这里model可以认为是数据对象本身

相当于在写java代码时候model目录下创建的实体类，models.py 中可以包含多个实体类，感觉这个操作挺骚的

下面是polls app里面的models，仍然根据刘江老师的网站进行学习，此处不赘述。

models.py

from django.db import models# Create your models here.from django.db import modelsclass 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)

这里的Question 和 Choice 两个类，将来在mysql之中就是两张表，就叫这俩名字！而类中的属性就是字段名即column名

完事之后，请将polls加在settings.py中的INSTALLED_APP列表中，准备迁移。

直接用简写方式就行：

下面在settings.py中

# pysite/settings.pyINSTALLED_APPS = ['polls','django.contrib.admin','django.contrib.auth','django.contrib.contenttypes','django.contrib.sessions','django.contrib.messages','django.contrib.staticfiles',]

好的开始迁移，之前做的迁移是对项目整体迁移，当model有所更新的时候，新的内容需要再次同步

终端运行：

python manage.py makemigrations polls

这时候得到如下提示：

Migrations for 'polls':  polls/migrations/0001_initial.py:    - Create model Choice    - Create model Question

django获得了迁移信息，然后迁移：

python manage.py migrate

看到这样的画面：

python manage.py migrateOperations to perform:    Apply all migrations: admin, auth, contenttypes, polls, sessionsRunning migrations:    Rendering model states... DONE    Applying polls.0001_initial... OK

这样来到数据库后，你就发现多了些东西

两张表后缀名是不是似曾相识呢？

没错就是想的那样。

接下来打开进入交互界面中（在终端中）：

import django

django.setup()

接下来这段直接拿刘老师写的内容加一些自己的理解粘过来：

>>> from polls.models import Question, Choice # 导入我们写的模型类    # 现在系统内还没有questions对象    >>> Question.objects.all()    
     
          # 创建一个新的question对象    # Django推荐使用timezone.now()代替python内置的datetime.datetime.now()    # 这个timezone就来自于Django的依赖库pytz    from django.utils import timezone    >>> q = Question(question_text="What's new?", pub_date=timezone.now())    # 你必须显式的调用save()方法，才能将对象保存到数据库内    >>> q.save()    # 默认情况，你会自动获得一个自增的名为id的主键    >>> q.id    1    # 通过python的属性调用方式，访问模型字段的值    >>> q.question_text    "What's new?"    >>> q.pub_date    datetime.datetime(2012, 2, 26, 13, 0, 0, 775217, tzinfo=
      
       )    # 通过修改属性来修改字段的值，然后显式的调用save方法进行保存。 　　#这里请注意，这种写法实际上是不安全的，因为你不会允许其他人随意更改一个类的属性值，后续应该在models里面将实体类的属性私有化而不是直接这样放，使用get，set方法获取和修改     >>> q.question_text = "What's up?"    >>> q.save()    # objects.all() 用于查询数据库内的所有questions    >>> Question.objects.all()    
       
        ]>
       
      
     

当调用了q.save()之后，来到你的数据库中，这里q是一个Question对象，对应的表polls_question中你会发现表里面多了一条数据，就是你刚才写的。

django在创建表之初会自动创建id主键自增列，所以调用增删改查就不用过多考虑，你默认它（id）存在即可。

对models进行小修改：

models.py

from django.db import modelsimport datetimefrom django.utils import timezone# Create your models here.from django.db import modelsclass Question(models.Model):    question_text = models.CharField(max_length=200)    pub_date = models.DateTimeField('date published')    #toString()方法    def __str__(self):        return self.question_text    def was_published_recently(self):        return self.pub_date >= timezone.now() - datetime.timedelta(days=1)class Choice(models.Model):    question = models.ForeignKey(Question,on_delete=models.CASCADE)    choice_text = models.CharField(max_length=200)    votes = models.IntegerField(default=0)    def __str__(self):        return self.choice_text

然后你重启shell，这时候

>>> import django>>> django.setup()>>> from polls.models import Question, Choice>>> Question.objects.all()
     
      ]>
     

，今天上课先写这些喽，继续学习新知识！！

于是我又回来了

使用其它api

Question.objects.filter(question_text__startswith='What')

 

这里是区分大小写的，What !=what

(venv) D:\pysite>python manage.py shell Python 3.6.2 (v3.6.2:5fd33b5, Jul  8 2017, 04:57:36) [MSC v.1900 64 bit (AMD64)] on win32 Type "help", "copyright", "credits" or "license" for more information. (InteractiveConsole) >>> >>> >>> from polls.models import Question, Choice >>> Question.objects.all() 
     
