I am trying to add indexes on model fields using Field.db_index for an app that has migrations. Looking at Django's documentation all I need to do is to set db_index=True:
class Person(models.Model):
first_name = models.CharField()
last_name = models.CharField(db_index=True)
and then I first tried the new Django's Migration:
./manage.py makemigrations app-name
but Migration does not seem to notice the change and does not add the sql command for creating an index. So I tried django-admin.py as explained here:
django-admin.py sqlindexes app-name
But that does not print the sql command either and it exits with the following error:
CommandError: App 'app-name' has migrations. Only the sqlmigrate and sqlflush commands can be used when an app has migrations.
This problem still exists in django2.1.
I solved it by using the indexes Meta option. This is a bit cleaner than the index_together solution.
class Person(models.Model):
first_name = models.CharField()
last_name = models.CharField()
class Meta:
indexes = [
models.Index(fields=['last_name']),
]
OK, I managed to create the indexes using Meta.index_together. It is not the cleanest way, since I am not actually indexing multiple fields together but it works with makemigrations:
class Person(models.Model):
class Meta():
index_together = [['last_name']]
first_name = models.CharField()
last_name = models.CharField()
Now makemigrations does make a new migration:
./manage.py makemigrations app-name
>>Migrations for 'app-name':
>> 0005_auto_20140929_1540.py:
>> - Alter index_together for Person (1 constraint(s))
And the corresponding sql command is actually CREATE INDEX.
./manage.py sqlmigrate app-name 0005_auto_20140929_1540
>>BEGIN;
>>CREATE INDEX app-name_person_last_name_7...4_idx ON `app-name_person` (`last_name`);
>>COMMIT;
You can do this explicitly in your migration using Django's AddIndex and Index classes.
First create an empty migration with manage.py makemigrations --empty and then simply fill it out as follows:
from django.db import migrations
from django.db.models.indexes import Index
from django.db.migrations import AddIndex
class Migration(migrations.Migration):
dependencies = [
('app_name', 'ref_to_previous_migration'),
]
operations = [
AddIndex('ModelName', Index(fields=['field_name'], name='my_index'))
]
You can use options on the Index class to specify fields, add a name, and do special custom things like index only part of the table, etc. Check the doc links above.
Related
So I changed the names and added a column to a model in django.
Before:
class MyApp(models.Model):
id = models.AutoField(primary_key=True)
aaa = models.CharField(max_length=100)
bbb = models.CharField(max_length=100)
After:
class MyApp(models.Model):
id = models.AutoField(primary_key=True)
first = models.CharField(max_length=100)
second = models.CharField(max_length=100)
third = models.CharField(max_length=100)
I made these changes in the MyApp's view, model, and serializer, however when I try to access my new API endpoint, it fails because the database doesn't contain the new column names. How can I update the database to reflect my new model? (I don't care about any of the data for this model, so I can wipe it). No idea how to do this
Make sure you run the commands
python manage.py makemigrations appname
python manage.py migrate appname
If you get table already exists run command
python manage.py migrate --fake appname
This solved the problem when I had it.
https://docs.djangoproject.com/en/1.11/topics/migrations/#initial-migrations
I need to change the type of a field in one of my Django models from CharField to ForeignKey. The fields are already populated with data, so I was wondering what is the best or right way to do this. Can I just update the field type and migrate, or are there any possible 'gotchas' to be aware of? N.B.: I just use vanilla Django management operations (makemigrations and migrate), not South.
This is likely a case where you want to do a multi-stage migration. My recommendation for this would look something like the following.
First off, let's assume this is your initial model, inside an application called discography:
from django.db import models
class Album(models.Model):
name = models.CharField(max_length=255)
artist = models.CharField(max_length=255)
Now, you realize that you want to use a ForeignKey for the artist instead. Well, as mentioned, this is not just a simple process for this. It has to be done in several steps.
Step 1, add a new field for the ForeignKey, making sure to mark it as null:
from django.db import models
class Album(models.Model):
name = models.CharField(max_length=255)
artist = models.CharField(max_length=255)
artist_link = models.ForeignKey('Artist', null=True)
class Artist(models.Model):
name = models.CharField(max_length=255)
...and create a migration for this change.
./manage.py makemigrations discography
Step 2, populate your new field. In order to do this, you have to create an empty migration.
