already created in database.
Now you do a fake migration. This will sync your database with models.
python manage.py migrate --fake
Then run makemigrations again to have rest of the tables created along with a new migration file.
python manage.py makemigrations
Regarding your other question, Why makemigrations didn't recogonize your models can be because of reasons like:
Migrations for those changes are already there in some migration file.
You missed it to mention package_name in INSTALLED_APPS but i believe you did it here.
every time you make changes to your models, try these steps :
python manage.py makemigrations [your app name]
then:
python manage.py migrate
it should work fine. but remember if you have already data(rows) in your tables you should specify the default value for each one the queries.
if not, Django prompt you to specify the default value for them
or you can just try to use blank=True or null=True in your fields like below :
website = models.URLField(blank=True)
the possible cause or this is that you have another migration in the same folder starts with the same prefix... maybe you make another migration on the same table on another branch or commit so it's saved to the db with the same prefix ie: 00010_migration_from_commit_#10, 00010_migration_from_commit_#11
the solution for this is to rename the migration file like this 00011_migration_from_commit_#11
I tried to edit the related migration file and commented the part where it creates that specific column, then ran python manage.py migrate
The main problem is the existing tables that are disabling the migration of the new tables, so the solution is straight-forward:
** Try to add managed = False to the existing dB so it won't be detected by migrate
** Redo it for all existing old tables :
class Meta:
managed=False
It sometimes gets boring when we have a lot of tables in the same application but it works perfectly!
In addition to adding/deleting/modifying field to model, Django also detects changes when I add or modify methods to the model.
So my question is should I run makemigrations every time I change or add a new method in models ?
When you add/change model methods, then you don't need to run ./manage makemigrations and ./manage.py migrate.
But whenever you edit your model fields (adding a new one, changing an existing one or altering any of the arguments it takes) then you should always run migrations.
First of all,
./manage makemigrations
will create (migration_number).py files in your app migrations folders. These lines of code are nothing but statements which help in creating actual fields in your respective database similar to SQL statements.
In order to execute the migration which was created using the previous command, we will run the following command,
./manage.py migrate
On migrate your new model fields will be reflected in database if there are no errors
I started a django 1.8 project, which uses the migrations system.
Somehow along the way things got messy, so I erased the migrations folders and table from the DB, and now I'm trying to reconstruct them, with no success.
I have three apps (3 models.py files), and the models reflect the tables EXACTLY!
The best approach that I've found so far was:
Erase all migrations folders. Done!
Delete everything from the django_migrations table. Done!
Run python manage.py makemigrations --empty <app> for every app. Done!
Run python manage.py migrate --fake. Done! (although it works only if I run it after every makemigrations command.
Now I add a new field, run the makemigrations command, and I receive the following error:
django.db.utils.OperationalError: (1054, "Unknown column 'accounts_plan.max_item_size' in 'field list'")
I've been burning HOURS on this thing. How the h**l can I initialize the migrations so I can continue working without migration interruptions every time?
Why is it so complicated? Why isn't there a simple one-liner: initiate_migrations_from_schema?
EDIT:
Now things get even nastier. I truncated the django_migrations table and deleted all the migrations folder.
Now I try to run python manage.py migrate --fake-initial (something I found in the DEV docs), just so it sets up all of Django's 'internal' apps (auth, session, etc) and I'm getting:
(1054, "Unknown column 'name' in 'django_content_type'").
Now, this "column" is not a real column. It's a #property defined in Django's contenttypes app. WHAT IS GOING ON HERE? Why is it identifying the name property as a real column?
Finally got it to work, although I don't know why and I hope it will work in the future.
After doing numerous trials and going through Django's dev site (link).
Here are the steps (for whoever runs into this problem):
Empty the django_migrations table: delete from django_migrations;
For every app, delete its migrations folder: rm -rf <app>/migrations/
Reset the migrations for the "built-in" apps: python manage.py migrate --fake
For each app run: python manage.py makemigrations <app>. Take care of dependencies (models with ForeignKey's should run after their parent model).
Finally: python manage.py migrate --fake-initial
After that I ran the last command without the --fake-initial flag, just to make sure.
Now everything works and I can use the migrations system normally.
I'm sure I'm not the only one who encounters this issue. It must be documented better and even simplified.
Update for Django 1.9 users:
I had this scenario again with a Django 1.9.4, and step 5 failed.
All I had to do is replace --fake-initial with --fake to make it work.
django ..., 1.8, 1.9, ...
What you want to achieve is squashing existing migrations and use replacement for them.
How to do it right without using any command when releasing (a case without impact on database and coworkers).
For every app, get rid of its migrations folder:
mv <app>/migrations/ <app>/migrationsOLD/
For each that app run: python manage.py makemigrations <app>.
Customize each new migration:
if you have a complex app, or more apps and related models between them, to avoid CircularDependencyError or ValueError: Unhandled pending operations for models:
prepare second empty migration in <app> 0002_initial2.py (put there dependency to app_other::0001_initial.py and <app>::0001_initial.py as well - all ForeignKey, M2M related to models created in 0001 migration step in other apps)
All must be in order - sometimes it will require more migrations to prepare. Take care of dependencies attribute here in each Migration.
take care of initial values - verify yourself all RunPython actions from migrationsOLD and copy the code to new initial migration if needed.
(optional for --fake-initial) Add initial=True to all new Migration classes (0002 too if was added).
Add replaces attribute in new Migration class. (like own custom a squashmigrations). Put there all old migrations from <app>
Verify everything with makemigrations.
assert "No changes detected"
Check if migrate -l show [x] everywhere
assert similar:
[X] 0001_initial
[X] 0002_initial2 (102 squashed migrations)
Example:
For old:
0001_initial.py
0002_auto.py
...
0103_auto.py
prepare:
0001_initial.py
0002_initial2.py (optional but sometimes required to satisfy dependency)
and add to replacesto last one (0002 here, can be 0001):
replaces = [(b'<app>', '0002_auto.py'), ..., (b'<app>', '0103_auto.py')]
0001_initial.py should be named the same way as old one.
0002_initial2.py is new one, but it's a replacement for old migrations so Django will treat it as loaded.
I've run into this scenario but I've never had to drop the database to solve it. Typically I delete the migrations folder from the app's, and remove the migration entries from the database.
I would try to run make migrations one app at a time. If any of the app's rely upon other tables obviously add them last.
Also I usually just run, python manage.py makemigrations then just python manage.py migrate Even with the initial migration it should work fine with Django 1.7 and 1.8.
If you are using routers, might be a problem there. Check method allow_migrate if it is executed in a right way in routers.py. Try to set return value always to be True, and check whether it resolves problem,
def allow_migrate(self, db, app_label, model_name=None, **hints):
return True