如何使用新的Django迁移向模型添加新字段？
如何使用新的Django迁移向模型添加新字段？
提问于 2014-06-20 00:43:13
我使用的是contribute_to_class方法，但我不知道如何使用新迁移在数据库中创建该字段。
回答 4
Stack Overflow用户
发布于 2014-08-13 05:00:50
为了回答你的问题，在Django 1.7中引入了新的迁移，为了向模型添加新字段，您可以简单地将该字段添加到模型中，并使用./manage.py makemigrations初始化迁移，然后运行./manage.py migrate，新字段将添加到数据库中。
但是，为了避免处理现有模型的错误，您可以使用--fake
- 初始化现有模型的迁移：
./manage.py makemigrations myapp
- 现有机型的假迁移：
./manage.py迁移--fake myapp
- 在myapp.models中添加新字段：
从现有的导入模型类MyModel(models.Model)：... # django.db field 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newfield添加到数据库)：
./manage.py makemigrations myapp
- 再次运行migrate：
./manage.py迁移myapp
Stack Overflow用户
发布于 2014-12-13 03:14:14
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。
如果您在与原始模型相同的应用程序中使用contribute_to_class，则@nima的答案可以完美地工作，尽管我看不出使用contribute_to_class的意义。
下面是代码。它是Django的原始代码，用于从self.migrated_app而不是self.app_label迁移模型
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有了这个位于base.utils中的新迁移类，一个手写的迁移将如下所示。您还可以让Django在“错误的”应用程序中为您编写迁移，移动文件并更新它，以使用自定义的migration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_stateStack Overflow用户
发布于 2014-06-20 00:52:26
您可以像这样创建：
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 Model Field Injection。
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原文链接：
https://stackoverflow.com/questions/24311993
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