I am building a Blog App and I am trying to add inbuilt initial instances in django admin so when user clone the repo , then user will see several initial blogs every time even after reset the database.
I didn't find anywhere to set the initial data. I also tried How to set initial data for Django admin model add instance form? But it was not what i am trying to do.
models.py
class BlogPost(models.Model):
title = models.CharField(max_length=1000)
body = models.CharField(max_length=1000)
I tried to use Providing data with fixtures But I have no idea , How can I store in.
Any help would be much Appreciated. Thank You.
Fixtures still need to be loaded manually. You can add that step into installation instruction, something like "to load example data, install the provided fixture via manage.py loaddata ./my_blog_fixture.json
If you want to have the data inserted into database without any user's action, then you are looking for a Data Migration
that's a kind of database migration which does not change the database structure in any way, but it executes a custom command, eg. inserting some data. An example (adjustments needed to match your app name) below. You can either generate an empty migration (recommended) or append RunCommand into an existing migration.
To generate a new empty migration run makemigrations
$ manage.py makemigrations your_app_name --empty
then edit the migration and add RunPython there (see linked docs above).
from django.db import migrations
def insert_blogpost(apps, schema_editor):
BlogPost = apps.get_model('your_app_name', 'BlogPost')
post = BlogPost(title="hello", body="post content")
post.save()
class Migration(migrations.Migration):
dependencies = [
('your_app_name', '0001_initial'),
]
operations = [
migrations.RunPython(insert_blogpost),
]
I have an application in Django 2.0 and as a database engine I use MySQL. I have a problem because the database was previously created and already has records, my idea is to use this same database for the application I am creating.
Use the command
python manage.py inspectdb > models.py
To create the models.py file which will be cleaned as indicated by the models.py file that was generated.
#This is an auto-generated Django model module.
# You'll have to do the following manually to clean this up:
# * Rearrange models' order
# * Make sure each model has one field with primary_key=True
# * Make sure each ForeignKey has `on_delete` set to the desired behavior.
# * Remove `managed = False` lines if you wish to allow Django to create, modify, and delete the table
# Feel free to rename the models, but don't rename db_table values or field names.
After this I proceed to execute:
python manage.py migrate
python manage.py makemigrations
python manage.py migrate
But it generates the following error:
(1050, "Table 'XXXXXXX' already exists")
Obviously it tells me that the table already exists, but how do I not generate this error and continue administering the tables from Django.
You need to run --fake-initial or --fake. See more at Django migrations. Be careful because running inspectdb doesn't solve all your problems. You need to fix the things inside models.py manually and migrate again.
One of the things (and the main reason I do not use Django) is it likes to take control of everything. The fact that it controls the database means that if you don't start strictly in Django, you are doing it wrong.
However there is a work around:
https://docs.djangoproject.com/en/2.0/howto/legacy-databases/
I've made a migration that added a new table and want to revert it and delete the migration, without creating a new migration.
How do I do it? Is there a command to revert last migration and then I can simply delete the migration file?
You can revert by migrating to the previous migration.
For example, if your last two migrations are:
0010_previous_migration
0011_migration_to_revert
Then you would do:
./manage.py migrate my_app 0010_previous_migration
You don't actually need to use the full migration name, the number is enough, i.e.
./manage.py migrate my_app 0010
You can then delete migration 0011_migration_to_revert.
If you're using Django 1.8+, you can show the names of all the migrations with
./manage.py showmigrations my_app
To reverse all migrations for an app, you can run:
./manage.py migrate my_app zero
The answer by Alasdair covers the basics
Identify the migrations you want by ./manage.py showmigrations
migrate using the app name and the migration name
But it should be pointed out that not all migrations can be reversed. This happens if Django doesn't have a rule to do the reversal. For most changes that you automatically made migrations by ./manage.py makemigrations, the reversal will be possible. However, custom scripts will need to have both a forward and reverse written, as described in the example here:
https://docs.djangoproject.com/en/1.9/ref/migration-operations/
How to do a no-op reversal
If you had a RunPython operation, then maybe you just want to back out the migration without writing a logically rigorous reversal script. The following quick hack to the example from the docs (above link) allows this, leaving the database in the same state that it was after the migration was applied, even after reversing it.