./manage.py makemigrations --empty --name transfer_artists discography
Once you have this empty migration, you want to add a single RunPython operation to it in order to link your records. In this case, it could look something like this:
def link_artists(apps, schema_editor):
Album = apps.get_model('discography', 'Album')
Artist = apps.get_model('discography', 'Artist')
for album in Album.objects.all():
artist, created = Artist.objects.get_or_create(name=album.artist)
album.artist_link = artist
album.save()
Now that your data is transferred to the new field, you could actually be done and leave everything as is, using the new field for everything. Or, if you want to do a bit of cleanup, you want to create two more migrations.
For your first migration, you will want to delete your original field, artist. For your second migration, rename the new field artist_link to artist.
This is done in multiple steps to ensure that Django recognizes the operations properly. You could create a migration manually to handle this, but I will leave that to you to figure out.
Adding on top of Joey's answer, detailed steps for Django 2.2.11.
Here are the models from my use case, that consists of a Company and Employee model. We have to convert designation to a foreign key field. The app name is called core
class Company(CommonFields):
name = models.CharField(max_length=255, blank=True, null=True
class Employee(CommonFields):
company = models.ForeignKey("Company", on_delete=models.CASCADE, blank=True, null=True)
designation = models.CharField(max_length=100, blank=True, null=True)
Step 1
Create a foreign key designation_link in Employee and mark it as null=True
class Designation(CommonFields):
name = models.CharField(max_length=255)
company = models.ForeignKey("Company", on_delete=models.CASCADE, blank=True, null=True)
class Employee(CommonFields):
company = models.ForeignKey("Company", on_delete=models.CASCADE, blank=True, null=True)
designation = models.CharField(max_length=100, blank=True, null=True)
designation_link = models.ForeignKey("Designation", on_delete=models.CASCADE, blank=True, null=True)
Step 2
Create empty migration. Using the command:
python app_code/manage.py makemigrations --empty --name transfer_designations core
This will create a following file in migrations directory.
# Generated by Django 2.2.11 on 2020-04-02 05:56
from django.db import migrations
class Migration(migrations.Migration):
dependencies = [
('core', '0006_auto_20200402_1119'),
]
operations = [
]
Step 3
Populate the empty migration with a function that loops over all Employees, creates a Designation and links it to the Employee.
In my use case each Designation is also linked to a Company. Which means that Designation may contain two rows for "managers", one for company A, another for company B.
Final migration would look something like this:
# core/migrations/0007_transfer_designations.py
# Generated by Django 2.2.11 on 2020-04-02 05:56
from django.db import migrations
def link_designation(apps, schema_editor):
Employee = apps.get_model('core', 'Employee')
Designation = apps.get_model('core', 'Designation')
for emp in Employee.objects.all():
if(emp.designation is not None and emp.company is not None):
desig, created = Designation.objects.get_or_create(name=emp.designation, company=emp.company)
emp.designation_link = desig
emp.save()
class Migration(migrations.Migration):
dependencies = [
('core', '0006_auto_20200402_1119'),
]
operations = [
migrations.RunPython(link_designation),
]
Step 4
Finally run this migration using:
python app_code/manage.py migrate core 0007
That's a continuation of the great answer by Joey.
How to rename the new field to the original name?
If the field has data, it probably means that you are using it elsewhere in your project, therefore this solution will leave you with a field named differently, and you have to either refactor the project to use the new field or delete the old field and rename the new one.
Be aware that this process is not going to prevent you to refactor code. If you where using a CharField with CHOICES, you were accessing its content with get_filename_display(), for example.
If you try to delete the field to make a migration, for then renaming the other field and make another migration, you'll see Django complaining because you cannot delete a field that you are using in the project.
Just create an empty migration as Joey explained, and put this in operations:
operations = [
migrations.RemoveField(
model_name='app_name',
name='old_field_name',
),
migrations.RenameField(
model_name='app_name',
old_name='old_field_name_link',
new_name='old_field_name',
),
]
Then run migrate and you'll have the changes made in your database, but obviously not in your model, it's time now to delete the old field and to rename new ForeignKey field to the original name.
I don't think that doing this is particularly hacky, but still, only do this kind of things if you are fully understanding what are you messing with.
