I had a table in Postgres called user that was a custom model. I then switched over to the default Django User class, but there have been issues because of the name overlap. How can I either wipe the previous table, or wipe the entire DB (still in testing, so not a big deal) to start over?
The simplest would be to execute a DROP TABLE statement directly in your database prompt, remember that Django models are just like any other table for your database
dropdb --help
Run this in the terminal
Related
I'm working in a development environment on a flask-app with a Postgres 10 database that has ~80 tables. There are lots of relationships and ForeignKeyConstraints networking it all together.
It was working fine with Flask-Migrate. I'd bootstrapped and migrated up to this point with ~80 tables. But, I wanted to test out some new scripts to seed the database tables, and thought it would be quickest to just drop the database and bring it back up again using Flask-Migrate.
In this process, the migration folder was deleted, so I just started over fresh with a db init. Then ran db migrate. I manually fixed a few imports in the migrate script. Finally, I ran db upgrade.
However, now with all these 80 create_table commands in my migrate script, when I run db_upgrade, I receive an error:
sqlalchemy.exc.ProgrammingError: (psycopg2.ProgrammingError) relation "items" does not exist
I receive this error for every Child table that has a ForeignKeyConstraint if the Child table is not in an order which is below the Parent table in the migration file.
But, the autogenerated script from db migrate has the tables sorted alphabetically, ordered by table name.
Referring to documentation, I don't see this importance of sort order mentioned.
Bottom line is, it seems I'm either forced to write a script to sort all these tables in an order where the Parent table is above the Child table. Or else, just cut and paste like a jigsaw puzzle until all the tables are in the required order.
What am I missing? Is there an easier way to do this with Flask-Migrate or Alembic?
After researching this, it seems flask-migrate and/or Alembic does not have any built-in methods to resolve this sort order issue. I fixed it by cutting and pasting the tables in an order which ensured the Parent table was above the child tables in the migration file.
I've just encountered this myself, and could not find a better and/or official answer.
My approach was to separate the table creation from the creation of foreign key constraints:
Edit Alembic's auto-generated migration script: In each table create operation, remove all lines creating foreign key constraints
Run Alembic's upgrade command (tables are created, minus the FK constraints, of course)
Run Alembic's migrate command (additional migration script created, that adds all FK constraints)
Run Alembic's upgrade command (FK constraints added to tables)
I've faced some problems when using flask-sqlalchemy and flask-migrate, I solved it using python interactive shell.
>>> from yourapp import db, create_app
>>> db.create_all(app=create_app())
Check this link to get more information.
Happy coding...
When my Django project is installed, the db is created and my fixtures are used to populate the db, this normal work flow works great. However at a specific time (after the db and its content are created) I want to alter an existing record in the db.
Is there a way to programmatically alter a record in an existing database table? Perhaps using python manage.py sqlall? If possible I want to avoid a 'hackish' solution like writing a little script that will run a sql alter command.
You could create a python script, import your Django models and do the changes just like within a Django application. Then execute that script on the given time.
I just tested it myself. I had Django models, and there have already been instances of the models in the database.
Then I added a dummy integer field to a model and ran manage.py syncdb. Checked the database, and nothing happened to the table. I don't see the extra field added in.
Is this the expected behavior? What's the proper way of modifying the model, and how will that alter the data that's already in the database?
Django will not alter already existing tables, they even say so in the documentation. The reason for this is that django can not guarantee that there will be no information lost.
You have two options if you want to change existing tables. Either drop them and run syncdb again, but you will need to store your data somehow if you want to keep it. The other options is to use a migrations tool to do this for you. Django can show you the SQL for the new database schema and you can diff that to the current version of the database to create the update script.
You could even update your database mannually if it is a small change and you don't want to bother with migrations tools, though I would recommend to use one.
Please use south for any kind of changes to get reflected to your database tables,
here goes the link for using south
Link for South documentation
I rewrote a lot of my models, and since I am just running a test server, I do ./manage.py reset myapp to reset the db tables and everything has been working fine.
But I tried to do it this time, and I get an error,
"The full error: contraint owner_id_refs_id_9036cedd" of relation "myapp_tagger" does not exist"
So I figured I would just nuke the whole site and start fresh. So i did ./manage.py flush then did a syncdb this did not raise an error and deleted all my data, however it did not update the database since when I try to access any of my_app's objects, i get a column not found error. I thought that flush was supposed to drop all tables. The syncdb said that no fixtures were added.
I assume the error is related to the fact that I changed the tagger model to having a foreignkey with a name owner tied to another object.
I have tried adding related_name to the foreignkey arguments and nothing seems to be working.
I thought that flush was supposed to drop all tables.
No. According to the documentation, manage.py flush doesn't drop the tables. Instead it does the following:
Returns the database to the state it was in immediately after syncdb was executed. This means that all data will be removed from the database, any post-synchronization handlers will be re-executed, and the initial_data fixture will be re-installed.
As stated in chapter 10 of The Django Book in the "Making Changes to a Database Schema" section,
syncdb merely creates tables that don't yet exist in your database — it does not sync changes in models or perform deletions of models. If you add or change a model's field, or if you delete a model, you’ll need to make the change in your database manually.
Therefore, to solve your problem you will need to either:
Delete the database and reissue manage.py syncdb. This is the process that I use when I'm still developing the database schema. I use an initial_data fixture to install some test data, which also needs to be updated when the database schema changes.
Manually issue the SQL commands to modify your database schema.
Use South.
I'm now making unit-tests for already existing code. I faced the next problem:
After running syncdb for creating test database, Django automatically fills several tables like django_content_type or auth_permissions.
Then, imagine I need to run a complex test, like check the users registration, that will need a lof ot data tables and connections between them.
If I'll try to use my whole existing database for making fixtures (that would be rather convinient for me) - I will receive the error like here. This happens because, Django has already filled tables like django_content_type.
The next possible way is to use django dumpdata --exclude option for already filled with syncdb tables. But this doesn't work well also, because if I take User and User Group objects from my db and User Permissions table, that was automatically created by syncdb, I can receive errors, because the primary keys, connecting them are now pointing wrong. This is better described here in part 'fixture hell', but the solution shown there doensn't look good)
The next possible scheme I see is next:
I'm running my tests; Django creates test database, makes syncdb and creates all those tables.
In my test setup I'm dropping this database, creating the new blank database.
Load data dump from existing database also in test setup
That's how the problem was solved:
After the syncdb has created the test database, in setUp part of the tests I use os.system to access shell from my code. Then I'm just loading the dump of the database, which I want to use for tests.
So this works like this: syncdb fills contenttype and some other tables with data. Then in setUp part of tests loading the sql dump clears all the previously created data and i get a nice database.
May be not the best solution, but it works=)
My approach would be to first use South to make DB migrations easy (which doesn't help at all, but is nice), and then use a module of model creation methods.
When you run
$ manage.py test my_proj
Django with South installed with create the Test DB, and run all your migrations to give you a completely updated test db.
To write tests, first create a python module calle, test_model_factory.py In here create functions that create your objects.
def mk_user():
User.objects.create(...)
Then in your tests you can import your test_model_factory module, and create objects for each test.
def test_something(self):
test_user = test_model_factory.mk_user()
self.assert(test_user ...)