Retail Website built with Django P1 (2020-02-04)

Django:

templates builtins!!!

very useful template shortcuts, tags and many more...

Class based views: Generic VIEWS

learning source:
codingforentrepreneurs
generic views official documentation

to iterate through a folder

StackO: iterate through a static image folder in django:

This isn't something Django has built in. But Django is just Python, and you can use normal Python file functions to get your list in the view:

files = os.listdir(os.path.join(settings.STATIC_ROOT, "styles/jamia"))

filter in queryset

When you know what to look for:
category_handbags = Category.objects.filter(name='Handbags')
furthur reading: Database Functions

* filter()

By using filter(), we can retrieve a QuerySet of just those books that were published within the last 90 days period, like so:

from datetime import datetime, timedelta 
Book.objects.filter(date_published__gte=datetime.now() - timedelta(days=90)).count()
# __isnull
Book.objects.filter(author__isnull=True).count()
# __exact
Book.objects.filter(title__exact='').count()

* exclude()

if we use the exact same date_published example above but swap out filter() for exclude(), we’d expect the resulting book count to be the inverse: from 3 of 20 to now 17 of 20:

from datetime import datetime, timedelta
Book.objects.exclude(date_published__gte=datetime.now() - timedelta(days=90)).count()
# combining filters
Book.objects.exclude(author__isnull=True).exclude(title__exact='').count()

categories.count() vs len(categories)

len() loads all the data in memory then do the counting

count() is normally faster when the data is not pre loaded
be careful not to count a queryset manager like categories.first().count() will prompt AttributeError; however, categories.first().subcategory_set.count() will tell you the number of its subcategories correctly and it's the same as len(categories.first().subcategory_set.all()), as you can see, ALL of the subcategories are read to count the length.

Django - Images:

ImageField

To add ImageField in a model and to load the image in the database onto your web:
ref: William Vincent
ref: GeeksforGeeks

uploaded images in wrong orientation:

photos taken by phones have this problem sometimes, the post by Giovanni solved the problem:

from django.db.models.signals import post_save
from django.dispatch import receiver
from PIL import Image, ExifTags
from django.db import models
import os

class Item(models.Model):
    name = ...

class ItemImage(models.Model):
    item = models.ForeignKey(Item)
    image = models.ImageField(upload_to='itemimages', null=True, blank=True)

# solves the problem that uploaded images are in wrong orientation
def rotate_image(filepath):
    try:
        image = Image.open(filepath)
        for orientation in ExifTags.TAGS.keys():
            if ExifTags.TAGS[orientation] == 'Orientation':
                break
        exif = dict(image._getexif().items())

        if exif[orientation] == 3:
            image = image.rotate(180, expand=True)
        elif exif[orientation] == 6:
            image = image.rotate(270, expand=True)
        elif exif[orientation] == 8:
            image = image.rotate(90, expand=True)
        image.save(filepath)
        image.close()
    except (AttributeError, KeyError, IndexError):
        # cases: image don't have getexif
        pass


@receiver(post_save, sender=ItemImage, dispatch_uid="update_image_item")
def update_image(sender, instance, **kwargs):
  if instance.image:
    BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
    fullpath = BASE_DIR + instanc.image.url
    rotate_image(fullpath)

furture reading: FIX UPLOADED IMAGES IN PYTHON WEBAPPS

image files in image field deleted but the file remains in the MEDIA foler

Cleanup Files (and Images) On Model Delete in Django

ref: Online Retail websites

• asos: most referenced in item displaying style, categorisation filtering, most responsive
• LOUIS VUITTON: most elegant in wording and minimalistic in styling
• BOTTEGA VENETA: not responsive enough on laptop
• ACCESSORIZE LONDON: not responsive enough on laptop
• KUPIVIP: looks cheap

django-bootstrap4

containers, row and columns

containers and grid examples

col-sm-12: when page is 'small' width, occupy 12 columns

col-md-6: when page is 'medium' width, occupy 6 columns

col-lg-4: when page is 'large' width, occupy 4 columns

col-4: At ALL time, occupy 4 columns, unless other rules applied

col-md-auto: when page is 'medium' width, occupy whatever columns remain

Default grid settings: docs/4.4/layout/grid

$grid-columns:      12;
$grid-gutter-width: 30px;

$grid-breakpoints: (
  xs: 0,      // Extra small screen / phone
  sm: 576px,  // Small screen / phone
  md: 768px,  // Medium screen / tablet
  lg: 992px,  // Large screen / desktop
  xl: 1200px  // Extra large screen / wide desktop
);

$container-max-widths: (
  sm: 540px,
  md: 720px,
  lg: 960px,
  xl: 1140px
);

Simply Python:

to iterate through a dictionary:

dict.keys() method and dict.items() method

# using dict.keys() method
D1 = {1:'a', 2:'b', 3:'c'} 
for key in D1.keys():
    print(k, D1[k])
# 1 a
# 2 b
# 3 c

# using dict.items() method
for key, value in D1.items()
    print(key, value)
# same result