I have following models
class VucutBolgesi(models.Model):
site = models.ForeignKey(Site)
bolge = models.CharField(verbose_name="Bölge", max_length=75)
hareketler = models.ManyToManyField("Hareket", verbose_name="Hareketler", null=True, blank=True, help_text="Bölgeyi çalıştıran hareketler")
class Hareket(models.Model):
site = models.ForeignKey(Site)
hareket = models.CharField(verbose_name="Hareket", max_length=75 )
bolgeler = models.ManyToManyField(VucutBolgesi, verbose_name="Çalıştırdığı Bölgeler", null=True, blank=True,
help_text="Hareketin çalıştırdığı bölgeler")
I have the same M2M on both table since I wish to display same intermediate table on both admin forms. They also have to use the same table (not create two separate tables) since one change in one admin form must be reflected to the other. Like, If I add a new Hareket to VucutBolgesi through HareketAdmin then the same result shoudl be visible on VucutBolgesiAdmin too.
For achieving this, I first remove hareketler M2M field from VucutBolgesi so Hareketler model would create the intermediate table. I migrate this and then add hareketler to VucutBolgesi with db_table attribute so it will recognize the same intermediary table.
final look of the field is as folows
hareketler = models.ManyToManyField("Hareket", verbose_name="Hareketler", db_table="antrenman_hareket_bolgeler",
null=True, blank=True, help_text="Bölgeyi çalıştıran hareketler")
When I try to migrate this, django throw following exception
django.db.utils.OperationalError: table "antrenman_hareket_bolgeler" already exists
How should I fake this migration?
Following is the migration django creates each time I run makemigrations
dependencies = [
('antrenman', '0005_vucutbolgesi_hareketler'),
]
operations = [
migrations.AddField(
model_name='vucutbolgesi',
name='hareketler',
field=models.ManyToManyField(to='antrenman.Hareket', db_table=b'antrenman_hareket_bolgeler', blank=True, help_text=b'B\xc3\xb6lgeyi \xc3\xa7al\xc4\xb1\xc5\x9ft\xc4\xb1ran hareketler', null=True, verbose_name=b'Hareketler'),
preserve_default=True,
),
]
Note: Editing related migration file and removing migrations.AddField fo not work since django creates the same migrations.AddField with each makemigrations
Is it possible to make a migration always to be faked, just override the apply and unapply methods. The consequences of this are not sufficiently investigated, but this far it works for me.
In the following example we create a migration that reuses django.contrib.auth.User.group's M2M table b'profile_user_groups:
from __future__ import unicode_literals
from django.db import migrations, models
class Migration(migrations.Migration):
dependencies = [
('profile', '0001_initial'),
]
operations = [
migrations.AddField(
model_name='user',
name='organizations',
field=models.ManyToManyField(db_column=b'group_id', db_table=b'profile_user_groups', related_name='members', to='profile.Organization'),
),
]
def apply(self, project_state, schema_editor, collect_sql=False):
return project_state.clone()
def unapply(self, project_state, schema_editor, collect_sql=False):
return project_state.clone()
Solution was so simple.
You must be sure related migration is the only migration operation that needed to be faked. You must first create the migration with
python manage.py makemigrations antrenman
Then apply that migration with --fake
python manage.py migrate --fake antrenman
Handicap is, other developers should know that they have to fake related migration. If there are others migrations alongside with this one, they should make them first and then fake this one.
It is too bad there is no parameter that tells related migration should be real or fake.
I'm trying to modify a M2M field to a ForeignKey field. The command validate shows me no issues and when I run syncdb :
ValueError: Cannot alter field xxx into yyy they are not compatible types (you cannot alter to or from M2M fields, or add or remove through= on M2M fields)
So I can't make the migration.
class InstituteStaff(Person):
user = models.OneToOneField(User, blank=True, null=True)
investigation_area = models.ManyToManyField(InvestigationArea, blank=True,)
investigation_group = models.ManyToManyField(InvestigationGroup, blank=True)
council_group = models.ForeignKey(CouncilGroup, null=True, blank=True)
#profiles = models.ManyToManyField(Profiles, null = True, blank = True)
profiles = models.ForeignKey(Profiles, null = True, blank = True)
Any suggestions?
I stumbled upon this and although I didn't care about my data much, I still didn't want to delete the whole DB. So I opened the migration file and changed the AlterField() command to a RemoveField() and an AddField() command that worked well. I lost my data on the specific field, but nothing else.
