We are a team of developers working on Django project. We are facing issues with django migrations. if one developer makes changes in model and runs makemigrations>migrate sequence it generates some sqls in migrations directory. Now when other developer pulls the code, and run the same sequence it's putting code in bad state. We've been clearing our migrations directory locally to get rid of the issue, and sometimes clear all the data. Not sure what we're doing incorrectly. Please suggest the right way of using django migrations.
Note - All of us use separate instances of DB in local machine.
makemigrations just create files
By running makemigrations, you’re telling Django that you’ve made some changes to your models (in this case, you’ve made new ones) and that you’d like the changes to be stored as a migration.
Migrations are how Django stores changes to your models (and thus your database schema) - they’re just files on disk. You can read the migration for your new model if you like; it’s the file polls/migrations/0001_initial.py.
Under Version Control, after you push the migrations file, for example, 0001_initial.py. Other developers just pull the file then run
python manage.py sqlmigrate your_app 0001 # to see what happen
python manage.py migrate your_app 0001
More about the Version Control:
Version control
Because migrations are stored in version control, you’ll occasionally come across situations where you and another developer have both committed a migration to the same app at the same time, resulting in two migrations with the same number.
Don’t worry - the numbers are just there for developers’ reference, Django just cares that each migration has a different name. Migrations specify which other migrations they depend on - including earlier migrations in the same app - in the file, so it’s possible to detect when there’s two new migrations for the same app that aren’t ordered.
When this happens, Django will prompt you and give you some options. If it thinks it’s safe enough, it will offer to automatically linearize the two migrations for you. If not, you’ll have to go in and modify the migrations yourself - don’t worry, this isn’t difficult, and is explained more in Migration files below.
Related
I've got a Django app with a lot of out-of-date migrations. I'd like to remove the old migrations and start fresh.
The app has 14 different "migrations" folders.
Here is what a few of them look like:
Is it safe to remove all the contents from each of these folders? Or, do I have to make sure to only remove some of the files -- and if so which files?
You should never just delete migrations before unapplying them, or it will be a nightmare when you want to apply new migrations.
To unapply migrations you should do the following:
Use the python manage.py migrate your_app_name XXXX in case you want to unapply migrations after the XXXX migration. Otherwise use python manage.py migrate your_app_name zero to completely unapply all migrations.
Remove the .pyc files under /migrations/_pycache_/ that you have unapplied.
Remove the .py files under migrations/ that you have unapplied.
Now you can create new migrations without any headaches.
If what you're looking for is to squash all the migrations into one, do the steps above removing all migrations and then run python manage.py makemigrations your_app_name to create a single migration file. After that just run python manage.py migrate your_app_name and you're done.
That depends. If you have a production database (or any database you cannot simply drop and recreate), then the answer is no, you cannot safely remove migrations.
If you do not have any permanent databases, then yes, you can remove all migrations, run python manage.py makemigrations --initial and it will create fresh migrations based on your current models.
Also, you should check if any of the migrations are custom data migrations written by hand. If there are any, you might want to keep those.
The .pyc files are generally safe to remove, provided the related .py files are still there.
your first screenshot is not Django and looks like a JS project of some sort.
The json and js files are unrelated to the django migrations as well as __pycache__ folder. You can delete all off them.
If you mean "previously applied and no longer needed as the project only needs the latest version of the migrations" you don't want to remove but squash them instead with squashmigrations which reduces the files you have to two, init file and the initial migration file, this way your project still works.
If by remove you mean you no longer need them because you already changed the models so much that the previous migrations aren't even used other than being applied and unapplied without ever being used, doesn't matter, go to step 2 and do that instead of deleting the files manually. When you create migrations on your applications one by one, you also create migration dependency tree, well, django does. And it is really hard to keep track of after some point, if you try to delete everything thinking you can create new migration files with ease, trust me as someone who experienced otherwise, it does not work like that. It is way simpler to let django handle the migration squashing, it optimizes the migration meaning that it also deletes the unused ones in your final state.
More to read at: https://docs.djangoproject.com/en/2.2/topics/migrations/#migration-squashing
Having marked one of the answers provided previously as being accepted, here is a summary of a few things I learned:
Deleting Django migrations is generally a bad idea.
Django keeps track of what's in your db through these migration files, as well as through a table it creates in your db, and if you delete any of this Django will start throwing errors on migrate that can be hard to fix.
I was getting some of those hard-to-fix errors. Here is what I did to fix it:
Ran migrate on the production server.
When I got an error, it would tell me how the db was out of sync with what Django expected. I corrected that manually by directly editing the db with an sql client.
E.g. If it said a key existed that wasn't supposed to exist, I deleted the relevant index from the indicated table.
Or if it said a table existed that wasn't supposed to exist, I backed up the table to a file, and deleted the table. Migrate then created the table, and then I repopulated it with data from the backup.
In the case of many-to-many tables, once Django had re-created them, I deleted all the new Django-created tables, and restored them from a backup created on my local dev system, which had already had all the latest migrations run on it.
Eventually I was able to complete all migrations successfully.
