如何在django中的模型实例之前保存相关的模型实例？

Question

如何在实例模型之前保存相关模型实例。

这是必要的，因为我想在模型实例save方法下预处理相关模型的实例字段。

我正在Django项目上工作，我处于一种情况，我需要在数据库中保存所有相关模型的实例后运行一些函数。

让说我有一个模型

models.py

from . import signals 
class Video(models.Model): 
    """Video model""" 

    title = models.CharField(
     max_length=255, 
     ) 

    keywords = models.ManyToManyField(
     KeyWord, 
     verbose_name=_("Keywords") 
    ) 

当创建视频模式的新实例。

我需要 1.首先保存所有相关模型。 a。如果相关型号为空，则返回空或无 2.然后保存此视频实例。

我试图使用post_save信号做到这一点，但不能成功，因为不能保证相关模型先保存模型。

from django.db.models.signals import post_save, pre_delete, m2m_changed 
from django.dispatch import receiver 

from .models import Video 


@receiver(m2m_changed, sender=Video) 
@receiver(post_save, sender=Video) 
def index_or_update_video(sender, instance, **kwargs): 
    """Update or create an instance to search server.""" 
    # TODO: use logging system 
    # Grab the id 
    print("Id is", instance.id) 
    # Keywords is empty as keyword instance is saved later than this instace. 
    keywords = [keyword.keyword for keyword in instance.keywords.all()] 
    print(keywords) # [] empty no keywords 
    instance.index() 


@receiver(pre_delete, sender=Video) 
def delete_video(sender, instance, **kwargs): 
    print("Delete index object") 
    instance.delete() 

更新：

可以抓取post_save信号来实现，并等待unitls 其相关模型得到保存在数据库中，当related_models得到保存 开始序列化进程，并创建一个沿平JSON文件模型字段及其相关实例如此，平坦的json文件可以将 索引到弹性搜索服务器中。

问题白羊座，我们应该在信号处理器方法中等待多少时间？以及如何知道在db中保存的所有实例相关字段。

class Video(models.Model): 
    def save(self, *args, **kwargs): 
     # 1. Make sure all of its related items are saved in db 
     # 2. Now save this instance in db. 
     # 3. If the model has been saved. Serialize its value, 
     # 4. Serailize its related models fields 
     # 5. Save all the serialized data into index server 

     # The advantage of using this is the data are indexed in real 
     # time to index server. 

     # I tired to to implement this logic using signals, in case of 
     # signals, when the instance get saved, its related models are 
     # not instantly available in the databse. 

     # Other solution could be, grab the `post_save` signals, wait(delay 
     # the serialization process) and start the serialization of 
     # instance model and it's related to convert the data to flat json 
     # file so, that it could index in the searching server(ES) in real 
     # time. 


     # until the instance related models get saved and start to 
     # serialize the data when its 

Answer 1

您可以在保存实例前覆盖模型的save()方法并保存相关模型（对象）。

Answer 2

通过我使用Django的管理员，我不限定 的逻辑视图方式，增加了相关模型实例由Django管理

处理。在这种情况下，您可以翻转ModelAdmin调用save_model()和save_related()以便从Model.save()开始的顺序，您将能够达到相关字段的更新值，如this post中所述。

class Video(models.Model): 

    def save(self, *args, **kwargs): 
     if not self.id: 
      super().save(*args, **kwargs) 
     all_updated_keywards = self.keywards.all() 
     ... 
     super().save(*args, **kwargs) 


class VideoAdmin(admin.ModelAdmin): 

    def save_model(self, request, obj, form, change): 
     if not obj.pk: 
      super().save_model(request, obj, form, change) 
     else: 
      pass 

    def save_related(self, request, form, formsets, change): 
     form.save_m2m() 
     for formset in formsets: 
      self.save_formset(request, form, formset, change=change) 
     super().save_model(request, form.instance, form, change)