I.e.
migrations.AlterField(
model_name='player',
name='teams',
field=models.ManyToManyField(related_name='players', through='players.TeamPlayer', to='players.Team'),
),
to
migrations.RemoveField(
model_name='player',
name='teams',
),
migrations.AddField(
model_name='player',
name='teams',
field=models.ManyToManyField(related_name='players', through='players.TeamPlayer', to='players.Team'),
),
NO DATA LOSS EXAMPLE
I would say: If machine cannot do something for us, then let's help it!
Because the problem that OP put here can have multiple mutations, I will try to explain how to struggle with that kind of problem in a simple way.
Let's assume we have a model (in the app called users) like this:
from django.db import models
class Person(models.Model):
name = models.CharField(max_length=128)
def __str__(self):
return self.name
class Group(models.Model):
name = models.CharField(max_length=128)
members = models.ManyToManyField(Person)
def __str__(self):
return self.name
but after some while we need to add a date of a member join. So we want this:
class Group(models.Model):
name = models.CharField(max_length=128)
members = models.ManyToManyField(Person, through='Membership') # <-- through model
def __str__(self):
return self.name
# and through Model itself
class Membership(models.Model):
person = models.ForeignKey(Person, on_delete=models.CASCADE)
group = models.ForeignKey(Group, on_delete=models.CASCADE)
date_joined = models.DateField()
Now, normally you will hit the same problem as OP wrote. To solve it, follow these steps:
start from this point:
from django.db import models
class Person(models.Model):
name = models.CharField(max_length=128)
def __str__(self):
return self.name
class Group(models.Model):
name = models.CharField(max_length=128)
members = models.ManyToManyField(Person)
def __str__(self):
return self.name
create through model and run python manage.py makemigrations (but don't put through property in the Group.members field yet):
from django.db import models
class Person(models.Model):
name = models.CharField(max_length=128)
def __str__(self):
return self.name
class Group(models.Model):
name = models.CharField(max_length=128)
members = models.ManyToManyField(Person) # <-- no through property yet!
def __str__(self):
return self.name
class Membership(models.Model): # <--- through model
person = models.ForeignKey(Person, on_delete=models.CASCADE)
group = models.ForeignKey(Group, on_delete=models.CASCADE)
date_joined = models.DateField()
create an empty migration using python manage.py makemigrations users --empty command and create conversion script in python (more about the python migrations here) which creates new relations (Membership) for an old field (Group.members). It could look like this:
# Generated by Django A.B on YYYY-MM-DD HH:MM
import datetime
from django.db import migrations
def create_through_relations(apps, schema_editor):
Group = apps.get_model('users', 'Group')
Membership = apps.get_model('users', 'Membership')
for group in Group.objects.all():
for member in group.members.all():
Membership(
person=member,
group=group,
date_joined=datetime.date.today()
).save()
class Migration(migrations.Migration):
dependencies = [
('myapp', '0005_create_models'),
]
operations = [
migrations.RunPython(create_through_relations, reverse_code=migrations.RunPython.noop),
]
remove members field in the Group model and run python manage.py makemigrations, so our Group will look like this:
class Group(models.Model):
name = models.CharField(max_length=128)
add members field the the Group model, but now with through property and run python manage.py makemigrations:
class Group(models.Model):
name = models.CharField(max_length=128)
members = models.ManyToManyField(Person, through='Membership')
and that's it!
Now you need to change creation of members in a new way in your code - by through model. More about here.
You can also optionally tidy it up, by squashing these migrations.
Potential workarounds:
Create a new field with the ForeignKey relationship called profiles1 and DO NOT modify profiles. Make and run the migration. You might need a related_name parameter to prevent conflicts. Do a subsequent migration that drops the original field. Then do another migration that renames profiles1 back to profiles. Obviously, you won't have data in the new ForeignKey field.
Write a custom migration: https://docs.djangoproject.com/en/1.7/ref/migration-operations/
You might want to use makemigration and migration rather than syncdb.
Does your InstituteStaff have data that you want to retain?
If you're still developing the application, and don't need to preserve your existing data, you can get around this issue by doing the following:
Delete and re-create the db.
go to your project/app/migrations folder
Delete everything in that folder with the exception of the init.py file. Make sure you also delete the pycache dir.
