Models and the admin site

1. Database setup

   $ pip install mysqlclient
   

2. Creating models

   from django.db import models
   
   class Question(models.Model):
       question_text = models.CharField(max_length=200)
       pub_date = models.DateTimeField('date published')
   
   class Choice(models.Model):
       question = models.ForeignKey(Question, on_delete=models.CASCADE)
       choice_text = models.CharField(max_length=200)
       votes = models.IntegerField(default=0)
   

3. Include the app in our project

   INSTALLED_APPS = [
       'polls.apps.PollsConfig',
       'django.contrib.admin',
       'django.contrib.auth',
       'django.contrib.contenttypes',
       'django.contrib.sessions',
       'django.contrib.messages',
       'django.contrib.staticfiles',
   ]
   

4. Activating models

   # 生成迁移文件
   $ python manage.py makemigrations polls
   # 执行指定迁移
   $ python manage.py migrate polls 0001
   # 执行全部迁移
   $ python manage.py migrate
   

5. Playing with the API

   # 进入Database API
   $ python manage.py shell
   

   # Import the model classes we just wrote.
   >>> from polls.models import Choice, Question  
   
   # No questions are in the system yet.
   >>> Question.objects.all()
   <QuerySet []>
   
   # Create a new Question.
   # Support for time zones is enabled in the default settings file, so
   # Django expects a datetime with tzinfo for pub_date. Use timezone.now()
   # instead of datetime.datetime.now() and it will do the right thing.
   >>> from django.utils import timezone
   >>> q = Question(question_text="What's new?", pub_date=timezone.now())
   
   # Save the object into the database. You have to call save() explicitly.
   >>> q.save()
   
   # Now it has an ID.
   >>> q.id
   1
   
   # Access model field values via Python attributes.
   >>> q.question_text
   "What's new?"
   >>> q.pub_date
   datetime.datetime(2012, 2, 26, 13, 0, 0, 775217, tzinfo=<UTC>)
   
   # Change values by changing the attributes, then calling save().
   >>> q.question_text = "What's up?"
   >>> q.save()
   
   # objects.all() displays all the questions in the database.
   >>> Question.objects.all()
   <QuerySet [<Question: Question object (1)>]>
   

   # 通过给polls/models.py 中的模型添加__str__()方法
   # 让Question.objects.all()的调用显示对于的值
   from django.db import models
   
   class Question(models.Model):
       # ...
       def __str__(self):
           return self.question_text
   
   class Choice(models.Model):
       # ...
       def __str__(self):
           return self.choice_text
   

   >>> from polls.models import Choice, Question
   
   # Make sure our __str__() addition worked.
   >>> Question.objects.all()
   <QuerySet [<Question: What's up?>]>
   
   # Django provides a rich database lookup API that's entirely driven by
   # keyword arguments.
   >>> Question.objects.filter(id=1)
   <QuerySet [<Question: What's up?>]>
   >>> Question.objects.filter(question_text__startswith='What')
   <QuerySet [<Question: What's up?>]>
   
   # Get the question that was published this year.
   >>> from django.utils import timezone
   >>> current_year = timezone.now().year
   >>> Question.objects.get(pub_date__year=current_year)
   <Question: What's up?>
   
   # Request an ID that doesn't exist, this will raise an exception.
   >>> Question.objects.get(id=2)
   Traceback (most recent call last):
       ...
   DoesNotExist: Question matching query does not exist.
   
   # Lookup by a primary key is the most common case, so Django provides a
   # shortcut for primary-key exact lookups.
   # The following is identical to Question.objects.get(id=1).
   >>> Question.objects.get(pk=1)
   <Question: What's up?>
   
   # Make sure our custom method worked.
   >>> q = Question.objects.get(pk=1)
   >>> q.was_published_recently()
   True
   
   # Give the Question a couple of Choices. The create call constructs a new
   # Choice object, does the INSERT statement, adds the choice to the set
   # of available choices and returns the new Choice object. Django creates
   # a set to hold the "other side" of a ForeignKey relation
   # (e.g. a question's choice) which can be accessed via the API.
   >>> q = Question.objects.get(pk=1)
   
   # Display any choices from the related object set -- none so far.
   >>> q.choice_set.all()
   <QuerySet []>
   
   # Create three choices.
   >>> q.choice_set.create(choice_text='Not much', votes=0)
   <Choice: Not much>
   >>> q.choice_set.create(choice_text='The sky', votes=0)
   <Choice: The sky>
   >>> c = q.choice_set.create(choice_text='Just hacking again', votes=0)
   
   # Choice objects have API access to their related Question objects.
   >>> c.question
   <Question: What's up?>
   
   # And vice versa: Question objects get access to Choice objects.
   >>> q.choice_set.all()
   <QuerySet [<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]>
   >>> q.choice_set.count()
   3
   
   # The API automatically follows relationships as far as you need.
   # Use double underscores to separate relationships.
   # This works as many levels deep as you want; there's no limit.
   # Find all Choices for any question whose pub_date is in this year
   # (reusing the 'current_year' variable we created above).
   >>> Choice.objects.filter(question__pub_date__year=current_year)
   <QuerySet [<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]>
   
   # Let's delete one of the choices. Use delete() for that.
   >>> c = q.choice_set.filter(choice_text__startswith='Just hacking')
   >>> c.delete()
   

6. Creating an admin user

   $ python manage.py createsuperuser
   Username: admin
   Email address: admin@example.com
   Password: **********
   Password (again): *********
   Superuser created successfully.
   

7. Make the poll app modifiable in the admin

   # polls/admin.py
   from django.contrib import admin
   from .models import Question
   
   admin.site.register(Question)