Is there any way in Django to populate the database with multiple records during the migration, or after it, except for the manual method, or restore the backup.
For example:
I have a model with services, which after the creation of the database should already have 3 entries, because it is a binder.
How do I implement this in Django 2.x?
From django documentation on Data migrations
Django can’t automatically generate data migrations for you, as it
does with schema migrations, but it’s not very hard to write them.
Migration files in Django are made up of Operations, and the main
operation you use for data migrations is RunPython.
Example
from django.db import migrations
def combine_names(apps, schema_editor):
# We can't import the Person model directly as it may be a newer
# version than this migration expects. We use the historical version.
Person = apps.get_model('yourappname', 'Person')
for person in Person.objects.all():
person.name = '%s %s' % (person.first_name, person.last_name)
person.save()
class Migration(migrations.Migration):
dependencies = [
('yourappname', '0001_initial'),
]
operations = [
migrations.RunPython(combine_names),
]
Related
I have added a UUID to the following model:
class Post(models.Model):
uuid = models.UUIDField(default=uuid.uuid4, editable=False)
...
But there already are entries in the database that were created without the uuid field.
When I run migrate, it adds the same UUID to all my previous objects.
Is there an easy way of populating the existing objects with a different UUID automatically?
I think the easiest way to fix this is to make a data migration [Django-doc]. You create a new migration file with:
python manage.py makemigrations --empty yourappname
This will create a new file in the migrations/ directory that does nothing. We can alter that migration file with something that looks like:
# Generated by Django 3.2 on 2021-05-01 12:49
from django.db import migrations
from uuid import uuid4
class Migration(migrations.Migration):
def populate_uuid(apps, schema_editor):
Post = apps.get_model('yourappname', 'Post')
posts = list(Post.objects.all())
for post in posts:
post.uuid = uuid4()
Post.objects.bulk_update(posts, ['uuid'])
dependencies = [
('yourappname', 'previous_migrationname'),
]
operations = [
migrations.RunPython(populate_uuid)
]
If you then migrate, it will load all Post objects, provide these each a unique uuid, and then update the items in bulk.
Problem
I have a database in production with users and I'm creating new permissions in some models. Now I need to add these permissions to some users depending on a condition. How should I do this? Should I add code to the migration to check all users and add permissions to them accordingly?
You can create a DataMigration
This allow you to run your regular migrations and then apply some logic (preferablly using a python code) to do some changes in your DB records.
Example:
from django.db import migrations, models
def my_data_migration_code(apps, schema_editor):
my_model = apps.get_model('your_app', 'MyModel')
for instance in my_model.objects.all():
instance.name = instance.name + ' wow'
instance.save()
class Migration(migrations.Migration):
dependencies = [
('your_app', '0050_auto_20190207_1156'),
]
operations = [
migrations.AddField(
model_name='MyModel',
name='blabla',
field=models.BooleanField(default=True),
),
migrations.RunPython(my_data_migration_code)
]
I want my application to have default data such as user types.
What's the most efficient way to manage default data after migrations?
It needs to handle situations such as, after I add a new table, it adds the default data for it.
You need to create an empty migration file and Do your stuff in operations block, as explained in docs.
Data Migrations
As well as changing the database schema, you can also use migrations to change the data in the database itself, in conjunction with the schema if you want.
Now, all you need to do is create a new function and have RunPython use it
Docs explains this with an example to show ,how to communicate with your models.
From Docs
To create an empty migration file,
python manage.py makemigrations --empty yourappname
And this is the example how to update a newly added field.
# -*- coding: utf-8 -*-
from __future__ import unicode_literals
from django.db import migrations, models
def combine_names(apps, schema_editor):
# We can't import the Person model directly as it may be a newer
# version than this migration expects. We use the historical version.
Person = apps.get_model("yourappname", "Person")
for person in Person.objects.all():
person.name = "%s %s" % (person.first_name, person.last_name)
person.save()
class Migration(migrations.Migration):
initial = True
dependencies = [
('yourappname', '0001_initial'),
]
operations = [
migrations.RunPython(combine_names),
]
The accepted answer is fine. But, since OP asked the question in the context of adding new rows and not updating existing entries. Here is the code snippet for adding new entries :
from django.db import migrations
class Migration(migrations.Migration):
dependencies = [
('loginmodule', '0002_login_avatar'),
]
def insertData(apps, schema_editor):
Login = apps.get_model('loginmodule', 'Login')
user = Login(name = "admin", login_id = "admin", password = "password", email = "admin#pychat.com", type = "Admin", avatar="admin.jpg")
user.save()
operations = [
migrations.RunPython(insertData),
]
Update:
most users are looking for data migration as suggested by #durdenk in https://stackoverflow.com/a/39742847/3627387. But what OP was asking is about a way to add data after migrations, that is why this is accepted answer.
