CODEWITHSUNDEEP
pythondjangodjango-migrations
Undefined Variable
Undefined Variable

Reputation: 4267

How to create a new table using model

So I have this django installation in which there are a bunch of migration scripts. They look like so:

00001_initial.py
00002_blah_blah.py
00003_bleh_bleh.py

Now I know these are "database building" scripts which will take stuff defined in models.py and run them against the db to "create" tables and stuff.

I want to create a new table(so I created its definition in models.py). For this, I have copied another model class and edited its name and fields and it is all fine. Lets call this new model class 'boom'.

My question is now how do I "create" this boom table using the migration script and the boom model?

I am worried that I might accidentally disrupt anything that is already in DB. How do I run the migration to create only boom table? How do I create a migration script specifically for it?

I know that it has something to do with manage.py and running migrate or runmigration (or is it sqlmigrate?...im confused). While creating the boom table, I dont want the database to go boom if you know what I mean :)

Upvotes: 3

Views: 25402

Answers (4)

Rubén Vázquez
Rubén Vázquez

Reputation: 43

I solved it simply, changing the name of the new model to the original name, and then I checked if there is the table in the database, if not, I just create a new table with the old name with just a field like id. And then clear migrations and create new migrations, migrate and verify table was fixed in DB and has all missing fields. If it still doesn't work, then change the model name back to a new one. but when django asks you if you are renaming the model you should say NO to get the old one removed properly and create a new one.

This type of error usually occurs when you delete some table in dB manually, and then the migration history changes in the tables are lost. But it is not necessary to erase the entire database and start from scratch.

Upvotes: 1

RemcoGerlich
RemcoGerlich

Reputation: 31260

First, create a backup of your database. Copy it to your development machine. Try things out on that. That way it doesn't matter if it does go "boom" for some reason.

The first thing to do is

python manage.py showmigrations

This shows all the existing migrations, and it should show that they have been applied with an [X].

Then,

python manage.py makemigrations

Makes a new migration file for your new model (name 00004_...).

Then do

python manage.py migrate

to apply it. To undo it, go back to the state of migrations 00003, with

python manage.py migrate <yourappname> 00003

Upvotes: 10

wobbily_col
wobbily_col

Reputation: 11891

There are two steps to migrations in Django. 

./manage.py makemigrations

will create the migration files that you see - these describe the changes that should be made to the database.

You also need to run 

./manage.py migrate

this will apply the migrations and actually run the alter table commands in SQL to change the actual database structure.

Generally adding fields or tables won't affect anything else in the database. Be more careful when altering or deleting existing fields as that can affect your data.

The reason for two steps is so that you can make changes on a dev machine and once happy commit the migration files and release to your production environment. Then you run the migrate command on your production machine to bring the production database to the same state as your dev machine (no need for makemigrations on production assuming that your databases started the same).

Upvotes: 5

e4c5
e4c5

Reputation: 53734

My question is now how do I "create" this boom table using the migration script and the boom model?

 ./manage.py makemigrations

I am worried that I might accidentally disrupt anything that is already in DB.

The whole point of migrations, is that it doesn't

I know that it has something to do with manage.py and running migrate or runmigration

For more information please refer to : https://docs.djangoproject.com/en/1.10/topics/migrations/

And rest assured that your database will not go boom! :-)

Upvotes: 2

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