Django Girls Advanced - Models: Level 2

http://www.meetup.com/Taipei-py/events/225986103/

Transcript

1. Django Models
   

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2. Django Models
   WELCOME TO LEVEL 2!
   

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

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

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

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

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

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

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

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

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

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

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

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

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

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18. Relational Database
    title
    author
    content
    location
    …
    Post
    name
    email
    Author
    

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

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20. $ 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
    

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

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

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23. $ 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: _
    

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24. $ 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
    

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25. $ 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
    

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

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

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

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29. Hint
    
    By
    
    {{ post.author.name }}
    
    
    templates/post.html
    

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