Original answer:
I think what you are looking for is fixtures https://docs.djangoproject.com/en/1.10/howto/initial-data/
From docs
It’s sometimes useful to pre-populate your database with hard-coded data when you’re first setting up an app. You can provide initial data via fixtures.
Also read this https://code.djangoproject.com/wiki/Fixtures
Answer is given above just to show how to insert new rows to the table.
from django.db import migrations, models
from yourapp.models import <yourmodel>
def combine_names(apps, schema_editor):
obj = <yourmodel>(arrib=value)
obj.save()
For example let's say you have model Person
person = Person(first_name='raj', last_name='shah')
person.save()
I'm trying to rename a model and I would like to write the migration in the way that it doesn't depend on the old name still present while it being applied. Can I somehow get data from a database table that no longer has a model in my migration code?
Details:
I have a Region model that I want to move into a more generic GeoObject model and remove from the models.py. If I write my migration code that creates GeoObjects from existing Regions with from models import Region I'll have to keep Region model until my main database will migrate. But I'd like to write a migration so that it doesn't depend on Region model being present, just check that the database table exists and use it. Is it possible to do it using Django instruments, without depending on a specific database type if possible?
Yes, you can.
But first of all, you really shouldn't import any model inside migration.
Take look at RunPython operation, that will allow you to run any python code inside your migration. RunPython will pass to your function 2 parameters: apps and schema_editor. First parameter contains structure of your models at stage of applying that migration, so if actual removing of model is later on that migration, you can still access that model using apps passed into function.
Let's say your model looked like this:
class SomeModel(models.Model):
some_field = models.CharField(max_length=32)
Now you're deleting that model, automatically created migration will contain:
class Migration(migrations.Migration):
dependencies = [
('yourapp', '0001_initial'), # or any other dependencies
]
operations = [
migrations.DeleteModel(
name='Main',
),
]
You can modify that migration by injecting RunPython just above DeleteModel operation:
operations = [
migrations.RunPython(
move_data_to_other_model,
move_data_back, # for backwards migration - if you won't ever want to undo this migration, just don't pass that function at all
),
migrations.DeleteModel(
name='SomeModel',
),
]
and creating 2 functions before Migration class:
def move_data_to_other_model(apps, schema_editor):
SomeModel = apps.get_model('yourapp', 'SomeModel')
for something in SomeModel.objects.all():
# do your data migration here
o = OtherModel.objects.get(condition=True)
o.other_field = something.some_field
def move_data_back(apps, schema_editor):
SomeModel = apps.get_model('yourapp', 'SomeModel')
for something in OtherModel.objects.all():
# move back your data here
SomeModel(
some_field=something.other_field,
).save()
It doesn't matter that your model is no longer defined in models.py, django can rebuild that model based on migration history. But remember: save method from your models (and other customized methods) won't be called in migrations. Also any pre_save or post_save signals won't be triggered.
I want to create groups in django programmatically, but not in a view, but rather in something like model (for example using migrations). How to do it? There's no information about it in google and docs (at least not here: https://docs.djangoproject.com/en/1.7/topics/auth/default/#groups)
Okay, it seems you're using Django 1.7's new migrations system. This is similar to but not exactly like South.
A migration that involves altering the data in the tables is a data migration, and you typically need to write Python code to do the migration.
From the Django docs, there's this example:
# -*- coding: utf-8 -*-
from django.db import models, migrations
def combine_names(apps, schema_editor):
# We can't import the Person model directly as it may be a newer
# version than this migration expects. We use the historical version.
Person = apps.get_model("yourappname", "Person")
for person in Person.objects.all():
person.name = "%s %s" % (person.first_name, person.last_name)
person.save()
class Migration(migrations.Migration):
dependencies = [
('yourappname', '0001_initial'),
]
operations = [
migrations.RunPython(combine_names),
]
Note that the code to run during the migration is in the combine_names function, which is called by the migrations.RunPython(combine_names) entry in the operations list of the migration. Your migration should do its group creation in a function like that, along with whatever other data migration is needed.
You should probably use a line like
Group = apps.get_model("auth", "Group")
my_group, created = Group.objects.get_or_create(name='group1')
to create your groups, in case there is already a group of that name in the table.
Don't put code to run during a migration into the root level of the Python file; if you do so, it will be run every time that migration is imported, for example, every time you run ./manage.py runserver.
P.S. You need to put your migrations.RunPython entry at the right point in the operations list; it won't work if you put it after an operation that deletes a table it needs, for example.
Groups are just like any other Django model. You can create them as you would anything else.
my_group = Group.objects.create(name='group1')