      ]> >>> Question.objects.filter(id=1) 
      
       ]> >>> Question.objects.filter(question_text__startswith='What') 
       
         >>> Question.objects.filter(question_text__startswith='What') 
        
          >>> Question.objects.filter(question_text__startswith="What's") 
         
           >>> Question.objects.filter(question_text__startswith='what') 
          
           ]> >>> from django.utils import timezone File "
           
            ", line 1 from django.utils import timezone ^ IndentationError: unexpected indent >>> from django.utils import timezone >>> current_year = timezone.now().year >>> Question.objects.get(pub_date__year=current_year) 
            
              >>> Question.objects.get(id=2) Traceback (most recent call last): File "
             
              ", line 1, in 
              
                File "D:\pysite\mysite\venv\lib\site-packages\django\db\models\manager.py", line 82, in manager_metho d return getattr(self.get_queryset(), name)(*args, **kwargs) File "D:\pysite\mysite\venv\lib\site-packages\django\db\models\query.py", line 408, in get self.model._meta.object_name polls.models.Question.DoesNotExist: Question matching query does not exist. >>> Question.objects.get(pk=1) 
               
                 >>> q = Question.objects.get(pk=1) >>> q.was_published_recently() True >>> q.choice_set.all() 
                
                  >>> q.choice_set.create(choice_text='Not much',votes=0) 
                 
                   >>> q.choice_set.create(choice_text='The sky',votes=0) 
                  
                    >>> c = q.choice_set.create(choice_text='Just hacking again',votes=0) >>> c.question 
                   
                     >>> q.choice_set.all() 
                    
                     , 
                     
                      , 
                      
                       ]> >>> q.choice_count() Traceback (most recent call last): File "
                       
                        ", line 1, in 
                        
                          AttributeError: 'Question' object has no attribute 'choice_count' >>> q.choice_set.count() 3 >>> Choice.objects.filter(question__pub_date__year=current_year) 
                         
                          , 
                          
                           , 
                           
                            ]> >>> c = q.choice_set.filter(choice_text__startwith'Just hacking') File "
                            
                             ", line 1 c = q.choice_set.filter(choice_text__startwith'Just hacking') ^ SyntaxError: invalid syntax >>> c = q.choice_set.filter(choice_text__startwith='Just hacking') Traceback (most recent call last): File "
                             
                              ", line 1, in 
                              
                                File "D:\pysite\mysite\venv\lib\site-packages\django\db\models\manager.py", line 82, in manager_metho d return getattr(self.get_queryset(), name)(*args, **kwargs) File "D:\pysite\mysite\venv\lib\site-packages\django\db\models\query.py", line 892, in filter return self._filter_or_exclude(False, *args, **kwargs) File "D:\pysite\mysite\venv\lib\site-packages\django\db\models\query.py", line 910, in _filter_or_exc lude clone.query.add_q(Q(*args, **kwargs)) File "D:\pysite\mysite\venv\lib\site-packages\django\db\models\sql\query.py", line 1290, in add_q clause, _ = self._add_q(q_object, self.used_aliases) File "D:\pysite\mysite\venv\lib\site-packages\django\db\models\sql\query.py", line 1318, in _add_q split_subq=split_subq, simple_col=simple_col, File "D:\pysite\mysite\venv\lib\site-packages\django\db\models\sql\query.py", line 1251, in build_fil ter condition = self.build_lookup(lookups, col, value) File "D:\pysite\mysite\venv\lib\site-packages\django\db\models\sql\query.py", line 1110, in build_loo kup lhs = self.try_transform(lhs, lookup_name) File "D:\pysite\mysite\venv\lib\site-packages\django\db\models\sql\query.py", line 1151, in try_trans form "permitted%s" % (name, output_field.__name__, suggestion) django.core.exceptions.FieldError: Unsupported lookup 'startwith' for CharField or join on the field no t permitted, perhaps you meant startswith or istartswith? >>> c = q.choice_set.filter(choice_text__startswith='Just hacking') >>> c.delete() (1, { 'polls.Choice': 1}) >>> c.objects.all() Traceback (most recent call last): File "
                               
                                ", line 1, in 
                                
                                  AttributeError: 'QuerySet' object has no attribute 'objects' >>> c.all() 
                                 
                                   >>> q.choice_set.all() 
                                  
                                   , 
                                   
                                    ]>