03 - Django 定义模型

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作者： 张启卫
时间： 2017年4月13号
功能：

• 使用Django创建表
• 理解模型的概念

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03 - 数据库设置

打开mysite/settings.py

python manage.py migrate  #installed_APPs

设置数据库
设置Time-zone

第二步：定义models

myblog/polls/models.py

from django.db import models

# Create your models here.

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)

learnning-log/learnning-logs/models.py

from django.db import models

# Create your models here.
# 创建一个Topic的类
# 包含text 与 date_added属性
# 包含__str__方法，返回text中字符串

class Topic(models.Model):
    """用户学习的主题"""
    text = models.CharField(max_length=200)
    date_added = models.DateTimeField(auto_now_add=True)

    def __str__(self):
        """返回模型的字符串表示"""
        return self.text

第三步： 激活模型

mysite/settings.py

# Application definition
    # 这是一个元组，告诉Django项目是由哪些应用程序组成的

INSTALLED_APPS = (
    ‘django.contrib.admin’,
    ‘django.contrib.auth’,
    ‘django.contrib.contenttypes’,
    ‘django.contrib.sessions’,
    ‘django.contrib.messages’,
    ‘django.contrib.staticfiles’,
    ‘blog’,
    ‘polls.apps.PollsConfig’,
        ‘learning_logs’
)

#修改数据库Polls
python manage.py makemigrations polls

    #查看sql语句
python manage.py sqlmigrate polls 0001

    #检查
python manage.py check

    # 让项目迁移
python manage.py migrate

(ll_env) David@10:~/02_project/learning-log$ python manage.py makemigrations learning_logs
Migrations for 'learning_logs':
  learning_logs/migrations/0001_initial.py
- Create model Topic

(ll_env) David@10:~/02_project/learning-log$ python manage.py migrate
Operations to perform:
  Apply all migrations: admin, auth, contenttypes, learning_logs, sessions
Running migrations:
  Applying learning_logs.0001_initial... OK

小结：
修改数据库步骤：
第一步：定义models
第二步: python manage.py makemigrations
第三步： python manage.py migrate

python manage.py shell
or
python
import django
django.setup()

	>>> from polls.models import Question, Choice   # Import the model classes we just wrote.

# 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. 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.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>]>

Django 管理员

第一步：创建一个管理员用户

python manage.py createsuperuser

http://127.0.0.1:8000/admin

第二步：让app在admin管理中可用

polls/admin.py
from django.contrib import admin
from .models import Question

# Register your models here.
admin.site.register(Question)

理解模型的概念

每一个模型都是django.db.models.Model的子类
每个属性都表示数据库的一个字段