Django使用Python操作数据库 --Django 1.8.2 文档（中文）部分笔记

原文网址
http://python.usyiyi.cn/django/intro/tutorial01.html
最好看过原文再阅读
model创建大致如下

#encoding=utf-8
from __future__ import unicode_literalsfrom django.db import models
from django.utils import timezone
import datetime class Question(models.Model):question_text = models.CharField(max_length=200)pub_date = models.DateTimeField('date published')def __str__(self):              # __unicode__ on Python 2return self.question_textdef was_published_recently(self):return self.pub_date >= timezone.now() - datetime.timedelta(days=1)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 2return self.choice_text     #the usage of this function:不仅会使你自己在使用交互式命令行时看得更加方便，而且会在Django自动生成的管理界面中使用对象的这种表示# three step of change models
# 1.修改你的模型（在models.py文件中）。
# 2.运行python manage.py makemigrations ，为这些修改创建迁移文件
# 3.运行python manage.py migrate ，将这些改变更新到数据库中。

使用python manage.py shell进行数据库操作

#encoding=utf-8
>>> from polls.models import Question, Choice   # Import the model classes we just wrote.# No questions are in the system yet.
#选择所有的Question
>>> 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
#创建一个question对象
>>> q = Question(question_text="What's new?", pub_date=timezone.now())# Save the object into the database. You have to call save() explicitly.
#保存
>>> 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.
#获取Question的一些属性
>>> 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>)#修改属性并保存
# Change values by changing the attributes, then calling save().
>>> q.question_text = "What's up?"
>>> q.save()#再次查询所有Question
# objects.all() displays all the questions in the database.
>>> Question.objects.all()
[<Question: Question object>]#=======================================================================>>> from polls.models import Question, Choice# 添加__str__()方法后再次查询所有Question
# Make sure our __str__() addition worked.
>>> Question.objects.all()
[<Question: What's up?>]# 使用过滤器查询
# 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.# pk应该就是primary key的意思？
# 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（构建） a new
# Choice object, does the INSERT statement（陈述，声明）, 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)# 通过相关的Question对象显示与其有关的Choice对象集合---目前还没有相关的Choice对象
# Display any choices from the related object set -- none so far.
>>> q.choice_set.all()
[]# 使用Question对象的Choice集合创建Choice对象
# 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对象也有一些API来访问与其相关的Question对象
# Choice objects have API access to their related Question objects.
>>> c.question
<Question: What's up?># 而反之亦然
# 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# 查询一些Choice对象，这些Choice对象所属的Question对象的pub_date的年份为系统当前年份# 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>]# 通过Question对象查询出Choice对象，删除
# Let's delete one of the choices. Use delete() for that.
>>> c = q.choice_set.filter(choice_text__startswith='Just hacking')
>>> c.delete()

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