91
To answer your question, with the new migration introduced in Django 1.7, in order to add a new field to a model you can simply add that field to your model and initialize migrations with ./manage.py makemigrations and then run ./manage.py migrate and the new field will be added to your DB.
To avoid dealing with errors for your existing models however, you can use the --fake:
-
Initialize migrations for your existing models:
./manage.py makemigrations myapp -
Fake migrations for existing models:
./manage.py migrate --fake myapp -
Add the new field to myapp.models:
from django.db import models class MyModel(models.Model): ... #existing fields newfield = models.CharField(max_length=100) #new field -
Run makemigrations again (this will add a new migration file in migrations folder that add the newfield to db):
./manage.py makemigrations myapp -
Run migrate again:
./manage.py migrate myapp
6
To be able to do that and have the migration file located in the application where I actually add the field as opposed to having the migration located inside the application to which the model belongs, I had to write my own Migration base class.
If you use contribute_to_class inside the same application as the original model, @nima’s answer works perfectly, although I don’t see the point of using contribute_to_class then.
Here is the code. It is Django’s original code adapted to migrate a model from self.migrated_app instead of self.app_label:
from django.db import migrations
class Migration(migrations.Migration):
migrated_app = None
def __init__(self, name, app_label):
super(Migration,self).__init__(name, app_label)
if self.migrated_app is None:
self.migrated_app = self.app_label
def mutate_state(self, project_state):
new_state = project_state.clone()
for operation in self.operations:
operation.state_forwards(self.migrated_app, new_state)
return new_state
def apply(self, project_state, schema_editor, collect_sql=False):
for operation in self.operations:
if collect_sql and not operation.reduces_to_sql:
schema_editor.collected_sql.append("--")
schema_editor.collected_sql.append("-- MIGRATION NOW PERFORMS OPERATION THAT CANNOT BE WRITTEN AS SQL:")
schema_editor.collected_sql.append("-- %s" % operation.describe())
schema_editor.collected_sql.append("--")
continue
new_state = project_state.clone()
operation.state_forwards(self.migrated_app, new_state)
if not schema_editor.connection.features.can_rollback_ddl and operation.atomic:
with atomic(schema_editor.connection.alias):
operation.database_forwards(self.migrated_app, schema_editor, project_state, new_state)
else:
operation.database_forwards(self.migrated_app, schema_editor, project_state, new_state)
project_state = new_state
return project_state
def unapply(self, project_state, schema_editor, collect_sql=False):
to_run = []
for operation in self.operations:
if collect_sql and not operation.reduces_to_sql:
schema_editor.collected_sql.append("--")
schema_editor.collected_sql.append("-- MIGRATION NOW PERFORMS OPERATION THAT CANNOT BE WRITTEN AS SQL:")
schema_editor.collected_sql.append("-- %s" % operation.describe())
schema_editor.collected_sql.append("--")
continue
if not operation.reversible:
raise Migration.IrreversibleError("Operation %s in %s is not reversible" % (operation, self))
new_state = project_state.clone()
operation.state_forwards(self.migrated_app, new_state)
to_run.append((operation, project_state, new_state))
project_state = new_state
to_run.reverse()
for operation, to_state, from_state in to_run:
if not schema_editor.connection.features.can_rollback_ddl and operation.atomic:
with atomic(schema_editor.connection.alias):
operation.database_backwards(self.migrated_app, schema_editor, from_state, to_state)
else:
operation.database_backwards(self.migrated_app, schema_editor, from_state, to_state)
return project_state
With this new Migration class located in base.utils a hand-written migration would look like this. You can also let Django write the migration for you inside the “wrong” application, move the file and update it to use the custom Migration class:
# -*- coding: utf-8 -*-
from __future__ import unicode_literals
from django.db import models, migrations
from base.utils import Migration
import dynamicsites.fields
class Migration(Migration):
dependencies = [
('sites', '0001_initial'),
('base', '0001_initial'),
]
migrated_app = 'sites'
operations = [
migrations.AddField(
model_name='site',
name='folder_name',
field=dynamicsites.fields.FolderNameField(default='', help_text=b"Folder name for this site's files. The name may only consist of lowercase characters, numbers (0-9), and/or underscores", max_length=64, blank=True),
