【2】依照Django官网，创建一个web app 创建app/创建对应的数据库表

1. Creating app  

$ python manage.py startapp polls

       That’ll create a directory polls, which is laid out like this:

polls/    __init__.py    admin.py    migrations/        __init__.py    models.py    tests.py    views.py

1.1 Edit polls/models.py:

from django.db import modelsclass Question(models.Model):    question_text = models.CharField(max_length=200)    pub_date = models.DateTimeField('date published')    
  def __str__(self):              # __unicode__ on Python 2      return self.question_text
  def was_published_recently(self):      return self.pub_date >= timezone.now()
class Choice(models.Model):    question = models.ForeignKey(Question)    choice_text = models.CharField(max_length=200)    votes = models.IntegerField(default=0)
    def __str__(self):              # __unicode__ on Python 2
     return self.choice_text

1.2 Edit the mysite/settings.py file again, and change the INSTALLED_APPS setting to include the string 'polls':

INSTALLED_APPS = (    'django.contrib.admin',    'django.contrib.auth',    'django.contrib.contenttypes',    'django.contrib.sessions',    'django.contrib.messages',    'django.contrib.staticfiles',    'polls',)

1.3 Now Django knows to include the polls app. Let’s run another command:

$ python manage.py makemigrations polls

1.4    Now, run migrate again to create those model tables in your database:

       1.4.1   python manage.py check;

      1.4.2  python manage.py migrate

1.5    
Playing with the API
     1.5.1   python manage.py shell
     
     1.5.2   
>>> from polls.models import Question, Choice   # Import the model classes we just wrote.# No questions are in the system yet.>>> Question.objects.all()[]# 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. Note that this might say "1L" instead of "1", depending# on which database you're using. That's no biggie; it just means your# database backend prefers to return integers as Python long integer# objects.>>> q.id1# Access model field values via Python attributes.>>> q.question_text"What's new?">>> q.pub_datedatetime.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()[<Question: Question object>]
>>> from polls.models import Question, Choice# Make sure our __str__() addition worked.>>> Question.objects.all()[<Question: What's up?>]# Django provides a rich database lookup API that's entirely driven by# keyword arguments.>>> Question.objects.filter(id=1)[<Question: What's up?>]>>> Question.objects.filter(question_text__startswith='What')[<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()[]# 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()[<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)[<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()