我有 2 个模型用于 2 个不同的数据库：
数据库是手动创建的，但它应该不会改变任何东西。
class LinkModel(models.Model): # in 'urls' database
id = models.AutoField(primary_key=True)
host_id = models.IntegerField()
path = models.CharField(max_length=255)
class Meta:
db_table = 'links'
app_label = 'testapp'
def __unicode__(self):
return self.path
class NewsModel(models.Model): # in default database
id = models.AutoField(primary_key=True)
title = models.CharField(max_length=50)
link = models.ForeignKey(LinkModel)
class Meta:
db_table = 'news'
app_label = 'test'
def __unicode__(self):
return self.title
执行以下代码后会出现错误
newsItem, created = NewsModel.objects.get_or_create( title="test" )
link = LinkModel.objects.using('urls').get( id=1 )
newsItem.link = link # error!
Cannot assign "<LinkModel: />": instance is on database "default", value is on database "urls"
为什么我不能对不同的数据库使用外键和模型？
Django 目前不提供对跨多个数据库的外键或多对多关系的任何支持。如果您使用路由器将模型分区到不同的数据库，则这些模型定义的任何外键和多对多关系都必须位于单个数据库的内部。
同样的麻烦。 foreignKey() 类中的错误。
在 validate() 方法中。
v1.2、v1.3、v1.4rc1 中存在错误
尝试这个补丁来解决它。
*注意：这是 Vitaly Fadeev 答案的延伸
由于希望保持引用完整性，Django 不允许跨多个数据库的外键：https://docs.djangoproject.com/en/dev//topics/db/multi-db/#limitations-of -多个数据库。尽管 99% 的应用程序都希望这样做，但在某些情况下，即使无法确保引用完整性，也能够在 ORM 中创建此类关联会很有帮助。
我创建了一个要点，它使用Vitaly Fadeev提出的解决方案here包装为DjangoForeignKey字段的子类。此解决方案不需要您修改 Django Core 文件，而是在您需要的情况下使用此字段类型。
# app1/models.py
from django.db import models
class ClientModel(models.Model)
name = models.CharField()
class Meta:
app_label = 'app1'
# app2/models.py
from django.db import models
from some_location.related import SpanningForeignKey
class WidgetModel(models.Model):
client = SpanningForeignKey('app1.ClientModel', default=None, null=True,
blank=True, verbose_name='Client')
要点可以在这里找到：https://gist.github.com/gcko/de1383080e9f8fb7d208
复制此处以便于访问：
from django.core import exceptions
from django.db.models.fields.related import ForeignKey
from django.db.utils import ConnectionHandler, ConnectionRouter
connections = ConnectionHandler()
router = ConnectionRouter()
class SpanningForeignKey(ForeignKey):
def validate(self, value, model_instance):
if self.rel.parent_link:
return
# Call the grandparent rather than the parent to skip validation
super(ForeignKey, self).validate(value, model_instance)
if value is None:
return
using = router.db_for_read(self.rel.to, instance=model_instance)
qs = self.rel.to._default_manager.using(using).filter(
**{self.rel.field_name: value}
)
qs = qs.complex_filter(self.get_limit_choices_to())
if not qs.exists():
raise exceptions.ValidationError(
self.error_messages['invalid'],
code='invalid',
params={
'model': self.rel.to._meta.verbose_name, 'pk': value,
'field': self.rel.field_name, 'value': value,
}, # 'pk' is included for backwards compatibility
)
作为替代方案（虽然有点hackish），您可以子类化ForeignKey来检查右侧数据库中是否存在实例：
class CrossDbForeignKey(models.ForeignKey):
def validate(self, value, model_instance):
if self.rel.parent_link:
return
super(models.ForeignKey, self).validate(value, model_instance)
if value is None:
return
# Here is the trick, get db relating to fk, not to root model
using = router.db_for_read(self.rel.to, instance=model_instance)
qs = self.rel.to._default_manager.using(using).filter(
**{self.rel.field_name: value}
)
qs = qs.complex_filter(self.rel.limit_choices_to)
if not qs.exists():
raise exceptions.ValidationError(self.error_messages['invalid'] % {
'model': self.rel.to._meta.verbose_name, 'pk': value})
