Django系列4：数据常规操作级联数据PPTMysql使用定义模型关联（学生-班级）

109 阅读 0 评论 72 点赞

我是靠谱客的博主怕孤单手机，这篇文章主要介绍Django系列4：数据常规操作级联数据PPTMysql使用定义模型关联（学生-班级），现在分享给大家，希望可以做个参考。

PPT

Mysql使用

复制代码

1
2
mysql> create database HelloDjango charset=utf8;
Query OK, 1 row affected (0.01 sec)

安装pymysql

复制代码

1
2
3
4
5
6
7
8
9
10
pip install pymysql -i https://pypi.douban.com/simple
(venv) MacBookPro:HelloDjango zhangxm$ pip install pymysql
Collecting pymysql
Downloading https://files.pythonhosted.org/packages/ed/39/15045ae46f2a123019aa968dfcba0396c161c20f855f11dea6796bcaae95/PyMySQL-0.9.3-py2.py3-none-any.whl (47kB)
|████████████████████████████████| 51kB 196kB/s
Installing collected packages: pymysql
Successfully installed pymysql-0.9.3
WARNING: You are using pip version 19.3.1; however, version 20.0.2 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.

安装上以后系统仍然是不认这个库的，pymysql伪装成mysqlclient
比较常用的伪装写在程序的__init__.py中

复制代码

1
2
3
import pymysql
pymysql.install_as_MySQLdb()

Django - installing mysqlclient error: mysqlclient 1.3.13 or newer is required; you have 0.9.3

复制代码

1
2
3
4
5
6
7
8
9
10
11
12
##解决方法 仍然使用pymysql
1 )配置文件的目录中_init_.py中有如下代码
import pymysql
pymysql.install_as_MySQLdb()
# 这是一个hack，为了在Djano中替代默认的mysqlclient。mysqlclient官方描述：This is a fork of MySQLdb1
2) 点进去install_as_MySQLdb
找到version_info变量，改成
version_info = (1, 3, 13, "final", 0)
3) 改变django.db.backends.mysql.operations.py的一行代码
query = query.decode(errors='replace') -> query = query.encode(errors='replace')
原因：mysqlclient returns bytes object, PyMySQL returns str object
参考：https://github.com/PyMySQL/PyMySQL/issues/790#issuecomment-484201388

python manage.py startapp Three

想要承认项目的存在，更改project settings文件：

复制代码

1
2
3
4
5
6
7
8
9
10
11
12
13
INSTALLED_APPS = [
'django.contrib.admin',
'django.contrib.auth',
'django.contrib.contenttypes',
'django.contrib.sessions',
'django.contrib.messages',
'django.contrib.staticfiles',
'App',
'Two',
'Three'
# 'Three.apps.ThreeConfig' #1.9之后可以这样写
]

然后写Three里的路由规则

新建urls.py

复制代码

1
2
3
4
5
6
from django.conf.urls import url
from Three import views
urlpatterns = [
url('^index/', views.index),
]

views.py

复制代码

1
2
3
4
5
6
7
8
9
10
11
12
13
from django.http import HttpResponse
from django.shortcuts import render
# Create your views here.
from django.template import loader
def index(request):
three_index = loader.get_template("three_index.html")
context ={"student_name": '张三'
}
#有渲染，解析渲染引擎表达式的作用,如果不需要这些，直接open也可以
result = three_index.render(context=context)
print(result)
return HttpResponse(result)

Three->>templates->>index.html

复制代码

1
2
3
4
5
6
7
8
9
10
11
12
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Three_Index</title>
</head>
<body>
<h2>Three Index</h2>
{{ student_name }}
</body>
</html>

定义模型

python shell

关联（学生-班级）

model.py

复制代码

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
from django.db import models
# Create your models here.
class Grade(models.Model):
g_name = models.CharField(max_length=32)
class Student(models.Model):
s_name = models.CharField(max_length=16)
# django 升级到2.0之后,表与表之间关联的时候,必须要写on_delete参数,否则会报异常:
# TypeError: init() missing 1 required positional argument: ‘on_delete’
s_grade = models.ForeignKey(Grade,on_delete=models.CASCADE)
'''
on_delete=None,
# 删除关联表中的数据时,当前表与其关联的field的行为
on_delete=models.CASCADE,
# 删除关联数据,与之关联也删除
on_delete=models.DO_NOTHING,
# 删除关联数据,什么也不做
on_delete=models.PROTECT,
# 删除关联数据,引发错误ProtectedError
# models.ForeignKey('关联表', on_delete=models.SET_NULL, blank=True, null=True)
on_delete=models.SET_NULL,
# 删除关联数据,与之关联的值设置为null（前提FK字段需要设置为可空,一对一同理）
# models.ForeignKey('关联表', on_delete=models.SET_DEFAULT, default='默认值')
on_delete=models.SET_DEFAULT, # 删除关联数据,与之关联的值设置为默认值（前提FK字段需要设置默认值,一对一同理）
on_delete=models.SET,
# 删除关联数据,
a. 与之关联的值设置为指定值,设置：models.SET(值)
b. 与之关联的值设置为可执行对象的返回值,设置：models.SET(可执行对象)
'''

DDL python magange.py makemigrations, migrate

复制代码

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
-- auto-generated definition
create table Three_grade
(
id
int auto_increment
primary key,
g_name varchar(32) not null
);
create table Three_student
(
id
int auto_increment
primary key,
s_name
varchar(16) not null,
s_grade_id int
not null,
constraint Three_student_s_grade_id_ffbb8485_fk_Three_grade_id
foreign key (s_grade_id) references hellodjango.Three_grade (id)
);

Three->>templates-->student_three_list.html

复制代码

1
2
3
4
5
6
7
8
9
10
11
12
13
14
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Students List</title>
</head>
<body>
<ul>
{% for student in students %}
<li>{{ student.s_name }}</li>
{% endfor %}
</ul>
</body>
</html>

views.html

复制代码

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
from django.http import HttpResponse
from django.shortcuts import render
# Create your views here.
from django.template import loader
from Three.models import Student, Grade
def index(request):
three_index = loader.get_template("three_index.html")
context ={"student_name": '张三'
}
#有渲染，解析渲染引擎表达式的作用,如果不需要这些，直接open也可以
result = three_index.render(context=context)
print(result)
return HttpResponse(result)
#多获取1
def get_grade(request):
student = Student.objects.get(pk=1)
grade= student.s_grade
return HttpResponse("Grade %s",grade.g_name)
#一获取多
def get_students(request):
grade = Grade.objects.get(pk=1)
students = grade.student_set.all()
context = {
"students":students
}
return render(request, "students_three_list.html", context=context)