# -*- coding: utf-8 -*-
from __future__ import unicode_literals
from django.db import migrations, models
def forwards_func(apps, schema_editor):
# We get the model from the versioned app registry;
# if we directly import it, it'll be the wrong version
Country = apps.get_model("myapp", "Country")
db_alias = schema_editor.connection.alias
Country.objects.using(db_alias).bulk_create([
Country(name="USA", code="us"),
Country(name="France", code="fr"),
])
class Migration(migrations.Migration):
dependencies = []
operations = [
migrations.RunPython(forwards_func, lambda apps, schema_editor: None),
]
This works for Django 1.8, 1.9
Update: A better way of writing this would be to replace lambda apps, schema_editor: None with migrations.RunPython.noop in the snippet above. These are both functionally the same thing. (credit to the comments)
Don't delete the migration file until after the reversion. I made this mistake and without the migration file, the database didn't know what things to remove.
python manage.py showmigrations
python manage.py migrate {app name from show migrations} {00##_migration file.py}
If you want to revert all migrations, use zero as the name of the migration:
python manage.py migrate app_name_here zero
Delete the migration file. Once the desired migration is in your models...
python manage.py makemigrations
python manage.py migrate
Here is my solution, since the above solution do not really cover the use-case, when you use RunPython.
You can access the table via the ORM with
from django.db.migrations.recorder import MigrationRecorder
>>> MigrationRecorder.Migration.objects.all()
>>> MigrationRecorder.Migration.objects.latest('id')
Out[5]: <Migration: Migration 0050_auto_20170603_1814 for model>
>>> MigrationRecorder.Migration.objects.latest('id').delete()
Out[4]: (1, {u'migrations.Migration': 1})
So you can query the tables and delete those entries that are relevant for you. This way you can modify in detail. With RynPython migrations you also need to take care of the data that was added/changed/removed. The above example only displays, how you access the table via Djang ORM.
I did this in 1.9.1 (to delete the last or latest migration created):
rm <appname>/migrations/<migration #>*
example: rm myapp/migrations/0011*
logged into database and ran this SQL (postgres in this example)
delete from django_migrations where name like '0011%';
I was then able to create new migrations that started with the migration number that I had just deleted (in this case, 11).
To revert a migration:
python manage.py migrate <APP_NAME> <MIGRATION_NUMBER_PREFIX>
MIGRATION_NUMBER_PREFIX is the number prefix of the migration you want to revert to, for instance 0001 to go to 0001_initial.py migration. then you can delete that migration.
You can use zero as your migration number to revert all migrations of an app.
The other thing that you can do is delete the table created manually.
Along with that, you will have to delete that particular migration file. Also, you will have to delete that particular entry in the django-migrations table(probably the last one in your case) which correlates to that particular migration.
You can revert by migrating to the previous migration.
For example use below command:
./manage.py migrate example_app one_left_to_the_last_migration
then delete last_migration file.
If you are facing trouble while reverting back the migration, and somehow have messed it, you can perform fake migrations.
./manage.py migrate <name> --ignore-ghost-migrations --merge --fake
For django version < 1.7 this will create entry in south_migrationhistory table, you need to delete that entry.
Now you'll be able to revert back the migration easily.
PS: I was stuck for a lot of time and performing fake migration and then reverting back helped me out.
First: find the previous migrations of your app,
python manage.py showmigrations
eg:
bz
[X] 0001_initial
[ ] 0002_bazifff
If you want rollback 0002_bazifff migrations,
python manage.py migrate bz 0001_initial
If you want rollback 0001_initial Or all
python manage.py migrate bz zero
It seems can't rollback 0001 only
This answer is for similar cases if the top answer by Alasdair does not help. (E.g. if the unwanted migration is created soon again with every new migration or if it is in a bigger migration that can not be reverted or the table has been removed manually.)
...delete the migration, without creating a new migration?
TL;DR: You can delete a few last reverted (confused) migrations and make a new one after fixing models. You can also use other methods to configure it to not create a table by migrate command. The last migration must be created so that it match the current models.
Cases why anyone do not want to create a table for a Model that must exist:
A) No such table should exist in no database on no machine and no conditions
When: It is a base model created only for model inheritance of other model.
Solution: Set class Meta: abstract = True
B) The table is created rarely, by something else or manually in a special way.
Solution: Use class Meta: managed = False
The migration is created, but never used, only in tests. Migration file is important, otherwise database tests can't run, starting from reproducible initial state.
C) The table is used only on some machine (e.g. in development).
Solution: Move the model to a new application that is added to INSTALLED_APPS only under special conditions or use a conditional class Meta: managed = some_switch.
D) The project uses multiple databases in settings.DATABASES
Solution: Write a Database router with method allow_migrate in order to differentiate the databases where the table should be created and where not.
The migration is created in all cases A), B), C), D) with Django 1.9+ (and only in cases B, C, D with Django 1.8), but applied to the database only in appropriate cases or maybe never if required so. Migrations have been necessary for running tests since Django 1.8. The complete relevant current state is recorded by migrations even for models with managed=False in Django 1.9+ to be possible to create a ForeignKey between managed/unmanaged models or to can make the model managed=True later. (This question has been written at the time of Django 1.8. Everything here should be valid for versions between 1.8 to the current 2.2.)
