I have a Django application with a My-SQL database. recently I alter the table_name with the help of MySQL query in the MySQL-shell, after this when I run makemigration and migrate command terminal says "No changes detected". how can i resolve this issue and create again this table with help of Django makemigration and migrate?
can I delete a table from MySQL, any possibility will Django create it again?
If you renamed your table outside Django - you will have to tell Django the new table name like so (using the Meta class):
class Model(models.Model):
name = models.CharField(max_length=255)
class Meta:
db_table = 'new_table_name'
To re-create your table using existing model you need to reset migration for that app to zero and then run migration again
python manage.py migrate APP_NAME zero
python manage.py migrate APP_NAME
It's because the migrations table managed by django doesn't reflect the correct db schema since it was already modified outside of django. If you don't have any important data you can do a migration rollback or recreate the table by hand.
The best way to dela with this is to rename your table back to the original name. Then create a blank migration inside your app and recreate the sql commands you did in the shell inside that migration file. That way django can keep track of the database schema.
You should change the name of the table in models.py not in MySQL shell.
From
class MyModel(models.Model):
...
To
class ThisModel(models.Model):
...
Or Create Proxy Model :
class ThisModel(MyModel):
class Meta:
proxy = True
verbose_name = "ThisModel"
I am migrating to django-oscar2.1
I have forked catalogue app, it has some existing migrations. Newly added field is_public is in migration #10. I have a custom migration #5 which is using create_from_breadcrumbs method. So when I tried to run migrate on fresh db migration#5 trigger error is_public field not exists in db.
create_from_breadcrumbs
Oscar loads a model with latest state which contains is_public in models but not in db.
In migration #5 I am loading model like this
Category = apps.get_model("catalogue", "Category")
You cannot use create_from_breadcrumbs in a migration like that. The reason for this is explained in Django's documentation on migrations - that the version of the model used in external code may be different from the one that this migration expects - which is why it fails.
If you want to create model objects as part of your migration you need to use the historic version of the model in the migration. This means defining your own version of create_from_breadcrumbs, and using the historic version of the model as suggested by the Django documentation:
def create_from_breadcrumbs_for_migration(apps, schema_editor):
Category = apps.get_model('catalogue', 'Category')
# Perform logic to create categories here.
class Migration(migrations.Migration):
dependencies = [
('catalogue', '0004_xxxx'),
]
operations = [
migrations.RunPython(create_from_breadcrumbs_for_migration),
]
That said, I would argue that migrations are not meant for this sort of data population in the first place. You would in my view be better off writing a separate management command for this, which you run after the migrations have been applied.
our website lists local city events. It's Django-based so there's a lot of code related to 'event' model. Until now, we work only in one city and so all the events mean to be local.
Now we need to extend the website to another city. This means 'event' model gets a new attribute 'city', and our middleware will set a global value CurrentCity based on geoip.
We need to extend 'event' model so it would filter only records where 'city' attribute equals to CurrentCity value. There is too much code in different views and models working with the 'event' so we can't update each module.
Is there any single place to patch that would make our 'event' model aware of the CurrentCity value?
Depending a lot in your structure and Django version I think you have 2 options.
South
The best one is to install the application "South". I don't know if you already know it or you're using it but I think it should be your first option.
In case you're not using it, you should do this steps:
Install with pip install South
Create your first migration with:
python manage.py schemamigration YOURAPPNAME --initial
You need to fake this migration, because you have already the fullfilled database so you need to do:
python manage.py migrate YOURAPPNAME --fake
Add the new field to the model Event in the file models.py
Generate the new migration to make South create the new field in your database with:
python manage.py schemamigration YOURAPPNAME --auto
Final step, execute the migration created with:
python manage.py migrate YOURAPPNAME
Tips
--initial for the first migration --auto for the rest
The initial migration is faked because you already have tables in your database, if you try to migrate without the fake it will return error "Table already exists"
New Model City
Another option, in case you can't modify your actual Model, or maybe if it's too messy, another option is to generate an externa Model City like this:
class City(models.Model):
event_foreign = models.ForeignKey(Event)
event_many = models.ManyToManyField(Event, blank=True, null=True)
name = models.CharField....
postal_code = models.CharField....
