Reputation: 25554

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

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 the inserts to this model.

Alternative 1

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

    def __unicode__(self):
        return str(self.field1.id)

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

    def insert_history(self):
        # Here I will have some business logic to insert the data to the history model

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

My questions here are:

The code above is correct?

If yes, how can I call the "insert_history" from a view?

Alternative 2

I've another alternative that I've tested and it works, but does not feel the right way. The code looks like this:

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

    def __unicode__(self):
        return str(self.field1.id)

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

def insert_history(field1, field2, field3):
    # Here I will have some business logic to insert the data to the history model

And I call it from a view like this:

from app.models import insert_history

insert_history('1', True, 'some_date')

what is the correct way of doing it? If the alternative 1 is correct, how can I call the "insert_history" from a view?

Best Regards,

Upvotes: 18

Answers (5)

NKortesmaa

Reputation: 11

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

Upvotes: 1

skoll

Reputation: 2452

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

Upvotes: 15

Burhan Khalid

Reputation: 174614

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.

Upvotes: 4