然后勉强:
class NewsModel(models.Model): # in default database
…
link = models.CrossDbForeignKey(LinkModel)
请注意，它或多或少对应于 Vitaly 提到的补丁，但这种方式不需要修补 django 源代码。
在打破了我的头几天后，我设法在同一家银行获得我的外键！
可以更改表格以在不同的银行寻求外键！
首先，在函数_init_
中添加FIELDS的RECHARGE，都直接（破解）我的表单app.form.py
# -*- coding: utf-8 -*-
from django import forms
import datetime
from app_ti_helpdesk import models as mdp
#classe para formulario de Novo HelpDesk
class FormNewHelpDesk(forms.ModelForm):
class Meta:
model = mdp.TblHelpDesk
fields = (
"problema_alegado",
"cod_direcionacao",
"data_prevista",
"hora_prevista",
"atendimento_relacionado_a",
"status",
"cod_usuario",
)
def __init__(self, *args, **kwargs):
#-------------------------------------
# using remove of kwargs
#-------------------------------------
db = kwargs.pop("using", None)
# CASE use Unique Key`s
self.Meta.model.db = db
super(FormNewHelpDesk, self).__init__(*args,**kwargs)
#-------------------------------------
# recreates the fields manually
from copy import deepcopy
self.fields = deepcopy( forms.fields_for_model( self.Meta.model, self.Meta.fields, using=db ) )
#
#-------------------------------------
#### follows the standard template customization, if necessary
self.fields['problema_alegado'].widget.attrs['rows'] = 3
self.fields['problema_alegado'].widget.attrs['cols'] = 22
self.fields['problema_alegado'].required = True
self.fields['problema_alegado'].error_messages={'required': 'Necessário informar o motivo da solicitação de ajuda!'}
self.fields['data_prevista'].widget.attrs['class'] = 'calendario'
self.fields['data_prevista'].initial = (datetime.timedelta(4)+datetime.datetime.now().date()).strftime("%Y-%m-%d")
self.fields['hora_prevista'].widget.attrs['class'] = 'hora'
self.fields['hora_prevista'].initial =datetime.datetime.now().time().strftime("%H:%M")
self.fields['status'].initial = '0' #aberto
self.fields['status'].widget.attrs['disabled'] = True
self.fields['atendimento_relacionado_a'].initial = '07'
self.fields['cod_direcionacao'].required = True
self.fields['cod_direcionacao'].label = "Direcionado a"
self.fields['cod_direcionacao'].initial = '2'
self.fields['cod_direcionacao'].error_messages={'required': 'Necessário informar para quem é direcionado a ajuda!'}
self.fields['cod_usuario'].widget = forms.HiddenInput()
从视图调用表单
app.view.py
form = forms.FormNewHelpDesk(request.POST or None, using=banco)
现在，DJANGO 源代码发生变化
只有ForeignKey、ManyToManyField和OneToOneField类型的字段可以使用'using'，所以添加了一个IF ...
django.forms.models.py
# line - 133: add using=None
def fields_for_model(model, fields=None, exclude=None, widgets=None, formfield_callback=None, using=None):
# line - 159
if formfield_callback is None:
#----------------------------------------------------
from django.db.models.fields.related import (ForeignKey, ManyToManyField, OneToOneField)
if type(f) in (ForeignKey, ManyToManyField, OneToOneField):
kwargs['using'] = using
formfield = f.formfield(**kwargs)
#----------------------------------------------------
elif not callable(formfield_callback):
raise TypeError('formfield_callback must be a function or callable')
else:
formfield = formfield_callback(f, **kwargs)
更改关注文件
django.db.models.base.py
改变
# line 717
qs = model_class._default_manager.filter(**lookup_kwargs)
对于
# line 717
qs = model_class._default_manager.using(getattr(self, 'db', None)).filter(**lookup_kwargs)
准备好：D