# etc...
I don't know wich is optimal for you, a Foreign Key or a ManyToMany, depends if a City can have more than 1 Event or no, it's your choice.
When you have a model like this you can access from this City model to the Event (because of the ForeignKEy or ManyToMany) but this relation goes also in the other direction, if you have an Event you can get the City/cities related to it I'm gonna show two examples:
Example 1 using Foreign Key
city = City.objects.get(id=1)
city.event # Returns event
event = Event.objects.get(id=1)
event.city # Returns city
Example 2 using Many to Many
city = City.objects.get(id=1)
city.event.all() # Returns a list of events
event = Event.objects.get(id=1)
event.city_set.all() # Returns a list of cities
I'd prefer not to destroy all the users on my site. But I want to take advantage of Django 1.5's custom pluggable user model. Here's my new user model:
class SiteUser(AbstractUser):
site = models.ForeignKey(Site, null=True)
Everything works with my new model on a new install (I've got other code, along with a good reason for doing this--all of which are irrelevant here). But if I put this on my live site and syncdb & migrate, I'll lose all my users or at least they'll be in a different, orphaned table than the new table created for my new model.
I'm familiar with South, but based on this post and some trials on my part, it seems its data migrations are not currently a fit for this specific migration. So I'm looking for some way to either make South work for this or for some non-South migration (raw SQL, dumpdata/loaddata, or otherwise) that I can run on each of my servers (Postgres 9.2) to migrate the users once the new table has been created while the old auth.User table is still in the database.
South is more than able to do this migration for you, but you need to be smart and do it in stages. Here's the step-by-step guide: (This guide presupposed you subclass AbstractUser, not AbstractBaseUser)
Before making the switch, make sure that south support is enabled in the application
that contains your custom user model (for the sake of the guide, we'll call it accounts and the model User).
At this point you should not yet have a custom user model.
$ ./manage.py schemamigration accounts --initial
Creating migrations directory at 'accounts/migrations'...
Creating __init__.py in 'accounts/migrations'...
Created 0001_initial.py.
$ ./manage.py migrate accounts [--fake if you've already syncdb'd this app]
Running migrations for accounts:
- Migrating forwards to 0001_initial.
> accounts:0001_initial
- Loading initial data for accounts.
Create a new, blank user migration in the accounts app.
$ ./manage.py schemamigration accounts --empty switch_to_custom_user
Created 0002_switch_to_custom_user.py.
Create your custom User model in the accounts app, but make sure it is defined as:
class SiteUser(AbstractUser): pass
Fill in the blank migration with the following code.
# encoding: utf-8
from south.db import db
from south.v2 import SchemaMigration
class Migration(SchemaMigration):
def forwards(self, orm):
# Fill in the destination name with the table name of your model
db.rename_table('auth_user', 'accounts_user')
db.rename_table('auth_user_groups', 'accounts_user_groups')
db.rename_table('auth_user_user_permissions', 'accounts_user_user_permissions')
def backwards(self, orm):
db.rename_table('accounts_user', 'auth_user')
db.rename_table('accounts_user_groups', 'auth_user_groups')
db.rename_table('accounts_user_user_permissions', 'auth_user_user_permissions')
models = { ....... } # Leave this alone
Run the migration
$ ./manage.py migrate accounts
- Migrating forwards to 0002_switch_to_custom_user.
> accounts:0002_switch_to_custom_user
- Loading initial data for accounts.
Make any changes to your user model now.
# settings.py
AUTH_USER_MODEL = 'accounts.User'
# accounts/models.py
class SiteUser(AbstractUser):
site = models.ForeignKey(Site, null=True)
create and run migrations for this change
$ ./manage.py schemamigration accounts --auto
+ Added field site on accounts.User
Created 0003_auto__add_field_user_site.py.
$ ./manage.py migrate accounts
- Migrating forwards to 0003_auto__add_field_user_site.
> accounts:0003_auto__add_field_user_site
- Loading initial data for accounts.
Honestly, If you already have good knowledge of your setup and already use south, It should be as simple as adding the following migration to your accounts module.