I have a feeling I lucked out and the above won't work in all cases! I've learned a lot about Django and migrations and will be much more careful about this in the future.
when you import from third app:
there are 2 step uninstall it
there are use the 'django_celery_beat' app for example.
step1: clean table
python .\manage.py migrate django_celery_beat zero
step2: remove app from INSTALLED_APPS
there are done!!!
this is django document on this.
How to Reset Migrations
if you are using linux/unix os then you can fire this command. delete all migration directory.
find . -path "/migrations/.py" -not -name "init.py" -delete
find . -path "/migrations/.pyc" -delete
I've deployed my Django application for a while now, but all this time I've kept migrations out of souce control. What I did was run makemigrations and migrate twice-- once in development, and once in production. So now how can I seamlessly put my migrations into source control? Theoretically the migrations should be the same (given my models.py files haven't changed), but how would I go about matching my migrations up without accidentally overriding something?
I'm not sure if I understand the problem...
Django keeps track of which migrations have been applied using the database. But it uses the names, not the contents. So as long as you're not changing the contents of migrations that have already been applied, you should be good.
I have accidently deleted one of migrations folders and and have no backup for it.
What are my options?
DB is postgres. Right now everything is OK.(I have moved instead migration folder I have on my DEV server with SQL lite) So I am just getting red message on server that not all migrations have been applied.
But next time if i run migration i will be in trouble.
What is my way out?
Migrations are mainly for backward compatibility, and tracking/versioning of the changes to models/database. If you do not really care about historical changes, etc.. then you can just delete the migrations directory and do:
python manage.py makemigrations <app_name>
This creates the initial migrations (like starting from a clean slate) - and moving forward you can track the historical migrations moving forward. More on this can be read here
Now, when you run the migrations, you can do
python manage.py migrate <app_name> --fake-initial
to fake the initial migration.
Now might be a good time to have a version control on your application
Use version control.
You are not the first developer to delete important files, but often recovery takes less than a second - thanks to version control systems (also called revision control systems). Please stop everything else and install and use one of Git, Mercury or Subversion.
Don't use FTP
It's totally. I mean totally insecure. Always use SFTP
Don't use sqlite3 for local with other db for production
sqlite doesn't enforce strict type checking. Postgresql on the other hand is very particular about it. Additionally sqlite only has a subset of the functionality that's found on postgresql. Last but not least different RDBMS have different intricacies. If you use one locally and another in production, there is always a chance that your code will break when you deploy to live
Managing without the migration files
This is not a big loss as long as your database is in sync with your models.
If you database is not in sync with your models, you can use
./manage.py inspectdb
to recreate local models that represent the actual structure in the db. Then you do makemigrations and migrate (as explained by karthik) on the generated models.
Then replace that with your live models and do the step again.
Actually we are group of 3 people working on the same project, and each one individually make changes in django database. After running migrations in individual machine, it creates migration file for each migration. When someone pushes updated code in remote git repository, it creates conflict with others' migrations of same name.
Because of this reason, I lost my whole data once. Kindly give suggestions what should I do with this migration thing?
here's what i do: whenever I want to fetch from remote i check if a duplicate migration will be fetched. (we have a script that checks for all migration directories if there are filenames which have the same starting number.) if that is the case, I 'merge' the migrations, usually like this:
Find the last migration before the duplicate, let's say it's migration 000X
Make sure you are on your local source version, before the duplicate is added.
migrate back to after migration n:
python manage migrate app 000X
pull the new version including the duplicates.
remove your duplicate migrations
run schemamigration
python manage schemamigration --auto
Now you should get a new migration adding your model changes on top of the changes that were made in the migration you pulled.
I have a few projects with lots of South migrations, including ones that contain a fair amount of custom SQL that need to be run in a specific order. After upgrading to Django 1.7, this is the recommendation on how to convert a project to use South (from the Django documentation):
If you already have pre-existing migrations created with South, then the upgrade process to use django.db.migrations is quite simple:
Ensure all installs are fully up-to-date with their migrations.
Remove 'south' from INSTALLED_APPS.
Delete all your (numbered) migration files, but not the directory or __init__.py - make sure you remove the .pyc files too.
Run python manage.py makemigrations. Django should see the empty migration directories and make new initial migrations in the new format.
Run python manage.py migrate. Django will see that the tables for the initial migrations already exist and mark them as applied without running them.
In short, "wipe your existing migrations and Django will take care of the rest".
What is not mentioned here is what to do when existing South migrations don't only consist of model changes, but instead contain direct SQL, data migrations, etc, that need to be run in order. In this case, the auto-generated Django migrations will miss a lot of things, since not all of these changes are obvious from introspecting a models file.
Ideally, one would be able to run the existing migrations using South, and then have Django migrations take over. What might be the best way to go about this? If this is not possible or very much not recommended, what is the best alternative?
Maybe this post can help you. Essentially you have to:
Change your current migration directory from 'migrations' to 'south_migrations'
Update your settings with this line
SOUTH_MIGRATION_MODULES = {
'your_app': 'your_project.your_app.south_migrations',
}