Allow only one instance of a model in Django

Question

I would like to control some configuration settings for my project using a database model. For example:

class JuicerBaseSettings(models.Model):
    max_rpm =         


        

Answer 1

You can override save method to control number of instances:

class JuicerBaseSettings(models.Model):

    def save(self, *args, **kwargs):
        if not self.pk and JuicerBaseSettings.objects.exists():
        # if you'll not check for self.pk 
        # then error will also raised in update of exists model
            raise ValidationError('There is can be only one JuicerBaseSettings instance')
        return super(JuicerBaseSettings, self).save(*args, **kwargs)