Django Models

Django Models WELCOME TO LEVEL 2!

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Django Models level 2 • SQL • Migrations • Relations (Basic)

SQL Database title content location My First Trip ᡙࢠ޷ծɼ٣ॄኄ޷䏆? ୆๺Րं᜾ Django େ๯ᯃ ኺᯩଶ౸ಈଶ ୆๺ࢢେ҆ე෮ڵೆ࿏ Ұஈ293ᥒ … … …

Post.objects.all() SELECT * FROM trips_post Python SQL * Rough translation

Post.objects.filter( location='ডӡେ҆᜾' ) SELECT * FROM trips_post WHERE location="ডӡେ҆᜾" Python SQL * Rough translation

ORM query SQL query Query results Model object Django Django SQL database

class Post(Model): title = CharField(max_length=100) content = TextField(blank=True) location = CharField(max_length=100)

class Post(Model): title = CharField(max_length=100) abstract = CharField( max_length=100, blank=True) content = TextField(blank=True) location = CharField(max_length=100)

>>> posts = Post.objects.all() >>> print(posts[0].abstract) Traceback (most recent call last): … django.db.utils.OperationalError: no such column: trips_post.abstract >>>

Migrations • When model change requires database change • Synchronisation • Schema or data migration

$ python manage.py makemigrations trips Migrations for 'trips': 0002_post_abstract.py: - Add field abstract to post

trips ├── __init__.py ├── admin.py ├── migrations │ ├── 0001_initial.py │ ├── 0002_post_abstract.py │ └── __init__.py ├── models.py ├── tests.py └── views.py

$ python manage.py migrate trips Operations to perform: Apply all migrations: trips Running migrations: Rendering model states... DONE Applying trips.0002_post_abstract... OK

>>> posts = Post.objects.all() >>> print(posts[0].abstract) >>>

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Relational Database title author content location … Post name email Author

class Author(models.Model): name = models.CharField(max_length=50) email = models.EmailField() def __str__(self): return self.name

$ python manage.py makemigrations trips Migrations for 'trips': 0003_author.py: - Create model Author $ python manage.py migrate trips Operations to perform: Apply all migrations: trips Running migrations: Rendering model states... DONE Applying trips.0003_author... OK

>>> from trips.models import Author >>> Author.objects.create( ... name='Django Girls Taipei', ... email='taipei@djangogirls.org') >>>

class Author(models.Model): … class Post(models.Model): title = models.CharField(max_length=100) author = models.ForeignKey(Author) …

$ python manage.py makemigrations trips You are trying to add a non-nullable fi Please select a fix: 1) Provide a one-off default now (will 2) Quit, and let me add a default in m Select an option: _

$ python manage.py makemigrations trips You are trying to add a non-nullable fi Please select a fix: 1) Provide a one-off default now (will 2) Quit, and let me add a default in m Select an option: 1 Please enter the default value now, as The datetime and django.utils.timezone >>> 1

$ python manage.py makemigrations trips You are trying to add a non-nullable fi Please select a fix: 1) Provide a one-off default now (will 2) Quit, and let me add a default in m Select an option: 1 Please enter the default value now, as The datetime and django.utils.timezone >>> 1 Migrations for 'trips': 0004_post_author.py: - Add field author to post

$ python manage.py migrate trips Operations to perform: Apply all migrations: trips Running migrations: Rendering model states... DONE Applying trips.0004_post_author... OK

>>> from trips.models import Post >>> posts = Post.objects.all() >>> posts[0].author >>> posts[0].author.name 'Django Girls Taipei'

Exercises • Add abstract field in Post • Add Author model • Add author foreign key in Post • Display author in template

Hint templates/post.html