Chapter 6: I don't get an AttributeError: 'List' object has no attribute 'save'

[Paul Spiteri]

Hi

Sorry for another question (hope you received my thanks for the previous one), but I had a couple of cracks at this - using git I wound back to a version that worked in line with (your great) book and started from there twice and I got the same difference twice, which eventually led me to a hole I couldn't get out of, so I thought I'd pipe up.

Anyhoo, just after the Adjusting Our Models section of Chapter 6 you leave use (i.e. your readers) to our own devices to add some code to correct the unit test errors that present themselves.

The first error is ...

ImportError: cannot import name 'List'

... to which I added some code - 

# models.py

class List(models.Model):

    pass

I then got another error not listed in the book - 

django.db.utils.OperationalError: no such table: lists_list

So I figure I need to make a migration with - 

python manage.py makemigrations

Oh, python above is 3.4.1 - trust me, I just checked. Then I get the following error - 

AttributeError: 'Item' object has no attribute 'list'

See what happened here? I didn't get the "I don't get an AttributeError: 'List' object has no attribute 'save'" error. Now the first time I wen't through the exercise I just ignored this - I mean one less error ... that's great. But then I get further into the exercise and it all goes to pot. For example, in the 'XYZ' section of this chapter I get an error message ...

sqlite3.IntegrityError: NOT NULL constraint failed: lists_item.list_id

... rather than the expected ...

File "/workspace/superlists/lists/views.py", line 14, in new_list
Item.objects.create(text=request.POST['item_text'])

... and if I ignore the difference in that error message I end up with an error ...

lists.models.DoesNotExist: Item matching query does not exist.

And by this stage the whole thing has gone belly up. I think it has something to do with the fact that I don't receive the "'List' object has no attribute 'save'" error message.

I'll past my test in below, just in case it is useful - please bear in mind that the test below only goes up to the point where I get the "AttributeError: 'Item' object has no attribute 'list'" error .. because after that time I am pretty sure I have compromised it beyond all recognition.

Thanks again and hope you're having a great day (or had a great weekend, assuming you won't get to this till Monday, in whatever timezone your in) - Paul

from django.test import TestCase

from django.core.urlresolvers import resolve

from django.http import HttpRequest

from lists.views import home_page

from django.template.loader import render_to_string

from lists.models import Item, List

class HomePageTest(TestCase):

    def test_root_url_resolves_to_home_page_view(self):

        found = resolve('/')

        self.assertEqual(found.func, home_page)

    def test_home_page_returns_correct_html(self):

        request = HttpRequest()

        response = home_page(request)

        expected_html = render_to_string('home.html')

        self.assertEqual(response.content.decode(), expected_html)

class ListAndItemModelTest(TestCase):

    def test_saving_and_retrieving_items(self):

        list_ = List()

        list_.save()

        first_item = Item()

        first_item.text = 'The first (ever) list item'

        first_item.list = list_

        first_item.save()

        second_item = Item()

        second_item.text = 'Item the second'

        second_item.list = list_

        second_item.save()

        saved_list = List.objects.first()

        self.assertEqual(saved_list, list_)

        saved_items = Item.objects.all()

        self.assertEqual(saved_items.count(), 2)

        first_saved_item = saved_items[0]

        second_saved_item = saved_items[1]

        self.assertEqual(first_saved_item.text, 'The first (ever) list item')

        self.assertEqual(first_saved_item.list, list_)

        self.assertEqual(second_saved_item.text, 'Item the second')

        self.assertEqual(second_saved_item.list, list_)

class ListViewTest(TestCase):

    def test_uses_list_template(self):

        response = self.client.get('/lists/the-only-list-in-the-world')

        self.assertTemplateUsed(response, 'list.html')

    def test_displays_all_items(self):

        Item.objects.create(text='itemey 1')

        Item.objects.create(text='itemey 2')

        # request = HttpRequest()

        # response = home_page(request)

        response = self.client.get('/lists/the-only-list-in-the-world')

        self.assertContains(response, 'itemey 1')

        self.assertContains(response, 'itemey 2')

class NewListTest(TestCase):

    def test_saving_a_POST_request(self):

        self.client.post(

            '/lists/new',

            data={'item_text': 'A new list item'}

        )

        self.assertEqual(Item.objects.count(), 1)

        new_item = Item.objects.first()

        self.assertEqual(new_item.text, 'A new list item')

    def test_redirects_after_POST(self):

        response = self.client.post(

            '/lists/new',

            data={'item_text': 'A new list item'}

        )

        self.assertRedirects(response, '/lists/the-only-list-in-the-world/')

[Agustín Scaramuzza]

Can we see your whole models.py code?

[Paul Spiteri]

Sure - but it doesn't look much different from the example in the book because I am asking why I am not getting the "'List' object has no attribute 'save'" error message because I think it is that which is causing the problems I am getting later on in the exercise.

Thanks for taking the time to read my question - Paul 

from django.db import models

class List(models.Model):

    pass

class Item(models.Model):

    text = models.TextField(default='')

    list = models.ForeignKey(List, default=None)

[Agustín Scaramuzza]

Have you tried deleting all the migration files but the first one and running makemigrations again?

[Paul Spiteri]

Well what do you know - it worked. I don't understand why, but I am on my way now so no complaints from me.

Thanks heaps, AS, for helping out.

[Harry Percival]

Hi Paul,

Just picking up on this, a couple of decades after you posted it I know, but still...

Here's what you said:

The first error is ...

ImportError: cannot import name 'List'

... to which I added some code - 

# models.py

class List(models.Model):

    pass

I then got another error not listed in the book - 

django.db.utils.OperationalError: no such table: lists_list

In fact the "no such table" error is absolutely listed in the book, but it's meant to be the next-but-one expected failure.  The reason you're not seeing "List has not attribute save" is because you've gone too fast. Your first step should have been

    class List(object):

        pass

But you inherited from models.Model straight away.  Not wrong necessarily, but smaller steps are the name of the game in this exercise...

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[Paul Spiteri]

Hi Harry (the Australian in me wants to abbreviate that to H, but I appreciate this may not be everyone's cup of tea. Pun not intended.)

Thanks for picking this up. The only reason I flagged this in the first instance was that later ... a fair way ... down the track I got an error that I assumed was because of this one. In hindsight, this was probably hindsight.

My progress through the exercises have lagged a bit. I think my absorption of some testing principles and algorithms was getting lost on having to pick up some Django basics, which I think I've gone a long way to addressing now having whipped up a reasonably complex app over the weekend. I'll rebuild it TDD style, promise! One more week and I'll be back onto the exercises. 

More then.

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