I am building a Django web application and I dropped the table django_migrations using psql command line and I want to recreate it.
To recreate django_migrations simply use
./manage.py migrate --fake
But please be careful with that as mentioned here:
If you break something, nobody can help you probably, because the
migration system will not know the current state of the database more.
Therefore do a backup, write notes, use a sandbox and work precisely.
Django migrate --fake and --fake-initial explained
Related
I am using flask-migrate to update the changes in my database. I ran this command. and then this command
$python manage.py db init
$python manage.py db migrate
I get the error below
alembic.util.exc.CommandError: Can't locate revision identified by 'e462fd034cc1'
I looked on stackoverflow for similar problems where it was suggested to deleted the migrations folder which i did but still same error is coming again and again.
What should i do.
Your database is out of sync with your migrations repository. For some reason the latest migration id stored in the database is not the migration id of a migration in your repository. This means that you probably deleted or modified the migration repository by hand and made it inconsistent with the current state of your database.
If this is a scratch database, maybe deleting and running the migrations again will fix the problem and give you a valid database.
Just see what is your last migration number.
Open migrations/versions folder in any file manager and sort by date.
For me, for example, it e222b725dce9_.py
Then change the value in version_num column in alembic_version table
Note that I delete underscrore in the end
Then run python manage.py db migrate and python manage.py db upgrade
All must pass successfully
So I was being stupid and I went to delete one of the tables in my django app so opened up psql and ran "Drop table ;" and dropped the table. Then I deleted my model and ran "python manage.py migrate" and I get this error...
django.db.utils.ProgrammingError: relation "textchange_myuser" does not exist
among other stuff above it.
So now I can't delete the table properly and I can't get it back. What do I do?
Thanks.
I deleted a table from postgres and then django was unable to detect the change. I tried everything but django didn't created a new table. Finally I fixed this with some alternate way.
login to your database create table manually.
- Get the create command from django itself.
python manage.py sqlmigrate 'yourapp' 001
this will give you the initial command django used to create the table.
one by one get all the migrations and execute commands on database by command line.
As per my comment, in your situation you might run:
python manage.py migrate yourapp --fake
to "fake" applying the migration but not actually alter your database.
You can read more HERE
Hope this helps.
I switched from MySQL to PostgreSQL and running migrations and it is a bit strange after MySQL. When I run ./manage.py migrate on a clean db, whenever the migration comes to a field which is ForeignKey or any other relation field, which is not yet created in db, it raises an error and stops. In MySQL you just run migrate and it does all for you, MySQL created these non-existing fields.
So can I somehow to control the execution of migrations like, please postgres go and do that migration first and that second and so on, because otherwise all you gotta do is do migrate manually one by one.
You can explicitly set dependencies between migrations, as described in the docs.
I am using Django to build a website with MySQL. Now as I am learning so I need to change the Model very often so I want that all tables get cleared and new table get created.
But syncdb doesn't touch existing tables. Is there any better way to handle this problem?
If you don't care about data:
Best way would be to drop the database and run syncdb again. Or you can run:
For Django >= 1.5
python manage.py flush
For Django < 1.5
python manage.py reset appname
(you can add --no-input to the end of the command for it to skip the interactive prompt.)
If you do care about data:
From the docs:
syncdb will only create tables for
models which have not yet been
installed. It will never issue ALTER
TABLE statements to match changes made
to a model class after installation.
Changes to model classes and database
schemas often involve some form of
ambiguity and, in those cases, Django
would have to guess at the correct
changes to make. There is a risk that
critical data would be lost in the
process.
If you have made changes to a model
and wish to alter the database tables
to match, use the sql command to
display the new SQL structure and
compare that to your existing table
schema to work out the changes.
https://docs.djangoproject.com/en/dev/ref/django-admin/
Reference: FAQ - https://docs.djangoproject.com/en/dev/faq/models/#if-i-make-changes-to-a-model-how-do-i-update-the-database
People also recommend South ( http://south.aeracode.org/docs/about.html#key-features ), but I haven't tried it.
