I am new to Django, and the tutorial directly applied this command without explanation.
After searching, I found out it's calling migrations in Django, but didn't understand it either as I am a complete newbie at this.
What does the python manage.py migrate command do exactly?
What are migrations?
If your database doesn't exist yet, migrate creates all the necessary tables to match your model definitions.
Otherwise if the database already exists, migrate updates the existing table definitions to match the model definitions -- i.e. maybe you added a field to one of your models, so migrate would add that column to the database table.
Related
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 have one model with the relevant fields setup. I ran manage.py migrate then it created the a table in my database. I then ran manage.py makemigrations so that it could create an initial migration file with prefix '0001'. I added another field to my model and then ran manage.py makemigrations again, which created another migration file with prefix '0002'. When I run manage.py migrate now it still looks at the first migration file and so throws out an error that the 'Table already exists'. How can I make it only look at the latest migration file so that it adds the new column to the table? I'm using MySQL.
This will never happen unless django detects (thinks) that the database has not been setup, and tries to initialise the tables with a schema.
Looks like your tables are already setup, but this is not known to django. That is why it tries to start applying the first migration - the table creation and schema is included in that.
You can use the --fake and --fake-initial options as per your specific problem, which tell django that the tables are already setup and ready, and to fake the migrations.
Useful links for more info:
django migrations - django documentation
django migrations, a primer - realpython
how to redo a migration after fake - stackoverflow
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 have recently updated my model, added a BooleanField to it however when I do python manage.py syncdb, it doesn't add the new field to the database for the model. How can I fix this ?
From Django 1.7 onwards
Django has built in support for migrations - take a look at the documentation.
For Django 1.6 and earlier
Django doesn't support migrations out of the box. There is a pluggable app for Django that does exactly that though, and it works great. It's called South.
Django currently does not do this automatically. Your options are:
Drop the table from the database, then recreate it in new form using syncdb.
Print out SQL for the database using python manage.py sql (appname), find the added line for the field and add it manually using alter table SQL command. (This will also allow you to choose values of the field for your current records.)
Use South (per Dominic's answer).
Follow these steps:
Export your data to a fixture using the dumpdata management command
Drop the table
Run syncdb
Reload your data from the fixture using the loaddata management command
As suggested in top answer, I tried using South, and after an hour of frustration with obscure migration errors decided to go with Django Evolution instead.
I think it's easier to get started with than South, and it worked perfectly the first time I typed ./manage.py evolve --hint --execute, so I'm happy with it.
Havent used django in a while, but i seem to remember that syncdb does perform alter commands on db tables. you have to drop the table then run again and it will create again.
edit: sorry does NOT perform alter.
In django 1.6
At first we have run - python manage.py sql <app name>
Then we have to run - python manage.py syncdb
If you run Django with Apache and MySQL, restart apache after making migration with makemigrations.
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.