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 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)
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.py INSTALLED_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 migrate
Operations to perform:
Apply all migrations: admin, auth, contenttypes, polls, sessions
Running 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() <QuerySet []> # 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=<UTC>) # 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() <QuerySet [<Question: Question object>]>
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 models import datetime from django.utils import timezone # Create your models here. from django.db import models class 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() <QuerySet [<Question: what's up>]>
，今天上课先写这些喽，继续学习新知识！！
于是我又回来了
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() <QuerySet [<Question: what's up>]> >>> Question.objects.filter(id=1) <QuerySet [<Question: what's up>]> >>> Question.objects.filter(question_text__startswith='What') <QuerySet []> >>> Question.objects.filter(question_text__startswith='What') <QuerySet []> >>> Question.objects.filter(question_text__startswith="What's") <QuerySet []> >>> Question.objects.filter(question_text__startswith='what') <QuerySet [<Question: what's up>]> >>> from django.utils import timezone File "<console>", 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: what's up> >>> Question.objects.get(id=2) Traceback (most recent call last): File "<console>", line 1, in <module> File "D:pysitemysitevenvlibsite-packagesdjangodbmodelsmanager.py", line 82, in manager_metho d return getattr(self.get_queryset(), name)(*args, **kwargs) File "D:pysitemysitevenvlibsite-packagesdjangodbmodelsquery.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) <Question: what's up> >>> q = Question.objects.get(pk=1) >>> q.was_published_recently() True >>> q.choice_set.all() <QuerySet []> >>> 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) >>> c.question <Question: what's up> >>> q.choice_set.all() <QuerySet [<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]> >>> q.choice_count() Traceback (most recent call last): File "<console>", line 1, in <module> AttributeError: 'Question' object has no attribute 'choice_count' >>> q.choice_set.count() 3 >>> Choice.objects.filter(question__pub_date__year=current_year) <QuerySet [<Choice: Not much>, <Choice: The sky>, <Choice: Just hacking again>]> >>> c = q.choice_set.filter(choice_text__startwith'Just hacking') File "<console>", 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 "<console>", line 1, in <module> File "D:pysitemysitevenvlibsite-packagesdjangodbmodelsmanager.py", line 82, in manager_metho d return getattr(self.get_queryset(), name)(*args, **kwargs) File "D:pysitemysitevenvlibsite-packagesdjangodbmodelsquery.py", line 892, in filter return self._filter_or_exclude(False, *args, **kwargs) File "D:pysitemysitevenvlibsite-packagesdjangodbmodelsquery.py", line 910, in _filter_or_exc lude clone.query.add_q(Q(*args, **kwargs)) File "D:pysitemysitevenvlibsite-packagesdjangodbmodelssqlquery.py", line 1290, in add_q clause, _ = self._add_q(q_object, self.used_aliases) File "D:pysitemysitevenvlibsite-packagesdjangodbmodelssqlquery.py", line 1318, in _add_q split_subq=split_subq, simple_col=simple_col, File "D:pysitemysitevenvlibsite-packagesdjangodbmodelssqlquery.py", line 1251, in build_fil ter condition = self.build_lookup(lookups, col, value) File "D:pysitemysitevenvlibsite-packagesdjangodbmodelssqlquery.py", line 1110, in build_loo kup lhs = self.try_transform(lhs, lookup_name) File "D:pysitemysitevenvlibsite-packagesdjangodbmodelssqlquery.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 "<console>", line 1, in <module> AttributeError: 'QuerySet' object has no attribute 'objects' >>> c.all() <QuerySet []> >>> q.choice_set.all() <QuerySet [<Choice: Not much>, <Choice: The sky>]>