orm的操作：

settings：

"""
Django settings for about_exam project.

Generated by 'django-admin startproject' using Django 1.11.26.

For more information on this file, see
https://docs.djangoproject.com/en/1.11/topics/settings/

For the full list of settings and their values, see
https://docs.djangoproject.com/en/1.11/ref/settings/
"""

import os

# Build paths inside the project like this: os.path.join(BASE_DIR, ...)
#定义项目根目录：
BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))


# Quick-start development settings - unsuitable for production
# See https://docs.djangoproject.com/en/1.11/howto/deployment/checklist/

# SECURITY WARNING: keep the secret key used in production secret!
SECRET_KEY = '07k_$&dsr2qjyw=*oz#bum20gtj^6k_c!#u2%7ixbad7q51zpr'

# SECURITY WARNING: don't run with debug turned on in production!
DEBUG = True

ALLOWED_HOSTS = []


# Application definition

#定义注册的app：
INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'app01.apps.App01Config',
]

MIDDLEWARE = [
    'django.middleware.security.SecurityMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.common.CommonMiddleware',
    'django.middleware.csrf.CsrfViewMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'django.contrib.messages.middleware.MessageMiddleware',
    'django.middleware.clickjacking.XFrameOptionsMiddleware',
]

ROOT_URLCONF = 'about_exam.urls'

#定义中间件：
TEMPLATES = [
    {
        'BACKEND': 'django.template.backends.django.DjangoTemplates',
        'DIRS': [os.path.join ( BASE_DIR, 'templates' )]
        ,
        'APP_DIRS': True,
        'OPTIONS': {
            'context_processors': [
                'django.template.context_processors.debug',
                'django.template.context_processors.request',
                'django.contrib.auth.context_processors.auth',
                'django.contrib.messages.context_processors.messages',
            ],
        },
    },
]

WSGI_APPLICATION = 'about_exam.wsgi.application'


# Database
# https://docs.djangoproject.com/en/1.11/ref/settings/#databases

#定义使用默认的数据库：
DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': os.path.join(BASE_DIR, 'db.sqlite3'),
    }
}


# Password validation
# https://docs.djangoproject.com/en/1.11/ref/settings/#auth-password-validators

AUTH_PASSWORD_VALIDATORS = [
    {
        'NAME': 'django.contrib.auth.password_validation.UserAttributeSimilarityValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.MinimumLengthValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.CommonPasswordValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.NumericPasswordValidator',
    },
]


# Internationalization
# https://docs.djangoproject.com/en/1.11/topics/i18n/

LANGUAGE_CODE = 'en-us'

TIME_ZONE = 'UTC'

USE_I18N = True

USE_L10N = True

USE_TZ = True


# Static files (CSS, JavaScript, Images)
# https://docs.djangoproject.com/en/1.11/howto/static-files/

#定义静态文件：
STATIC_URL = '/static/'
orm表数据：

请根据上述表结构的写出对应的model。注：性别中1代表男，2代表女；反向查询可使用related_name

 models：

from django.db import models

# Create your models here.

#定义班级表：
class Classes(models.Model):
    c_name = models.CharField(max_length=32)
    #定义班级和老师是多对多关系ManyToManyField：
    teachers = models.ManyToManyField("Teacher")

#定义老师表：
class Teacher(models.Model):
    t_name = models.CharField(max_length=32)
    #定义性别长度字段默认是1、有选择的1代表男和2代表女：
    sex = models.CharField(max_length=1,choices=(("1","男"),("2","女")))
    #定义年龄IntegerField整数：
    age = models.IntegerField()

#定义学生表：
class Student(models.Model):
    s_name = models.CharField(max_length=32)
    score = models.IntegerField()
    #定义学生表多对一班级表、on_delete=models.CASCADE级联删除：
    my_class = models.ForeignKey("Classes",on_delete=models.CASCADE)
数据库迁移命令：

python manage.py makemigrations

python manage.py migrate

 exam:

import os
#定义环境配置为django模板的settings文件：
os.environ.setdefault("DJANGO_SETTINGS_MODULE","about_exam.settings")
import django
django.setup()
from app01 import models

写出具体的ORM语句。
1.查寻Py27期的所有同学的名字--通过班级查找所有同学的名字
classs = models.Classes.objects.get(c_name="Py27期")
ret = classs.student_set.all().values("s_name") #方式一：
ret = models.Student.objects.filter(my_class__c_name="Py27期").values("s_name")  #方式二：
print(ret)
结果：<QuerySet [{'s_name': '小红'}, {'s_name': '小强'}]>

