Data model class

Write data model

• The following code demonstrates the class that defines a blog post in models.py

from django.db import models
from django.utils import timezone
from django.contrib.auth.models import User


# Create your models here.
class BlogArticles(models.Model):  # The data model classes in Django are all inherited from the django.db.models.Model class.
    # The property of field title is of type CharField and the parameter length is 300
    title = models.CharField(max_length=300)
    """
    //Field author uses ForeignKey to define the relationship between blog posts and users: one user corresponds to multiple posts
    models.CASCADE Indicates cascade deletion
    related_name="blog_posts" Express permission User Class to "blog_posts" Property reverse query to BlogArticles Class instances
    """
    author = models.ForeignKey(User, on_delete=models.CASCADE, related_name="blog_posts")
    body = models.TextField()
    publish = models.DateTimeField(default=timezone.now)

    """
    ordering = ("-publish",) Regulations BlogArticles Class by publish Display field values in reverse order
    """
    class Meta:
        ordering = ("-publish",)

    """
    //Override the method of the parent class to return the value of the title property when the str() function is used to convert an instance of the class to a string
    """
    def __str__(self):
        return self.title

Building database table based on data model

1. Create database table file

E:\PycharmProjects\demosite>python manage.py makemigrations
Migrations for 'blog':
  blog\migrations\0002_auto_20190720_1919.py
    - Alter field publish on blogarticles

1. In the above prompt for execution results, we are told that a BlogArticles model with model number 0001 has been created in the blog/migrations directory. You can enter the following command to view the corresponding SQL statement:

E:\PycharmProjects\demosite>python manage.py sqlmigrate blog 0001
System check identified some issues:

WARNINGS:
blog.BlogArticles.publish: (fields.W161) Fixed default value provided.
        HINT: It seems you set a fixed date / time / datetime value as default for this field. This may not be what you want. If you want to have the current date as default, use `django.utils.timezone.now`
BEGIN;
--
-- Create model BlogArticles
--
CREATE TABLE "blog_blogarticles" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "title" varchar(300) NOT NULL, "body" text NOT NULL, "publish" datetime NOT NULL, "author_id" integer NOT NULL REFERENCES "auth_user" ("id") DEFERRABLE INITIALLY DEFERRED);
CREATE INDEX "blog_blogarticles_author_id_ed798e23" ON "blog_blogarticles" ("author_id");
COMMIT;

1. Create database

(demosite) E:\PycharmProjects\demosite>python manage.py migrate
System check identified some issues:

WARNINGS:
blog.BlogArticles.publish: (fields.W161) Fixed default value provided.
        HINT: It seems you set a fixed date / time / datetime value as default for this field. This may not be what you want. If you want to have the current date as default, use `django.utils.timezone.now`
Operations to perform:
  Apply all migrations: admin, auth, blog, 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 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 auth.0010_alter_group_name_max_length... OK
  Applying auth.0011_update_proxy_permissions... OK
  Applying blog.0001_initial... OK
  Applying sessions.0001_initial... OK