Question

Is that possible to have model with foreign key fields on different databases? example:

class MultiBDModel(models.Model):
    db1_user = models.ForeignKey(User) # here suppose to be foreign key on `db1`
    db2_user = models.ForeignKey(User) # and here on `db2`

也许可以复制用户。应用自定义管理器。哪个返回查询设置为 = db1 。

在 sections. py 中:

DATABASES = {
     default : {
         ENGINE :  django.db.backends.sqlite3 , # Add  postgresql_psycopg2 ,  mysql ,  sqlite3  or  oracle .
         NAME :  db1 ,                      # Or path to database file if using sqlite3.
         USER :   ,                      # Not used with sqlite3.
         PASSWORD :   ,                  # Not used with sqlite3.
         HOST :   ,                      # Set to empty string for localhost. Not used with sqlite3.
         PORT :   ,                      # Set to empty string for default. Not used with sqlite3.
    },

     website : {
         ENGINE :  django.db.backends.sqlite3 , # Add  postgresql_psycopg2 ,  postgresql ,  mysql ,  sqlite3  or  oracle .
         NAME :  db2 ,                      # Or path to database file if using sqlite3.
         USER :   ,                      # Not used with sqlite3.
         PASSWORD :   ,                  # Not used with sqlite3.
         HOST :   ,                      # Set to empty string for localhost. Not used with sqlite3.
         PORT :   ,                      # Set to empty string for default. Not used with sqlite3.              # Set to empty string for default. Not used with sqlite3.
    }
}

Answer 1

不,ORM不能做任何数据库引擎无法做的事情。

Answer 2

否。如@ignacio-vazquez-abrams所写,一个模型必须在同一数据库中包含所有字段。

BUT

作为替代办法,你可以使用代用模型将两个不同数据库的模型联系起来。

Aim

一种模型应同时提供 Db1 和 db2 的字段

General trick

You have the model ContactMessage from db1, that we will name legacy_db. We suppose you don t want to touch to this model since it comes from another project.
Create a proxy model ProxyContactMessage, it has the same attributes than ContactMessage.
Use a database router to tell Django where to look in legacy_db for ProxyContactMessage objects.
Add a new model ExtendedContactMessage with the fields you would like to add. Declare a OneToOneField with ProxyContactMessage. This data will be saved to your db2 django_db.
Your proxy model cannot hold the new fields since it s abstract, but it can have methods that ask the related ExtendedContactMessage object (if any). Add the callables you want.

Example

在您的 legacy_app/models.py 中, db1 legacy_db 的模型是:

class ContactMessage(models.Model):
    subject = models.CharField(max_length=255)
    message = models.TextField()
    created_at = models.DateTimeField()
    created_by = models.CharField(max_length=255)

    class Meta:
        managed = False
        db_table =  contact_message 

    def __unicode__(self):
        return self.subject

因此您在 myapp/ models. py 中创建 :

class ProxyContactMessage(ContactMessage):
    class Meta:
        proxy = True
        verbose_name =  Contact message 
        verbose_name_plural =  Contact messages 

    def add_extension(self):
        e = ExtendedContactMessage(contact_message=self)
        e.save()
        return e

    def mark_as_processed(self):
        try:
            e = self.extendedcontactmessage
        except ExtendedContactMessage.DoesNotExist:
            e = self.add_extension()
        e.mark_as_processed()

    def processed(self):
        return self.extendedcontactmessage.processed

    def processed_at(self):
        return self.extendedcontactmessage.processed_at

class ExtendedContactMessage(models.Model):
    contact_message = models.OneToOneField(ProxyContactMessage)
    processed = models.BooleanField(default=False, editable=False)
    processed_at = models.DateTimeField(null=True, default=None, editable=False)

    def mark_as_processed(self):
        self.processed = True
        self.processed_at = timezone.now()
        self.save()

请注意, Db2 中只保存非抽象模型 Expended ContactMessage , 因为 ProxycontactMessage 是抽象的。

在 < code> sections. py 中,用类别设置 DATABASE_ROUTERS

class LegacyRouter(object):
    """
    A router to control all database operations on models in the
    legacy database.
    """
    def db_for_read(self, model, **hints):
        if model.__name__ ==  ProxyContactMessage :
            return  legacy_db 
        return None
    def db_for_write(self, model, **hints):
        """
        Attempts to write in legacy DB for ContactMessage.
        """
        if model.__name__ ==  ProxyContactMessage :
            return  legacy_db 
        return None

您的默认路由器将全部发送到 db2 。

最后,你可能有一个管理类,比如:

def mark_as_processed(modeladmin, request, queryset):
    for obj in queryset:
        obj.mark_as_processed()
mark_as_processed.short_description = "Mark as processed"

class ProxyContactMessageAdmin(admin.ModelAdmin):
    list_display = (
         subject ,
         message ,
         created_at ,
         created_by ,
         processed ,
         processed_at ,
    )
    actions = (mark_as_processed,)
admin.site.register(ProxyContactMessage, ProxyContactMessageAdmin)

BUT

Aim

General trick

Example

友情链接