If the last migration is (are) not easily revertible then it is possible to cautiously (after database backup) do a fake revert ./manage.py migrate --fake my_app 0010_previous_migration, delete the table manually.
If necessary, create a fixed migration from the fixed model and apply it without changing the database structure ./manage.py migrate --fake my_app 0011_fixed_migration.
there is a good library to use its called djagno-nomad, although not directly related to the question asked, thought of sharing this,
scenario: most of the time when switching to project, we feel like it should revert our changes that we did on this current branch, that's what exactly this library does, checkout below
https://pypi.org/project/django-nomad/
All the other answers work great for rolling back linear migrations. However, when the migration is non-linear i.e has multiple leaf nodes and we wish to rollback only one path, then we can do in following way:
X
/ \
A B [A and B can represent any number of linear migrations.]
\ /
Y (merge migration)
If we need to rollback A,B and Y. Then we can do the way other answer states.
i.e python manage.py migrate app X.
However, if need to only unapply one path i.e, rollback B and Y, perform following steps:
Unapply only Y. By doing python manage.py migrate app B (or A; both works).
Remove the migration files A and Y for time being from the project location.
Now unapply B, by doing python manage.py migrate app X.
Bring the migration files A and Y to the original location. Now, you can safely delete the unapplied migrations B and Y, if you wish to.
The gist is django can only rollback migrations if the files are present in the location. If you do not want to rollback a migration path (i.e A here), remove it from the project location while performing rollback.
More on this. https://stackoverflow.com/a/71231925/8663277
I am just learning Django, I have created a model inside an app Book
from django.db import models
class Book(models.Model):
title = models.CharField(max_length=100)
author = models.CharField(max_length=50)
read = models.CharField(max_length=50)
Now I want to generate it's correspondence SQL sentence with the help of
python manage.py sql books
But it's showing me error
CommandError: App 'Books' has migrations. Only the sqlmigrate and sqlflush commands can be used when an app has migrations.
I have used makemigrartion and migrate command it's showing no migration is remaining.
Can anyone have any idea regarding to this error?
Since there is still a bit of backwards compatibility with django 1.6 and below you can still use the sql commands from django-admin. However, you have to delete the migrations folder first.
To get the create statements you need to remove the migrations folder
rm -rf books/migrations
Then you can run the sql statement
./manage.py sql books
Should give you something like this:
BEGIN;
CREATE TABLE "books_book" (
"id" integer NOT NULL PRIMARY KEY AUTOINCREMENT,
"title" varchar(100) NOT NULL,
"author" varchar(50) NOT NULL,
"read" varchar(50) NOT NULL
)
;
COMMIT;
However if what you are after is the select statements. Add back your migrations folder:
mkdir books/migrations/
Then do your create migrations and migrate commands.
From there open up the shell:
./manage.py shell
In the shell you can create a queryset and print the query:
from books.models import Book
print Book.objects.all().query
With that you should get an output like this:
SELECT "book_book"."id", "book_book"."title", "book_book"."author", "book_book"."read" FROM "book_book"
Those are a couple of ways to get sql back, depending on what you are trying to generate. The great thing about the queryset in the shell is you can make that as complex as possible and do a print of the .query and it gives it to you.
Hmm, interesting. Right now, there are two ways of turning models into SQL. The old syncdb method, which will ultimately be removed, and the new migrations method. The old sql* commands were based on the first method, and won't generally work the same way with the migrations approach. So I think this is a technical limitation (though perhaps it's philosophical as well).
Probably the best way to accomplish this is to first squash your migrations (in most cases this should produce a single migrations file) and then generate the SQL for that new migration with the sqlmigrate command.
Inside the app, there will be a directory for migrations where the django will store your model changes as migrations files.
To see the query you have to use the command python manage.py sqlmigrate {your_app_name;{eg :polls}} {migrations_file_name:{eg:0001_init.py}}
command:
python manage.py sqlmigrate polls 0001
Hope this will help
I was wondering how to automatically update my models.py in a specific app in django. I created a new table in my database through HeidySQL, when i syncdb, i see the table appears in the directory in the command line, but not in models.py . I also tried migrate and make migrations but still not working.
Any idea? Thanks!
The manage.py migrate and makemigrations commands work in the opposite direction that you are describing here. If you want to generate a starter template of your models based on the current layout of the database, you can try using the inspectdb command.
python manage.py inspectdb > temp_models.py
This will generate a starter model for every table in the database. You should review and update the generated models so they make sense with your app. Take special note of lines ending with the comment # This field type is a guess.
Once you are satisfied with the new models, copy them over to the app's models.py file.
Hope that helps!