Run syncdb, makemigrations, and migrate.
Another approach that worked for me:
Delete the existing M2M field and run migrations.
Add the FK field and run migrations again.
FK field added in this case has no relation to the previously used M2M field and hence should not create any problems.
This link helps you resolve all problems related to this
The one which worked for me is python3 backend/manage.py migrate --fake "app_name"
I literally had the same error for days and i had tried everything i saw here but still didn'y work.
This is what worked for me:
I deleted all the files in migrations folder exceps init.py
I also deleted my database in my case it was the preinstalled db.sqlite3
After this, i wrote my models from the scratch, although i didn't change anything but i did write it again.
Apply migrations then on the models and this time it worked and no errors.
This worked for Me as well
Delete last migrations
run command python manage.py migrate --fake <application name>
run command 'python manage.py makemigrations '
run command 'python manage.py migrate'
Hope this will solve your problem with deleting database/migrations
First delete the migrations in your app (the folders/ files under 'migrations'
folder)
Showing the 'migrations' folder
Then delete the 'db.sqlite3' file
Showing the 'db.sqlite3' file
And run python manage.py makemigrations name_of_app
Finally run python manage.py migrate
I had the same problem and found this How to Migrate a ‘through’ to a many to many relation in Django article which is really really helped me to solve this problem. Please have a look. I'll summarize his answer here,
There is three model and one(CollectionProduct) is going to connect as many-to-many relationship.
This is the final output,
class Product(models.Model):
pass
class Collection(models.Model):
products = models.ManyToManyField(
Product,
blank=True,
related_name="collections",
through="CollectionProduct",
through_fields=["collection", "product"],
)
class CollectionProduct(models.Model):
collection = models.ForeignKey(Collection, on_delete=models.CASCADE)
product = models.ForeignKey(Product, on_delete=models.CASCADE)
class Meta:
db_table = "product_collection_products"
and here is the solution,
The solution
Take your app label (the package name, e.g. ‘product’) and your M2M field name, and combine them together with and underscore:
APPLABEL + _ + M2M TABLE NAME + _ + M2M FIELD NAME
For example in our case, it’s this:
product_collection_products
This is your M2M’s through database table name. Now you need to edit your M2M’s through model to this:
Also found another solution in In Django you cannot add or remove through= on M2M fields article which is going to edit migration files. I didn't try this, but have a look if you don't have any other solution.
this happens when adding 'through' attribute to an existing M2M field:
as M2M fields are by default handled by model they are defined in (if through is set).
although when through is set to new model the M2M field is handled by that new model, hence the error in alter
solutions:-
you can reset db or
remove those m2m fields and run migration as explained above then create them again
*IF YOU ARE IN THE INITIAL STAGES OF DEVELOPMENT AND CAN AFFORD TO LOOSE DATA :)
delete all the migration files except init.py
then apply the migrations.
python manage.py makemigrations
python manage.py migrate
this will create new tables.
In django model I had a class named Invitation.
I execute manage.py syncdb table Invitation is created.
This is my first table.
But when i create another class named Image and execute manage.py syncdb
it returns an error.
that Table UserInvitation already exists.
Please help me to create the table Image using syncdb command.
Models
class UserInvitation(models.Model):
InvitationID = models.AutoField(primary_key=True)
InvitationCode = models.CharField(max_length=255)
Email = models.CharField(max_length=150)
ExpireDate = models.DateTimeField()
Deleted = models.BooleanField(default=False)
CreatedDate = models.DateTimeField(auto_now=True)
class Meta:
db_table = u'UserInvitation'
class UserImage(models.Model):
ImageID = models.AutoField(primary_key=True)
UserID = models.IntegerField(unique=True)
FileName = models.CharField(max_length=255)
class Meta:
db_table = u'UserImage'
You should use South to reflect changes in your database.
syncdb runs commands that create all the tables in the DB, not just the one that you've added.
With South, you should revert your model back to when it only had the UserInvitation class, run the command:
python manage.py convert_to_south <name of app>
Add back the UserImage class and run the command:
python manage.py schemamigration --auto <name of app>
python manage.py migrate <name of app>
This would add the userimage table in your database.
Also, the db_table field in the meta classes should be in lowercase, as the table names, when created, are in lowercase (check your db to make sure)
See South documentation: http://south.readthedocs.org/en/latest/