Model

Django Basic Flow

1. Define url

   • urls.py is a signpost!

2. Create function to execute in views.py

3. Create html to return

Django project / app configuration

• Django has a structure where one project has multiple apps

• Each app has an MTV pattern

• When composed of multiple apps, name duplication is possible, so structure as template/{app name}/{}.html

  • why?

    • Subdirectories of templates folder created in individual apps are used as template files (default)

    • Django follows the declaration order of DIR and INSTALLED_APPS in settings.py when searching for template files, so to prevent name duplication, create a folder with the same name as the app name under template

1. Project creation

django-admin startproject {project name}

2. Project basic configuration - settings.py

# Build paths inside the project like this: os.path.join(BASE_DIR, ...)
BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))

TEMPLATES = [
    {
        'BACKEND': 'django.template.backends.django.DjangoTemplates',
        # What to specify when you want to create templates in a folder other than app/templates/
        'DIRS': [os.path.join(BASE_DIR, 'templates')], # If you create a `templates` folder in the project root path, just `templates`
        # See all templates folders in registered apps as the same templates => True
        'APP_DIRS': True,
        'OPTIONS': {
            'context_processors': [
                'django.template.context_processors.debug',
                'django.template.context_processors.request',
                'django.contrib.auth.context_processors.auth',
                'django.contrib.messages.context_processors.messages',
            ],
        },
    },
]

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': os.path.join(BASE_DIR, 'db.sqlite3'),
    }
}

3. Create app (articles)

• App names are generally composed in plural form

  python manage.py startapp articles

• App registration

  settings.py

  INSTALLED_APPS = [
      'django.contrib.admin',
      'django.contrib.auth',
      'django.contrib.contenttypes',
      'django.contrib.sessions',
      'django.contrib.messages',
      'django.contrib.staticfiles',
      'articles',
      'django_extensions',
  ]

4. Create urls.py

Project folder

from django.contrib import admin
from django.urls import path, include

urlpatterns = [
    path('admin/', admin.site.urls),
    path('articles/',include('articles.urls'))
]

Individual app

from django.urls import path
from . import views

urlpatterns = [
    #/articles/
    path('new/', views.new),
    path('create/', views.create),
    path('', views.index),
    ]

Role of MTV

view

• url

• request (request related information)

• return render()

Template

• html

• DTL

• loop / conditional / filter

Model

• DB

Model in Django

Model

: Single source of information about Data

Migrations

: A method to reflect model changes to the database schema

Migration Flow

1. Model creation/modification/deletion etc.

2. Create migration file

   • Migration file records model changes and consists of code to reflect them in the database

   • Think of migration file as a version control system for database schema! -> git

3. Apply to database through migrate

Model	Migration	ORM (Query methods, QuerySet API)
Data management in MTV pattern	Reflect db schema defined by Model	Query statements that manipulate db (possible through Python object manipulation)

Model usage

1. Model definition

models.py

from django.db import models

# Create your models here.

class Article(models.Model):
    title = models.CharField(max_length=140)
    content = models.TextField()
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)

• Create a class that inherits from models.Model

• For attributes, specify the column names of the table you want to compose, and define fields according to data types

• ID field is automatically created as pk value.

• Field and option information defined above is as follows:

  • CharField:

    • max_length: Required

  • DateTimeField

    • auto_now_add: (Optional) Automatically set the time value only when creating

    • auto_now: (Optional) Automatically set the time value every time it's modified

  • For other fields, check the link https://docs.djangoproject.com/ko/2.1/ref/models/fields/#field-types!

CharField vs TextField()

: Choose based on whether to receive data with <input> or <textarea> when actually receiving data with <form> tag

2. migration

Migrations are Django's way of propagating changes you make to your models (adding a field, deleting a model, etc.) into your database schema. Migration is a method for reflecting model changes to the database schema in django.

2-1. makemigrations

$ python manage.py makemigrations
Migrations for 'articles':
  articles/migrations/0001_initial.py
    - Create model Article

• To reflect the defined model in the database, create a migration file through the migration command

• Migration files record model changes and are recorded in the migrations/ folder for each app. Initially, a file called 0001_initial.py will be created.

• Migration file manages model changes

  • Preparing to reflect modeled content in db!

