Models Django

DataBase Connection

At "crud/settings.py" you can set the DataBase Connection, the following is an example for PostgreSQL:

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql',
        'NAME': 'mydatabase',
        'USER': 'mydatabaseuser',
        'PASSWORD': 'mypassword',
        'HOST': '127.0.0.1',
        'PORT': '5432',
    }
}

Examples for ENGINE values according to the DBMS:

SQLite3: 'django.db.backends.sqlite3'
PostgreSQL: 'django.db.backends.postgresql'
MySQL/MariaDB: 'django.db.backends.mysql'
Oracle: 'django.db.backends.oracle'

In this case you must set the next values for using MariaDB running on localhost:3306 with a DataBase called "django":

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'django',
        'USER': 'root',
        'PASSWORD': '',
        'HOST': 'localhost',
        'PORT': '3306',
    }
}

It is important to install the driver according to the DBMS, in this example we are going to use MySQL, then we must install "mysqlclient" driver:

(env) path-to-the-project/my_project>pip install mysqlclient

Finally, the following command will execute the changes in the DataBase:

(env) path-to-the-project/my_project>python manage.py migrate

Create Models

All my_app's models will be in a unique file: "my_app/models.py":

from django.db import models

class Role(models.Model):
    role = models.CharField(max_length=255)

class User(models.Model):
    id = models.AutoField(primary_key=True)
    name = models.CharField(max_length=255)
    username = models.CharField(max_length=255)
    birthday = models.DateField()
    role = models.ForeignKey(Role, on_delete=models.CASCADE)
    active = models.BooleanField(default=True)

Django creates the entities in the DataBase according to the declared Models

Finally, you must use three commands:

1. For indicating there are changes in the my_app model and must be apply on migrations:

(env) path-to-the-project/my_project>py manage.py makemigrations my_app

The termial answer this:

Migrations for 'my_app':
    my_app\migrations\0001_initial.py
      - Create model Role
      - Create model User

2. For whatching the SQL changes taht will be executed:

(env) path-to-the-project/my_project>py manage.py sqlmigrate my_app 0001

The terminal answer:

--
-- Create model Role
--
CREATE TABLE `my_app_role` (`id` bigint AUTO_INCREMENT NOT NULL PRIMARY KEY, `role` varchar(255) NOT NULL);
--
-- Create model User
--
CREATE TABLE `my_app_user` (`id` integer AUTO_INCREMENT NOT NULL PRIMARY KEY, `name` varchar(255) NOT NULL, `username` varchar(255) NOT NULL, `birthday` date NOT NULL, `active` bool NOT NULL, `role_id` bigint NOT NULL);
ALTER TABLE `my_app_user` ADD CONSTRAINT `my_app_user_role_id_d87f73e6_fk_my_app_role_id` FOREIGN KEY (`role_id`) REFERENCES `my_app_role` (`id`);

3. For executing the migration in the DataBase:

(env) path-to-the-project/my_project>py manage.py migrate

Now, the new tables according to the models, should be created.

Before finish this post, I would like to show a couple of queries done to ChatGPT while I make this article:

Django Data types

1. AutoField: IntegerField that automatically increments.

2. BigAutoField: BigIntegerField that automatically increments.

3. BinaryField: Binary data, up to 2^31 - 1 bytes.

4. BooleanField: Boolean (True/False) value.

5. CharField: Character string of a fixed length.

6. DateField: Date (year, month, day).

7. DateTimeField: Date and time.

8. DecimalField: Fixed-point decimal numbers.

9. DurationField: Time duration.

10. EmailField: Email address.

11. FileField: File path.

12. FilePathField: File path from a set of choices.

13. FloatField: Floating-point number.

14. ImageField: Image path.

15. IntegerField: Integer value.

16. GenericIPAddressField: IPv4 or IPv6 address.

17. NullBooleanField: Like a BooleanField, but allows NULL values.

18. PositiveIntegerField: Integer value greater than or equal to zero. 19. PositiveSmallIntegerField: Integer value greater than or equal to zero and less than 32768.

20. SlugField: Short label for URL use, containing only letters, numbers, hyphens or underscores.

21. SmallAutoField: SmallIntegerField that automatically increments.

22. SmallIntegerField: Integer value between -32768 and 32767.

23. TextField: Text of arbitrary length.

24. TimeField: Time of day.

25. URLField: URL.

Attributes

1. null: If True, Django will store empty values as NULL in the database. Default is False.

2. blank: If True, the field is allowed to be blank. Default is False.

3. choices: A sequence of 2-tuples where the first element is the value to be stored in the database and the second element is the human-readable name. Can be used to create drop-down select boxes in forms.

4. default: The default value for the field. Can be a value or a callable.

5. editable: If False, the field will not be displayed in the admin or any ModelForm. Default is True.

6. help_text: Extra "help" text to be displayed alongside the field in forms.

7. primary_key: If True, the field is the primary key for the model. Only one field in a model can have this attribute set to True.

8. unique: If True, the field must be unique throughout the table. Default is False.

9. verbose_name: A human-readable name for the field, used in the admin and other places where the field is displayed.

An example Model

This is a model declaration which uses the most common data types and attributes for holding like an example:

from django.db import models

class ExampleModel(models.Model):
    name = models.CharField(max_length=100, unique=True, help_text='Enter the name of the object')
    description = models.TextField(blank=True, help_text='Enter a brief description of the object')
    is_active = models.BooleanField(default=True, help_text='Is this object currently active?')
    timestamp = models.DateTimeField(auto_now_add=True, help_text='Date and time the object was created')
    rating = models.DecimalField(max_digits=5, decimal_places=2, null=True, blank=True, help_text='The rating of the object')
    image = models.ImageField(upload_to='images/', null=True, blank=True, help_text='Upload an image of the object')

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