====== Django Models ======
===== Migrations =====

<code>
$ python manage.py makemigrations <app>
</code> 
Will create migration files for all the apps if the ''app'' was not indicated.

<code>
$ python manage.py migrate
</code> 
Will apply migrations to the configured DB.
===== Signals =====

==== Ways to connect signals ====
<code python>
class Award(models.Model):
    name = models.CharField(max_length=200, unique=True)
    ...

    @classmethod
    def pre_save(cls, sender, instance, **kwargs):
        ...

pre_save.connect(Award.pre_save, sender=Award)
</code>
<code python>
from django.contrib.auth.models import User
from django.db.models.signals import post_save
from django.dispatch import receiver

class Profile(models.Model):
    user = models.OneToOneField(User, on_delete=models.CASCADE)
    bio = models.TextField(max_length=500, blank=True)
    location = models.CharField(max_length=30, blank=True)
    birth_date = models.DateField(null=True, blank=True)

@receiver(post_save, sender=User)
def create_user_profile(sender, instance, created, **kwargs):
    if created:
        Profile.objects.create(user=instance)

@receiver(post_save, sender=User)
def save_user_profile(sender, instance, **kwargs):
    instance.profile.save()
</code>
===== Model configuration =====

==== Modelos proxy ====
Proxy models are used to modify Python behaviour of a model by extending a model class. Database tables aren't generated for proxy models. So you can't use a proxy model for AUTH_USER_MODEL.
<code>
class Badge(models.Model):
    name = ...
    color = ... # gold/silver


class GoldBadge(Badge)
    class Meta:
        proxy = True

    def award(self, user):
        # award a gold badge to user

class SilverBadge(Badge):
    class Meta:
        proxy = True

    def award(self, user):
        # award a silver badge to user
</code>

===== Fields =====
==== DateTime Field ====
The auto_now_add will set the timezone.now() only when the instance is created, and auto_now will update the field everytime the save method is called.

<code python>
class Invoice(models.Model):
    description = models.CharField(max_length=255)
    status = models.CharField(max_length=10)
    vendor = models.ForeignKey(Vendor)
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)
</code>
==== Image Field ====

Model:
<code>
cover = models.ImageField(null=True)
</code>

Template:
<code>
{% if object.cover %}
<img src="{{ object.cover.url }}"></img>
{% endif %}
</code>

Config:
<code python>
MEDIA_URL = '/media/'
MEDIA_ROOT = os.path.join(BASE_DIR, '../media')
</code>

Urls:
<code python>
from django.contrib.staticfiles.urls import static
from django.conf import settings

urlpatterns += static(settings.MEDIA_URL, document_root=settings.MEDIA_ROOT)
</code>


==== Choice ====
<code>
from django.db import models

class Person(models.Model):
    SHIRT_SIZES = (
        ('S', 'Small'),
        ('M', 'Medium'),
        ('L', 'Large'),
    )
    name = models.CharField(max_length=60)
    shirt_size = models.CharField(max_length=2, choices=SHIRT_SIZES)
</code>
Get its values
<code>
>>> p = Person(name="Fred Flintstone", shirt_size="L")
>>> p.save()
>>> p.shirt_size
'L'
>>> p.get_shirt_size_display()
'Large'
</code>
==== Special fields ====

<code>
id = models.UUIDField(primary_key=True, default=uuid4, help_text="Unique ID for this particular video")
</code>

==== Fields configuration ====

=== Choice ===
<code python>
import calendar

...

class MyModel(models.Model):
    ...

    MONTH_CHOICES = [(str(i), calendar.month_name[i]) for i in range(1,13)]

    month = CharField(max_length=9, choices=MONTHS_CHOICES, default='1')
</code>



===== How to... =====
==== Deal with performed queries ====
See the current registered queries (with their times):
<code>
from django.db import connection
connection.queries
</code>

See a concrete database queries:
<code>
from django.db import connections
connections['my_db_alias'].queries
</code>

Delete the query array:
<code>
from django.db import reset_queries
reset_queries()
</code>
==== Get an app model ====
<code>
from django.apps import apps
apps.get_model('users', 'BaseUser')
</code>

==== Choose a random element from DB ====
<code>
reg = Work(title=random_string_generator(random.randint(5, 15), True),
           license=License.objects.order_by('?').first(),
           description=random_string_generator(random.randint(200,2000), True),
           created=str_time_prop(prop=random.random()),
           creator=User.objects.order_by('?').first())
reg.save()
</code>

==== Clean migrations ====
<code>
find . -path "*/migrations/*.py" -not -name "__init__.py" -delete
find . -path "*/migrations/*.pyc"  -delete
</code>

=== Script to reset the whole DB ===
<code>
#!/bin/sh

export PGPASSWORD=mysecretpassword
export DATABASE=puma

find . -path "*/migrations/*.py" -not -name "__init__.py" -delete
find . -path "*/migrations/*.pyc"  -delete

dropdb -h 127.0.0.1 -U postgres $DATABASE
createdb -T template0 -h 127.0.0.1 -U postgres $DATABASE

python manage.py makemigrations
python manage.py migrate

psql -h 127.0.0.1 -U postgres -d $DATABASE -c "INSERT INTO public.pumapp_user (password,last_login,is_superuser,username,first_name,last_name,is_staff,is_active,date_joined,email,current_project_id) VALUES ('pbkdf2_sha256$100000$8RoYX0VMbGIY$OZrZowL8A4pR/wgE/ggy7KOSAU82068MEG3tiZHV70I=',NULL,true,'admin','','',true,true,'2019-01-31 08:22:29.609','admin@a.com',NULL);"
psql -h 127.0.0.1 -U postgres -d $DATABASE -c "INSERT INTO public.redmine_auth_redmineconfig (url) VALUES ('https://redmine.gtd.es');"
</code>