2.查询id不为5的所有学生对象
ret = models.Student.objects.exclude(pk=5)  #exclude是排除的意思：
print(ret)
结果：<QuerySet [<Student: Student object>, <Student: Student object>, <Student: Student object>, <Student: Student object>, <Student: Student object>]>

3.查询id大于等于2的老师对象
ret = models.Teacher.objects.filter(pk__gte=2)  #__gte是大于等于的意思：
print(ret)
结果：<QuerySet [<Teacher: Teacher object>, <Teacher: Teacher object>]>

4.查询分数小于等于60分的同学的成绩和姓名
ret = models.Student.objects.filter(score__lte=60).values("s_name","score")  #__lte是小于等于的意思
print(ret)
结果：<QuerySet [{'s_name': '小红', 'score': 45}, {'s_name': '小黑', 'score': 55}]>

5.新增一个名为“Py30期”的班级
models.Classes.objects.create(c_name="Py30期")   #方式一：
obj = models.Classes(c_name="Py30期")            #方式二：
obj.save()

6.给Py27期新增一个名为“小白”的同学
models.Student.objects.create(s_name="小白",score=0,my_class_id=1)    #方式一：
models.Student.objects.create(s_name="小白",score=0,my_class=models.Classes.objects.get(c_name="Py27期"))  #方式二：
class_obj = models.Classes.objects.get(c_name="Py27期")
class_obj.student_set.create(s_name="小白",score=0)   #方式三：

7.给Py27期，新增一个名为“Alex”的84岁男老师
class_obj = models.Classes.objects.get(c_name="Py27期")
class_obj.teachers.create(t_name="Alex",age=84,sex=1)

8.小白转班了，转到了Py28期
student_obj = models.Student.objects.get(s_name="小白")
student_obj.my_class = models.Classes.objects.get(c_name="Py28期")   #方式一：
student_obj.save()
models.Student.objects.filter(s_name="小白").update(my_class=models.Classes.objects.get(c_name="Py28期"))  #方式二：

9.查询出bigbao所教的所有学生的姓名和成绩
teacher_obj = models.Teacher.objects.get(t_name="bigbao")
classs = teacher_obj.classes_set.all()  #使用反向查询classes_set：
for i in classs:                                                  #方式一：
    print(i.student_set.values("s_name","score"))
ret = models.Student.objects.filter(my_class__teachers__t_name="bigbao").values("s_name","score")   #方式二：
print(ret)
结果：  <QuerySet [{'s_name': '小红', 'score': 45}, {'s_name': '小强', 'score': 100}]>
        <QuerySet [{'s_name': '大绿', 'score': 61}, {'s_name': '小黑', 'score': 55}, {'s_name': '小白', 'score': 0}]>

10.查询年纪最大的老师姓名和年龄
ret = models.Teacher.objects.all().order_by("-age").values("t_name","age").first()
print(ret)
结果：{'t_name': 'Alex', 'age': 84}

11.查询名字中有“小”的学生姓名和成绩，并按照成绩降序排列
ret = models.Student.objects.filter(s_name__contains="小").values("s_name","score").order_by("-score")   #包含用__contains
print(ret)
结果：<QuerySet [{'s_name': '小强', 'score': 100}, {'s_name': '小绿', 'score': 98}, {'s_name': '小黑', 'score': 55}, {'s_name': '小红', 'score': 45}, {'s_name': '小白', 'score': 0}]>

12.修改小红的成绩为60
models.Student.objects.filter(s_name="小红").update(score="60")

13.修改和尚老师和班级的对应关系，和尚老师带Py27期、Py28期、Py29期三个班级
t_obj = models.Teacher.objects.get(t_name="和尚")
t_obj.classes_set.set(models.Classes.objects.filter(c_name__in=["Py27期","Py28期","Py29期"]))

14.金老板不带班了，需要清除他和所带班级的关系。
t_obj = models.Teacher.objects.get(t_name="金老板")
t_obj.classes_set.clear()   #方式一：
t_obj.classes_set.set([])   #方式二：

# 15.查询Py27期的所有的老师
class_obj = models.Classes.objects.get(c_name="Py27期")
ret = class_obj.teachers.all()                                   #方式一：
ret = models.Teacher.objects.filter(classes__c_name="Py27期")    #方式二：
print(ret)
结果：<QuerySet [<Teacher: Teacher object>, <Teacher: Teacher object>, <Teacher: Teacher object>, <Teacher: Teacher object>]>