Django Tutorial

Designing the LocalLibrary models

• When designing your models it makes sense to have separate models for every “object” (a group of related information). In this case, the obvious objects are books, book instances, and authors.

• We might need to store more information about the author than just their name, and there might be multiple authors with the same or similar names. We want to be able to sort information based on book title, author, written language, and category.

Model definition

• Models are usually defined in an application’s models.py file. They are implemented as subclasses of django.db.models.Model, and can include fields, methods and metadata. The code fragment below shows a “typical” model, named MyModelName:

from django.db import models

class MyModelName(models.Model):
    """A typical class defining a model, derived from the Model class."""

    # Fields
    my_field_name = models.CharField(max_length=20, help_text='Enter field documentation')
    ...

    # Metadata
    class Meta:
        ordering = ['-my_field_name']

    # Methods
    def get_absolute_url(self):
        """Returns the url to access a particular instance of MyModelName."""
        return reverse('model-detail-view', args=[str(self.id)])

    def __str__(self):
        """String for representing the MyModelName object (in Admin site etc.)."""
        return self.my_field_name

Fields

• A model can have an arbitrary number of fields, of any type — each one represents a column of data that we want to store in one of our database tables. Each database record (row) will consist of one of each field value. Let’s look at the example seen below:

my_field_name = models.CharField(max_length=20, help_text='Enter field documentation')

Common field arguments

• The following common arguments can be used when declaring many/most of the different field types:

1) help_text 2) verbose_name 3) default 4) null 5) blank 6) choices 7) primary_key

Common field types

The following list describes some of the more commonly used types of fields.

1) CharField 2) TextField. 3) IntegerField 4) DateField 5) EmailField 6) FileField 7) AutoField 8) ManyToManyField

Advanced configuration

• Django does a pretty good job of creating a basic admin site using the information from the registered models:

Each model has a list of individual records, identified by the string created with the model’s str() method, and linked to detail views/forms for editing. By default, this view has an action menu at the top that you can use to perform bulk delete operations on records. The model detail record forms for editing and adding records contain all the fields in the model, laid out vertically in their declaration order.