[PYTHON] [Day 9] Creating a model

January 14, 2021 ← Last time: Display template in Day 8 Template View

Precautionary statement

This article is not a single article. I wrote it as a diary, so I think it will be useful for those who are new to it. If you want to learn Django, we recommend reading it from [Day 1] Django Development Environment.

Introduction

The theme this time is "Creating a model". So far, it's very rudimentary, but we've looked at View and Template. The rest is Model. Django has a mechanism that allows you to link with a database and perform validation processing smartly by giving various information to the model. This time, let's make a simple model and learn because it is a bulletin board.

Add thread application

First, create a thread application. This is an application that handles things related to bulletin board threads.

(venv)$ ./manage.py startapp thread

Add thread/urls.py, add application to mysite/settings.py, and add URL to mysite/urls.py as well as base application. This area is similar to the base application. [Day 4] Application Creation For reference

mysite/settings.py

  INSTALLED_APPS = [
      'django.contrib.admin',
      'django.contrib.auth',
      'django.contrib.contenttypes',
      'django.contrib.sessions',
      'django.contrib.messages',
      'django.contrib.staticfiles',
      'django.contrib.sites',
      'django.contrib.sitemaps',
      'debug_toolbar',
      'base',
+     'thread',
  ]

mysite/urls.py

  urlpatterns = [
      path('admin/', admin.site.urls),
      path('', include('base.urls')),
+     path('thread/', include('thread.urls')),
  ]

thread/urls.py

from django.urls import path

from . import views
app_name = 'thread'

urlpatterns = [
]

Now the additional processing of the application is OK.

Model addition

The thread application model is assumed to be as follows. First, consider the following model so that it has the minimum functions of the bulletin board.

thread/models.py

from django.db import models

class TopicManager(models.Manager):
    #Added processing related to Topic operation
    pass

class CommentManager(models.Manager):
    #Added processing related to Comment operation
    pass

class CategoryManager(models.Manager):
    #Added processing related to Category operation
    pass

class Category(models.Model):
    name = models.CharField(
        'Category name',
        max_length=50,
    )
    url_code = models.CharField(
        'URL code',
        max_length=50,
        null=True,
        blank=False,
        unique=True,
    )
    sort=models.IntegerField(
        verbose_name='sort',
        default=0,
    )
    objects = CategoryManager

    def __str__(self):
        return self.name

class Topic(models.Model):
    user_name = models.CharField(
        'name',
        max_length=30,
        null=True,
        blank=False,
    )
    title = models.CharField(
        'title',
        max_length=255,
        null = False,
        blank = False,
    )
    message = models.TextField(
        verbose_name='Text',
        null=True,
        blank=False,
    )
    category = models.ForeignKey(
        Category,
        verbose_name='Category',
        on_delete=models.PROTECT,
        null=True,
        blank=False,
    )
    created = models.DateTimeField(
        auto_now_add=True,
    )
    modified = models.DateTimeField(
        auto_now=True,
    )
    objects = TopicManager()

    def __str__(self):
        return self.title

class Comment(models.Model):
    id = models.BigAutoField(
        primary_key=True,
    )
    no = models.IntegerField(
        default=0,
    )
    user_name = models.CharField(
        'name',
        max_length=30,
        null=True,
        blank=False,
    )
    topic = models.ForeignKey(
        Topic,
        on_delete=models.PROTECT,
    )
    message = models.TextField(
        verbose_name='Posted content'
    )
    pub_flg = models.BooleanField(
        default=True,
    )
    created = models.DateTimeField(
        auto_now_add=True,
    )
    objects = CommentManager()

    def __str__(self):
        return '{}-{}'.format(self.topic.id, self.no)

Brief commentary

From here, we will enter the above (thread/models.py) explanation. Therefore, I will post the URL of the head family. Honke After that, I will put the explanation below so that you do not have to jump to the link, but since it is exactly the same as the head family, it is recommended to fly to the head family and refer to it.

Model field

null and blank

Automatic ID generation

Foreign key

models.CASCADE: Models referenced along with foreign key models are also deleted models.PROTECT: Protected (cannot be deleted if referenced) models.SET_NULL: ID will be NULL if the foreign key model is deleted models.SET_DEFAULT: The value set by default is set. Is PROTECT recommended? CASCADE is a little risky, but I don't think it's a problem depending on the design.

About the manager

See you again

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