Python Django 多数据库提交具有外键关系的对象

Question

我正在将 Django 与多个数据库一起使用。我有一个“预览”数据库，它接收用户上传的消息，这些消息必须由管理员预览并“接受”，此时它们将被提交到“默认”生产数据库。以下 View 应该可以做到这一点，但我收到错误。每个 newSentenceModel 都有一个指向每个 newMessageSegment 的外键，每个 newMessageSegment 都有一个指向每条消息的外键。如果管理员接受内容，我想将每个项目移动到新数据库，然后删除预览数据库中的旧条目。请帮忙!谢谢-

这是错误:

instance is on database "preview", value is on database "default"

错误消息出现在这一行:

newMessageSegment.msg = newMessage # Setup the foreign key to the msg itself

这是查看功能:

## This view is used when the admin approves content and clicks on the "accept content" button when reviewing 
## a recent upload - it saves the data to the production database
def accept_content(request, msg_id=None):
    if msg_id == None: # If for some reason we got a None, then it's not a valid page to accept so redirect home
        return HttpResponseRedirect("/") # Redirect home
    msgList = Message.objects.using('preview').all() # Get all Messages
    msgSegmentList = MessageSegment.objects.using('preview').all() # Get all MessageSegment Objects
    sentenceModels = SentenceModel.objects.using('preview').all() # Get all SentenceModels
    for msgs in msgList: # Iterate all msgs
        if int(msgs.id) != int(msg_id): # Don't care if it is not the msg needing review
            continue # Short Circuit
        msgPrimaryKey = msgs.pk # Extract the primary key from this msg to restore later
        msgs.pk = None # Erase the primary key so we can migrate databases properly
        newMessage = msgs # This is the msg to transfer to the new one
        newMessage.save(using='default') # Save the item to the production database
        for msgSegment in msgSegmentList: # Iterate all msg segments for this msg
            if msgSegment.msg_id == msgPrimaryKey: # Check the foreign keys on the msg segment to msg connection
                newMessageSegment = msgSegment # Define a new msg segment
                msgSegment.pk = None # Erase the primary key so we can assign it properly
                newMessageSegment.pk = None # Erase the primary key so we can assign it properly
                newMessageSegment.msg = newMessage # Setup the foreign key to the msg itself
                newMessageSegment.save(using='default') # Save the item to the production database
                for sentenceModel in sentenceModels: # Iterate all sentences for this msg segment
                    if sentenceModel.msg_segment_id == msgSegment.id: # Determine which sentences are for this msg segment
                        newSentenceModel = sentenceModel # Define the newSentenceModel
                        newSentenceModel.msg_segment = newMessageSegment # Setup the foreign key to the msg segment
                        newSentenceModel.save(using='default') # Save the item to the production database
                        sentenceModel.delete(using='preview') # Delete the item from the review database
                msgSegment.delete(using='preview') # Delete the item from the review database
        msgs.pk = msgPrimaryKey # Restore the key so we can delete it properly
        msgs.delete(using='preview') # Delete the item from the review database
    return HttpResponseRedirect("/")

Answer 1

Django 会记住保存对象的数据库，因此每个 newMessageSegment 仍然附属于 preview 数据库，直到您将其保存到 default并且它正确地禁止跨数据库 FK 分配。这尚未经过测试，但分配给底层 msg_id 字段可能会起作用:

newMessageSegment.msg_id = newMessage.id

如果失败，您可以创建 newMessageSegment 的新副本，而不仅仅是创建对其的新引用。我认为您可以通过迭代 msgSegment._meta.fields 来实现自动化，但我可能会忽略继承之类的微妙之处。任何多对多字段都会很痛苦。

或者，如果您只是想破解它，请编辑跟踪它的内部对象。我通常不建议这样做，但无论如何，当您保存时它都会改变。

newMessageSegment._state.db = "default"
newMessageSegment.msg = newMessage
newMessageSegment.save(using="default")