I have one field in my model with like this name = models.CharField(max_length=100, unique=True) but now that table/model have a lot of data and need to change the True to False but without having to drop the table and créate it again, How can I do that?
Generate the new migration using:
python manage.py makemigrations
The above will detect changes to your model and generate a migration class but no execute any sql yet.
To generate/apply the sql to the db:
python manage.py migrate
If you want to see the sql that will be executed before updating the db do this before migrate:
python sqlmigrate {app_label} {migration_module}
EDIT: The above will rename your table with suffix __old, create a new table and insert the data from the old to the new one, and then drop the original table. So not sure if this is what you want..
Another option would be to use plain sql to achieve what you want:
ALTER TABLE table_name DROP CONSTRAINT constraint_name;
But remember, in order keep your migrations updated for new runs, find the migration class that declares your field as unique and change unique=True to unique=False. If any other servers need to be updated you can run the drop constraint command there too so everything is in sync.
Just change the value to False in the model and then makemigrations and migrate. This will update all items in the DB to the new value. This is if you are using the newer version with South and not using syncdb.
Related
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 added a field to one of my models, but in the 'models' folder I have two other python files which have only View models from which I query views in my database. When I run the makemigrations command, the new migrations file that is created includes also adding these view models to my database as tables (which I don't want to). How can I ignore these changes, and only commit the one addition of a field to an actual table on the database.
I think I maybe have to delete the migrations.CreateModel... in the new migrations file and only keep the migrations.addField... , then run the 'migrate' command. I didn't proceed with this because I'm not sure and maybe it will mess up my database in some way.
Thanks in advance to anyone who can help.
when you make a model for database view you must add meta class managed = false and db_table like this:
class MyViewModel(models.Model):
field: models.CharField(max_length=100)
class Meta:
managed = False
db_table = 'database_view_name'
when you write this and run makemigrations a migration generated contains this model but when you run migrate this migration doesnt change anything on database.
you also can create view using migrations in python. see migrations.RunPython for more details
When I use manage.py makemigrations <app> only columns with relations are migrated to pg database.
How to instruct django to migrate new basic non-relational columns, like:
title = models.CharField(max_length=20, null=True)
I'm using django 1.8.2. on Ubuntu
No fields at all are being migrated when you run manage.py makemigrations <app>, as that command only creates a new migration in your <app>/migrations/ directory. It's only when you run manage.py migrate that changes are written to the database.
If you are not getting the expected results, have a look at the newest migration and determine which fields it affects. All fields should be targeted by migrations, not relational fields only. Changing properties like max_length, blank, required etc. should trigger migrations. If they don't it's probably because your changes doesn't require any database schema modification.
If you are still having problems, please post:
Your models prior to model change
Your models after model change
The migration generated by makemigrations
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 have this model
class Vacancy(models.Model):
user = models.ForeignKey(User, null=True, blank=True, default = None)
name = models.CharField(max_length=64)
When in admin i try to creat a vacancy without a user. And it throws an error " club_vacancy.user_id may not be NULL".
Am i doing something wrong?
club_vacancy.user_id may not be NULL
Looks very much like an error from your database, rather than from Django.
It seems most likely that you added null=True after running manage.py syncdb. You'll need to modify your database schema to allow null values in that column.
Aside from South, another option is to use django evolution for schema changes.
http://code.google.com/p/django-evolution/
Install it before making db changes. Then run
python manage.py evolve --hint --execute
Make sure that if you add a new field, you allow nulls (null=True) or else evolve will give you an error message.
you need to reset you database table (since just syncdb does not update fields that are alredy created with null=False)
./manage.py reset your_app
OR if there is some data that you do not want to loose use SQL commands to remove NOT NULL flag