Django: Model

• 1, Configuring the Database

in settings.py

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': os.path.join(BASE_DIR, 'db.sqlite3'),
    }
}

• 2, Create a books app

python manage.py startapp books 

and then the layout of dir.

\mypro
    \books
        \migrations
          __init__.py
        admin.py
        apps.py
        models.py
        tests.py
        views.py
    \mypro
    \templates
    manage.py

• 3, Define Models

in models.py

from django.db import models

class Publisher(models.Model):
    name = models.CharField(max_length=30)
    address = models.CharField(max_length=50)
    city = models.CharField(max_length=60)
    state_province = models.CharField(max_length=30)
    country = models.CharField(max_length=50)
    website = models.URLField()

class Author(models.Model):
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=40)
    email = models.EmailField()

class Book(models.Model):
    title = models.CharField(max_length=100)
    authors = models.ManyToManyField(Author)
    publisher = models.ForeignKey(Publisher)
    publication_date = models.DateField()

• 4, Install Models

in settings.py

INSTALLED_APPS = [
'books.apps.BooksConfig',      # add this line
'django.contrib.admin',
'django.contrib.auth',
'django.contrib.contenttypes',
'django.contrib.sessions',
'django.contrib.messages',
'django.contrib.staticfiles',
]

BooksConfig class that Django created for you in the apps.py file.

• 5, validate the models

python manage.py check 

If it's succeed, it would output

System check identified no issues (0 silenced).

• 6, Migrate database

When running

python manage.py makemigrations books 

it outputs

Migrations for 'books':
  0001_initial.py:
    - Create model Author
    - Create model Book
    - Create model Publisher
    - Add field publisher to book 

Running

python manage.py sqlmigrate books 0001

it would output

BEGIN;

CREATE TABLE "books_author" (
    "id" integer NOT NULL PRIMARY KEY AUTOINCREMENT,
    "first_name" varchar(30) NOT NULL,
    "last_name" varchar(40) NOT NULL,
    "email" varchar(254) NOT NULL
);
CREATE TABLE "books_book" (
    "id" integer NOT NULL PRIMARY KEY AUTOINCREMENT,
    "title" varchar(100) NOT NULL,
    "publication_date" date NOT NULL
);
CREATE TABLE "books_book_authors" (
    "id" integer NOT NULL PRIMARY KEY AUTOINCREMENT,
    "book_id" integer NOT NULL REFERENCES "books_book" ("id"),
    "author_id" integer NOT NULL REFERENCES "books_author" ("id"),
    UNIQUE ("book_id", "author_id")
);
CREATE TABLE "books_publisher" (
    "id" integer NOT NULL PRIMARY KEY AUTOINCREMENT,
    "name" varchar(30) NOT NULL,
    "address" varchar(50) NOT NULL,
    "city" varchar(60) NOT NULL,
    "state_province" varchar(30) NOT NULL,
    "country" varchar(50) NOT NULL,
    "website" varchar(200) NOT NULL
);
CREATE TABLE "books_book__new" (
    "id" integer NOT NULL PRIMARY KEY AUTOINCREMENT,
    "title" varchar(100) NOT NULL,
    "publication_date" date NOT NULL,
    "publisher_id" integer NOT NULL REFERENCES
    "books_publisher" ("id")
);

INSERT INTO "books_book__new" ("id", "publisher_id", "title",
"publication_date") SELECT "id", NULL, "title", "publication_date" FROM
"books_book";

DROP TABLE "books_book";

ALTER TABLE "books_book__new" RENAME TO "books_book";

CREATE INDEX "books_book_2604cbea" ON "books_book" ("publisher_id");

COMMIT;

Django provides an easier way of committing the SQL to the database: the migrate command:

python manage.py migrate 

then u'll see things like,

Operations to perform:
Apply all migrations: admin, auth, books, contenttypes, sessions
Running migrations:
Applying books.0001_initial... OK

read more

• The django Book: Django Models

• The django Book: Django Models: Basic Data Access

• The django Book: Database API Reference