Django Models§

Storing and manipulating data with the Django ORM.

Configuring Databases

          DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',  # 'postgresql_psycopg2', 'mysql', 'sqlite3' or 'oracle'.
        'NAME': 'address.db',
        'USER': '',                      # Not used with sqlite3.
        'PASSWORD': '',                  # Not used with sqlite3.
        'HOST': '',                      # Set to empty string for localhost. Not used with sqlite3.
        'PORT': '',                      # Set to empty string for default. Not used with sqlite3.
    }
}

        

Defining Models

Models are created in the models module of a Django app and subclass Model

          from django.db import models

class Contact(models.Model):

    first_name = models.CharField(
        max_length=255,
    )
    last_name = models.CharField(
        max_length=255,

    )

    email = models.EmailField()

Instantiating Models

          nathan = Contact()
nathan.first_name = 'Nathan'
nathan.last_name = 'Yergler'
nathan.save()

        

          nathan = Contact.objects.create(
    first_name='Nathan',
    last_name='Yergler')

        

          nathan = Contact(
    first_name='Nathan',
    last_name='Yergler')
nathan.save()

        

Model Managers

A model instance maps to a row
The model Manager maps to the table
Every model has a default manager, objects
Operations that deal with more than one instance, or at the "collection" level, usually map to the Manager

Querying with Managers

The filter Manager method lets you perform queries:
```
Contact.objects.filter(last_name='Yergler')
```
filter returns a QuerySet, an iterable over the result.

You can also assert you only expect one:

              Contact.objects.get(first_name='Nathan')

            

If more than one is returned, an Exception will be raised
The full query reference is pretty good on this topic.

Testing Models

Business logic is usually added as methods on a Model.
Important to write unit tests for those methods as you add them.
We'll write an example test for the methods we add.

Running the Tests

You can run the tests for your application using manage.py:

(tutorial)$ python manage.py test

Review§

Models define the fields in a table, and can contain business logic.
The syncdb manage command creates the tables in your database from models
The model Manager allows you to operate on the collection of instances: querying, creating, etc.
Write unit tests for methods you add to the model
The test manage command runs the unit tests

Next: Writing Views