2-2. migrate

$ python manage.py migrate
Operations to perform:
  Apply all migrations: admin, articles, auth, contenttypes, sessions
Running migrations:
  Applying contenttypes.0001_initial... OK
  Applying auth.0001_initial... OK
  Applying admin.0001_initial... OK
  Applying admin.0002_logentry_remove_auto_add... OK
  Applying admin.0003_logentry_add_action_flag_choices... OK
  Applying articles.0001_initial... OK
  Applying contenttypes.0002_remove_content_type_name... OK
  Applying auth.0002_alter_permission_name_max_length... OK
  Applying auth.0003_alter_user_email_max_length... OK
  Applying auth.0004_alter_user_username_opts... OK
  Applying auth.0005_alter_user_last_login_null... OK
  Applying auth.0006_require_contenttypes_0002... OK
  Applying auth.0007_alter_validators_add_error_messages... OK
  Applying auth.0008_alter_user_username_max_length... OK
  Applying auth.0009_alter_user_last_name_max_length... OK
  Applying sessions.0001_initial... OK

• Command to reflect created migration file to database

• The reason it looks like a lot is because database migration files that django uses by default are also reflected

  • From now on, do python manage.py migrate as soon as you create a project!

Migration Flow

• Create migration

  python manage.py makemigrations

• Check migration DB reflection status

  python manage.py showmigrations

• Output SQL statement corresponding to migration

  python manage.py sqlmigrate app_label migration_name

• Finally reflect migration file content to DB

  python manage.py migrate

+

admin registration

# django_crud/articles/admin.py
from django.contrib import admin

# Register your models here.
from .models import Article
admin.site.register(Article)

Django ORM

Basic database manipulation is called CRUD(Create, Read, Update, Delete) operation.

ORM (Object Relational Mapping)

• Programming technique to convert incompatible data between DB and OOP language

  • ORM maps values stored in db to objects!

    • Manipulating db through Python object manipulation (method calls)!

Django shell

A function that allows you to use python interactive interpreter for django projects

python manage.py shell

• Can be used conveniently through additional package installation.

  pip install django-extensions ipython

  • django-extensions basically provides useful functions for django development.

    • https://github.com/django-extensions/django-extensions

  • ipython is installed to use interactive shell more conveniently

• After installation, add the following content to settings.py. (mind the comma)

  # django_crud/settings.py
  INSTALLED_APPS = [
      ...
      'django_extensions',
      'articles',
  ]

• And from now on, use the following command.

  python manage.py shell_plus

1. Create

article = Article()
article.title = '제목'
article.content = '내용'
article.save()

2. Read

• Read all data

  Article.objects.all()
  >> <QuerySet [<Article: Article object (1)>]>

• Read single data

  Single data inquiry is possible through unique value id.

  Article.objects.get(id=1)
  >> <Article: Article object (1)>

  In [2]: Article.objects.get(id=3)                                         
  Out[2]: Title: sample title & Content: sample content
  
  In [3]: Article.objects.get(pk=3)                                         
  Out[3]: Title: sample title & Content: sample content

  • id == pk!

    • Does not allow duplicates

3. Update

a1 = Article.objects.get(id=1)
a1.title = '제목 수정'
a1.save()

• To check if it was modified, query the data again

4. Delete

a1 = Article.objects.get(id=1)
a1.delete()
>> (1, {'articles.Article': 1})

Using Admin Page

1. Create administrator account

$ python manage.py createsuperuser
사용자 이름 (leave blank to use 'ubuntu'): admin1
이메일 주소:
Password:
Password (again):
Superuser created successfully.

2. admin registration

To use the admin page, it must be defined in admin.py for each app

# django_crud/articles/admin.py
from django.contrib import admin

# Register your models here.
from .models import Article
admin.site.register(Article)

3. Verification

• Access /admin/ url and log in with administrator account

+

Tips

$ python manage.py sqlmigrate articles 0001
BEGIN;
--
-- Create model Article
--
CREATE TABLE "articles_article" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "title" varchar(20) NOT NULL, "content" text NOT NULL);
COMMIT;

Fat Model

• MVC

  • M (C) V

• MTV

  • M (V) T

-> Make model fat!!!!