Django - Function inside a model. How to call it from a view?

Question

I\'m designing a model in Django but I don\'t know if this is the best way. I have a model called \"History\" and inside this model I\'ve a specialized function that will handle

Answer 1

Just select your History instance (eg. with primary key 1):

hist = History.objects.get(pk=1)

...and call your method using the hist variable:

hist.insert_history(...)

Answer 2

I think that it is most appropriate to use custom manager https://docs.djangoproject.com/en/dev/topics/db/managers/ for this problems.

Answer 3

Does insert_history use self? Or does it create a new History object?

If it creates a new object, I'd do it like this:

class History(models.Model):
    @classmethod
    def insert_history(cls, field1, field2, field3):
        # Here be code

To call it

from app.models import History
History.insert_history(field1, field2, field3)

BTW, the conventional name for a method creating new objects is create. Also, have a look at https://docs.djangoproject.com/en/1.9/ref/models/instances/#creating-objects

Answer 4

Just to extend on answer by @burhankhalid, as I were unable to comment due to rather high-ish rep requirement, I had a similar need to alter another model while saving mine, but solution proposed by Burhan Khalid helped me to start.

The model I needed to modify, I had a reference-to from this one

My proposal assumes that Request would have a 'attrib1', and to that it tries to save the value from History.field2

class History(models.Model):
field1 = models.ForeignKey(Request)
field2 = models.BooleanField()
field3 = models.DateTimeField()

def __unicode__(self):
    return unicode(self.field1.id) # __unicode__ should return unicode,
                                   # not string.

class Meta: #
    ordering = ['-field3']

def save(self, *args, **kwargs):
    self.field3 = your calculated value
    self.field1.attrib1 = self.field2  # for instance
    self.field1.save()  # don't forget to save the other 
    super(History, self).save(*args, **kwargs)

So the whole concept of rewriting the save() method and modifying (and saving) other objects as well made the difference

Answer 5

To insert data to the History model I will always have to use the insert_history function.

Yes, it will set the field3, a datetime, based on some logic that I will write inside insert_history

The easiest way is to override the save method:

class History(models.Model):
    field1 = models.ForeignKey(Request)
    field2 = models.BooleanField()
    field3 = models.DateTimeField()

    def __unicode__(self):
        return unicode(self.field1.id) # __unicode__ should return unicode,
                                       # not string.

    class Meta: #
        ordering = ['-field3']

    def save(self, *args, **kwargs):
        self.field3 = your calculated value
        super(History, self).save(*args, **kwargs)

Now, whenever you save your method - field3's value will be whatever is the result of the calculation in your custom save method. You don't need to modify anything in your views for this to work.