Django - 在admin中保存更新另一个模型

Question

I am using django to create a video library website.

I have 3 models for the library: Video, VideoTopic, and Course.

I have a TimedeltaField for the duration of each Video. Upon saving each video in admin, I want to get the sum of each TimedeltaField for all Videos within a Course, then save that sum to a TimedeltaField in my Course model.

I'm using django-timedeltafield , which will handle the summarization very well. What I have yet to find a solution for is how to update the Course model after I save each Video in admin. Any advice?

My models are as follows:

class Video(models.Model):
    title = models.CharField(max_length=200)
    topic = models.ForeignKey('VideoTopic')
    duration = timedelta.fields.TimedeltaField(default="3 minutes, 30 seconds", help_text="(x minutes, x seconds)")

class VideoTopic(models.Model):
    name = models.CharField(max_length=200, blank=True)
    course = models.ForeignKey('course.Course')

class Course(models.Model):
    name = models.CharField(max_length=200)
    duration = timedelta.fields.TimedeltaField()

Answer 1

I recommend you use a django signal . This will ensure your models are synchronized regardless of where they are updated (in the app, admin, etc.).

Register the post save signal on the Video. In the signal, you will receive the video instance. Simply query for its related records in VideoTopic and Course and do the math there. I recommend doing all this in the transaction if you don't want it to ever fail. If you don't need the information always up-to-date, it's also an opportunity to do some background work to make the save lighter weight.

Why a signal?

• Separates concerns
• Ensures your logic always runs
• Can help decouple things out of the model directly if it has dependencies, which can cut down on some situations of loading order/circular dependencies.

Alternatively, you could simply override the Video model's save method and do the same thing there. In either case, just use the related properties in the ORM from your foreign keys if you don't want to write the queries yourself.

Answer 2

An alternative is to override the admin save method to update the course model. See https://docs.djangoproject.com/en/dev/ref/contrib/admin/#modeladmin-methods .