I'm using the contribute_to_class method but I don't know how to create the field in the database with new migrations.
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83
要回答您的问题，使用Django 1.7中引入的新迁移，为了向模型添加新字段，您只需将该字段添加到您的模型并初始化迁移，./manage.py makemigrations然后运行./manage.py migrate，新字段将添加到您的数据库.
但是，为了避免处理现有模型的错误，您可以使用--fake：
为现有模型初始化迁移：
./manage.py makemigrations myapp现有模型的虚假迁移：
./manage.py migrate --fake myapp将新字段添加到 myapp.models：
from django.db import models class MyModel(models.Model): ... #existing fields newfield = models.CharField(max_length=100) #new field再次运行 makemigrations（这将在迁移文件夹中添加一个新的迁移文件，将新字段添加到 db）：
./manage.py makemigrations myapp再次运行迁移：
./manage.py migrate myapp
于 2014-08-12T21:00:49.700 回答
6
为了能够做到这一点并将迁移文件放在我实际添加字段的应用程序中，而不是将迁移放在模型所属的应用程序中，我必须编写自己的 Migration 基类。
如果您contribute_to_class在与原始模型相同的应用程序中使用，@nima 的答案非常有效，尽管我不明白使用的意义contribute_to_class。
这是代码。self.migrated_app它是 Django 的原始代码，适用于从而不是迁移模型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
使用位于base.utils手写迁移中的这个新迁移类将如下所示。您还可以让 Django 在“错误”应用程序中为您编写迁移，移动文件并更新它以使用自定义迁移类：
# -*- 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,
),
]
Django 1.8 的自定义迁移类
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
于 2014-12-12T19:14:14.273 回答
4
你可以这样创建：
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)
有关更多信息，请参阅“ Django 模型字段注入”。
于 2014-06-19T16:52:25.697 回答
0
您好，如果要更改现有模型，您可以将字段添加到模型中，如果数据可用于同一数据库表，请确保该字段允许空白
Django==3.2.5
我的型号代码
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)
我添加了 new image = models.ImageField(blank=True) 模型表数据在该表上可用，因此需要 (blank=True)
page_home 是我的 django 应用程序名称（你已经给你的应用程序名称）
$ python manage.py migrate
**迁移完成**
于 2021-07-14T04:14:00.097 回答