Using Django Extensions, running:
./manage.py reset_db
Will clear the database tables, then running:
./manage.py syncdb
Will recreate them (south may ask you to migrate things).
I think Django docs explicitly mention that if the intent is to start from an empty DB again (which seems to be OP's intent), then just drop and re-create the database and re-run migrate (instead of using flush):
If you would rather start from an empty database and re-run all
migrations, you should drop and recreate the database and then run
migrate instead.
So for OP's case, we just need to:
Drop the database from MySQL
Recreate the database
Run python manage.py migrate
Quickest (drops and creates all tables including data):
./manage.py reset appname | ./manage.py dbshell
Caution:
Might not work on Windows correctly.
Might keep some old tables in the db
You can use the Django-Truncate library to delete all data of a table without destroying the table structure.
Example:
First, install django-turncate using your terminal/command line:
pip install django-truncate
Add "django_truncate" to your INSTALLED_APPS in the settings.py file:
INSTALLED_APPS = [
...
'django_truncate',
]
Use this command in your terminal to delete all data of the table from the app.
python manage.py truncate --apps app_name --models table_name
I've already defined a model and created its associated database via manager.py syncdb. Now that I've added some fields to the model, I tried syncdb again, but no output appears. Upon trying to access these new fields from my templates, I get a "No Such Column" exception, leading me to believe that syncdb didn't actually update the database. What's the right command here?
As of Django 1.7+, built-in migrations support, allows for database schema migrations that preserve data. That's probably a better approach than the solution below.
Another option, not requiring additional apps, is to use the built in manage.py functions to export your data, clear the database and restore the exported data.
The methods below will update the database tables for your app, but will completely destroy any data that existed in those tables. If the changes you made to your app model do not break your old schema (for instance, you added a new, optional field) you can simply dump the data before and reload it afterwards, like so:
Django 1.4.15 and earlier
python manage.py dumpdata <your_app> > temp_data.json
python manage.py reset <your_app>
python manage.py loaddata temp_data.json
Django 1.5 and newer
python manage.py dumpdata <your_app> > temp_data.json
python manage.py sqlclear <your_app> | python manage.py dbshell
python manage.py syncdb
python manage.py loaddata temp_data.json
(The reset command was deprecated and then removed in Django 1.5)
If your changes break your old schema this won't work - in which case tools like South or Django Evolution are great.
As of Django 1.7, you can now do this with native migrations. Just run
python manage.py makemigrations <your app name>
python manage.py migrate
Seems like what you need is a migration system. South is really nice, working great, has some automation tools to ease your workflow. And has a great tutorial.
note: syncdb can't update your existing tables. Sometimes it's impossible to decide what to do automagicly - that's why south scripts are this great.
Django's syncdb doesn't alter existing tables in the database so you have to do it manually. The way I always do it is:
Change the model class first.
Then run: manage.py sql myapp.
Look at the sql it prints out and see how it represented the change you are going to make.
Make the change manually using your database manager.
Check to see if everything worked correctly using the admin site.
If you are using sqllite a good manager is the firefox plugin: link
Another tool would be django evolution. No table dropping needed in most cases.
django evolution
Just install it as any other django app and run:
python manage.py evolve --hint --execute
deseb is a great tool for that.
Having it installed, you can write ./manage.py sqlevolve and it'll generate sql commands necessary to keep the database structure in sync with your models.
You need to drop your tables before you can recreate them with syncdb.
If you want to preserve your existing data, then you need to unload your database,
drop your tables, run syncdb to build a new database, then reload your old data into your new tables.
There are tools that help with this. However, in many cases, it's just as easy to do it manually.
For versions 1.4.1 and above users the command has changed to
python manage.py flush
Please read the official document before using it as it will delete all your data.