Python Django 多个数据库提交具有外键关系的对象

Question

我将 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”，此时它们被提交到“默认”生产数据库。以下视图应该做到这一点，但我得到一个错误。每个 newSentenceModel 对每个 newMessageSegment 都有一个外键，每个 newMessageSegment 对每个消息都有一个外键。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"

错误信息出现在这一行：

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

这里是视图函数：

## 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 仍然隶属于 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。这是未经测试的，但它可能会分配给底层的msg_id 字段：

newMessageSegment.msg_id = newMessage.id

如果不这样做，您可以创建newMessageSegment 的新副本，而不仅仅是创建对它的新引用。我认为你可以通过迭代msgSegment._meta.fields 来自动化它，但我可能会忽略继承或其他东西的微妙之处。而且任何多对多的字段都会很痛苦。

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，但无论如何保存时都会更改它。

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