preserve_default=False,
),
migrations.AddField(
model_name='site',
name='subdomains',
field=dynamicsites.fields.SubdomainListField(default=(), help_text=b'Comma separated list of subdomains this site supports. Leave blank to support all subdomains', blank=True),
preserve_default=False,
),
]
Custom migration class for Django 1.8
from django.db import migrations
class Migration(migrations.Migration):
migrated_app = None
def __init__(self, name, app_label):
super(Migration,self).__init__(name, app_label)
if self.migrated_app is None:
self.migrated_app = self.app_label
def __eq__(self, other):
if not isinstance(other, Migration):
if not isinstance(other, migrations.Migration):
return False
return (self.name == other.name) and (self.migrated_app == other.app_label)
return (self.name == other.name) and (self.migrated_app == other.migrated_app)
def __hash__(self):
return hash("%s.%s" % (self.app_label, self.name))
def mutate_state(self, project_state, preserve=True):
new_state = project_state
if preserve:
new_state = project_state.clone()
for operation in self.operations:
operation.state_forwards(self.migrated_app, new_state)
return new_state
def apply(self, project_state, schema_editor, collect_sql=False):
for operation in self.operations:
if collect_sql and not operation.reduces_to_sql:
schema_editor.collected_sql.append("--")
schema_editor.collected_sql.append("-- MIGRATION NOW PERFORMS OPERATION THAT CANNOT BE "
"WRITTEN AS SQL:")
schema_editor.collected_sql.append("-- %s" % operation.describe())
schema_editor.collected_sql.append("--")
continue
old_state = project_state.clone()
operation.state_forwards(self.migrated_app, project_state)
if not schema_editor.connection.features.can_rollback_ddl and operation.atomic:
with atomic(schema_editor.connection.alias):
operation.database_forwards(self.migrated_app, schema_editor, old_state, project_state)
else:
operation.database_forwards(self.migrated_app, schema_editor, old_state, project_state)
return project_state
def unapply(self, project_state, schema_editor, collect_sql=False):
to_run = []
new_state = project_state
for operation in self.operations:
if not operation.reversible:
raise Migration.IrreversibleError("Operation %s in %s is not reversible" % (operation, self))
new_state = new_state.clone()
old_state = new_state.clone()
operation.state_forwards(self.migrated_app, new_state)
to_run.insert(0, (operation, old_state, new_state))
for operation, to_state, from_state in to_run:
if collect_sql:
if not operation.reduces_to_sql:
schema_editor.collected_sql.append("--")
schema_editor.collected_sql.append("-- MIGRATION NOW PERFORMS OPERATION THAT CANNOT BE "
"WRITTEN AS SQL:")
schema_editor.collected_sql.append("-- %s" % operation.describe())
schema_editor.collected_sql.append("--")
continue
if not schema_editor.connection.features.can_rollback_ddl and operation.atomic:
with atomic(schema_editor.connection.alias):
operation.database_backwards(self.migrated_app, schema_editor, from_state, to_state)
else:
operation.database_backwards(self.migrated_app, schema_editor, from_state, to_state)
return project_state
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4
You can create like this:
from django.db.models import CharField
from django.db.models.signals import class_prepared
def add_field(sender, **kwargs):
"""
class_prepared signal handler that checks for the model named
MyModel as the sender, and adds a CharField
to it.
"""
if sender.__name__ == "MyModel":
field = CharField("New field", max_length=100)
field.contribute_to_class(sender, "new_field")
class_prepared.connect(add_field)
See “Django Model Field Injection” for more information.
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0
hollo if want to change existing model you can add the filed into model, make sure that filed are allow blank if the data available for same database table
Django==3.2.5
my model code
from django.db import models
# Create your models here.
from django.db import models
class slider_item(models.Model):
title = models.CharField(max_length=100 ,blank=True)
description = models.TextField(blank=True)
image = models.ImageField(blank=True)
i added new image = models.ImageField(blank=True) that model table data available on that table so need to (blank=True)
page_home is my django app name (you have give your app name)
$ python manage.py migrate
** migration done **
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Source:stackexchange.com