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。
我正在处理 Django 项目,并且在所有相关的实例模型都保存在数据库中之后,我需要运行一些函数。
假设我有一个模型
模型.py
from . import signals
class Video(models.Model):
"""Video model"""
title = models.CharField(
max_length=255,
)
keywords = models.ManyToManyField(
KeyWord,
verbose_name=_("Keywords")
)
创建视频模型的新实例时。
我需要 1. 首先保存所有相关模型。一个。如果相关模型为空,则返回空或无 2. 然后保存此视频实例。
我尝试使用post_save
信号来做到这一点,但无法成功,因为无法保证相关模型会先于模型保存。
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:
可以通过抓取post_save
信号并等待unitls其相关模型保存在db中来实现,当related_models保存时开始序列化过程并创建平面json文件以及模型字段及其相关实例,因此平面json文件可以索引到弹性搜索服务器。
还有一个问题,我们应该在信号处理方法中等待多少时间?以及如何知道所有与实例相关的字段都保存在数据库中。
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