# encoding: utf-8
from south.db import db
from south.v2 import SchemaMigration
from django.db import models
class Migration(SchemaMigration):
def forwards(self, orm):
# Fill in the destination name with the table name of your model
db.rename_table('auth_user', 'accounts_user')
db.rename_table('auth_user_groups', 'accounts_user_groups')
db.rename_table('auth_user_permissions', 'accounts_user_permissions')
# == YOUR CUSTOM COLUMNS ==
db.add_column('accounts_user', 'site_id',
models.ForeignKey(orm['sites.Site'], null=True, blank=False)))
def backwards(self, orm):
db.rename_table('accounts_user', 'auth_user')
db.rename_table('accounts_user_groups', 'auth_user_groups')
db.rename_table('accounts_user_user_permissions', 'auth_user_user_permissions')
# == YOUR CUSTOM COLUMNS ==
db.remove_column('accounts_user', 'site_id')
models = { ....... } # Leave this alone
EDIT 2/5/13: added rename for auth_user_group table. FKs will auto update to point at the correct table due to db constraints, but M2M fields' table names are generated from the names of the 2 end tables and will need manual updating in this manner.
EDIT 2: Thanks to #Tuttle & #pix0r for the corrections.
My incredibly lazy way of doing this:
Create a new model (User), extending AbstractUser. Within new model, in it's Meta, override db_table and set to 'auth_user'.
Create an initial migration using South.
Migrate, but fake the migration, using --fake when running migrate.
Add new fields, create migration, run it normally.
This is beyond lazy, but works. You now have a 1.5 compliant User model, which just uses the old table of users. You also have a proper migration history.
You can fix this later on with manual migrations to rename the table.
I think you've correctly identified that a migration framework like South is the right way to go here. Assuming you're using South, you should be able to use the Data Migrations functionality to port the old users to your new model.
Specifically, I would add a forwards method to copy all rows in your user table to the new table. Something along the lines of:
def forwards(self, orm):
for user in orm.User.objects.all():
new_user = SiteUser(<initialize your properties here>)
new_user.save()
You could also use the bulk_create method to speed things up.
I got tired of struggling with South so I actually ended up doing this differently and it worked out nicely for my particular situation:
First, I made it work with ./manage.py dumpdata, fixing up the dump, and then ./manage.py loaddata, which worked. Then I realized I could do basically the same thing with a single, self-contained script that only loads necessary django settings and does the serialization/deserialization directly.
Self-contained python script
## userconverter.py ##
import json
from django.conf import settings
settings.configure(
DATABASES={
# copy DATABASES configuration from your settings file here, or import it directly from your settings file (but not from django.conf.settings) or use dj_database_url
},
SITE_ID = 1, # because my custom user implicates contrib.sites (which is why it's in INSTALLED_APPS too)
INSTALLED_APPS = ['django.contrib.sites', 'django.contrib.auth', 'myapp'])
# some things you have to import after you configure the settings
from django.core import serializers
from django.contrib.auth.models import User
# this isn't optimized for huge amounts of data -- use streaming techniques rather than loads/dumps if that is your case
old_users = json.loads(serializers.serialize('json', User.objects.all()))
for user in old_users:
user['pk'] = None
user['model'] = "myapp.siteuser"
user['fields']["site"] = settings['SITE_ID']
for new_user in serializers.deserialize('json', json.dumps(old_users)):
new_user.save()
With dumpdata/loaddata
I did the following:
1) ./manage.py dumpdata auth.User
2) Script to convert auth.user data to new user. (or just manually search and replace in your favorite text editor or grep) Mine looked something like:
def convert_user_dump(filename, site_id):
file = open(filename, 'r')
contents = file.read()
file.close()
user_list = json.loads(contents)
for user in user_list:
user['pk'] = None # it will auto-increment
user['model'] = "myapp.siteuser"
user['fields']["site"] = side_id
contents = json.dumps(user_list)
file = open(filename, 'w')
file.write(contents)
file.close()
3) ./manage.py loaddata filename
4) set AUTH_USER_MODEL
*Side Note: One critical part of doing this type of migration, regardless of which technique you use (South, serialization/modification/deserialization, or otherwise) is that as soon as you set AUTH_USER_MODEL to your custom model in the current settings, django cuts you off from auth.User, even if the table still exists.*
We decided to switch to a custom user model in our Django 1.6/Django-CMS 3 project, perhaps a little bit late because we had data in our database that we didn't want to lose (some CMS pages, etc).
