django-signals vs triggers?

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I read about django signals (http://docs.djangoproject.com/en/dev/topics/signals/), but as far as I understand, signals are never converted into literal SQL triggers (http://en.wikipedia.org/wiki/Database_trigger).

If I'm correct that signals and triggers are different, then which one is better and in what ways? What's the best practice?

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Here's a concrete example if you want one:

class Location(models.Model):
    name = models.CharField(max_length=30)

class Person(models.Model):
    location = models.ForeignKey('Location')

class Team(models.Model):
    locations = models.ManyToManyField('Location')

I want a person to be able to join a team if and only if that person's location is within that team's set of locations. I do not know how to do that with normal relational constraints, so as far as I know I'm forced to use triggers or signals. My gut says that I should use triggers but I want to know best practice.

triggers django-signals django sql
4 Answers

Main advantages of Triggers over Signals:

  • independent of the application: makes the migration to a new frameworks/languages easier (since triggers and, in some cases, stored procedure are dump with your DB)

  • safety: depending on the situation, you could restrict the UPDATE rights on some tables and still be able to run your app (think of critical history or transaction tables, who knows which exploits might be discovered in the next 10 years)

  • reduce the number of requests your app have to address to the DBMS (especially useful in the context of a distributed architecture).

Here are the main advantages. The main cons is that you have to deal with the old school SQL syntax.

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