After we switched AUTH_USER_MODEL to our custom model, we had a lot of problems that we hadn't anticipated, because a lot of other tables had foreign keys to the old auth_user table, which wasn't deleted. So although things appeared to work on the surface, a lot of things broke underneath: publishing pages, adding images to pages, adding users, etc. because they tried to create an entry in a table that still had a foreign key to auth_user, without actually inserting a matching record into auth_user.
We found a quick and dirty way to rebuild all the tables and relations, and copy our old data across (except for users):
do a full backup of your database with mysqldump
do another backup with no CREATE TABLE statements, and excluding a few tables that won't exist after the rebuild, or will be populated by syncdb --migrate on a fresh database:
south_migrationhistory
auth_user
auth_user_groups
auth_user_user_permissions
auth_permission
django_content_types
django_site
any other tables that belong to apps that you removed from your project (you might only find this out by experimenting)
drop the database
recreate the database (e.g. manage.py syncdb --migrate)
create a dump of the empty database (to make it faster to go round this loop again)
attempt to load the data dump that you created above
if it fails to load because of a duplicate primary key or a missing table, then:
edit the dump with a text editor
remove the statements that lock, dump and unlock that table
reload the empty database dump
try to load the data dump again
repeat until the data dump loads without errors
The commands that we ran (for MySQL) were:
mysqldump <database> > ~/full-backup.sql
mysqldump <database> \
--no-create-info \
--ignore-table=<database>.south_migrationhistory \
--ignore-table=<database>.auth_user \
--ignore-table=<database>.auth_user_groups \
--ignore-table=<database>.auth_user_user_permissions \
--ignore-table=<database>.auth_permission \
--ignore-table=<database>.django_content_types \
--ignore-table=<database>.django_site \
> ~/data-backup.sql
./manage.py sqlclear
./manage.py syncdb --migrate
mysqldump <database> > ~/empty-database.sql
./manage.py dbshell < ~/data-backup.sql
(edit ~/data-backup.sql to remove data dumped from a table that no longer exists)
./manage.py dbshell < ~/empty-database.sql
./manage.py dbshell < ~/data-backup.sql
(repeat until clean)
In django models we have option named managed which can be set True or False
According to documentation the only difference this option makes is whether table will be managed by django or not. Is management by django or by us makes any difference?
Is there any pros and cons of using one option rather than other?
I mean why would we opt for managed=False? Will it give some extra control or power which affects my code?
The main reason for using managed=False is if your model is backed by something like a database view, instead of a table - so you don't want Django to issue CREATE TABLE commands when you run syncdb.
Right from Django docs:
managed=False is useful if the model represents an existing table or a database view that has been created by some other means. This is the only difference when managed=False. All other aspects of model handling are exactly the same as normal
When ever we create the django model, the managed=True implicitly is
true by default. As we know that when we run python manage.py makemigrations the migration file(which we can say a db view) is
created in migration folder of the app and to apply that migration i.e
creates the table in db or we can say schema.
So by managed=False, we restrict Django to create table(scheme, update
the schema of the table) of that model or its fields specified in
migration file.
Why we use its?
case1: Sometime we use two db for the project for
example we have db1(default) and db2, so we don't want particular
model to be create the schema or table in db1 so we can this or we can
customize the db view.
case2. In django ORM, the db table is tied to django ORM model, It
help tie a database view to bind with a django ORM model.
Can also go through the link:
We can add our raw sql for db view in migration file.
The raw sql in migration look like: In 0001_initial.py
from future import unicode_literals
from django.db import migrations, models
class Migration(migrations.Migration):
initial = True
dependencies = [
]
operations = [
migrations.RunSQL(
CREATE OR REPLACE VIEW app_test AS
SELECT row_number() OVER () as id,
ci.user_id,
ci.company_id,
),
]
Above code is just for overview of the looking of the migration file, can go through above link for brief.