7.6. Django model

7.6.1. Django ORM ¶

The Django model uses its own ORM.

Object-relational mapping (Object Relational Mapping, referred to as ORM) is used to realize the conversion between data of different types of systems in object-oriented programming languages.

ORM acts as a bridge between the business logic layer and the database layer.

ORM automatically persists objects in the program to the database by using metadata that describes the mapping between the object and the database.

Benefits of using ORM:

• Improve the efficiency of development.

• Different databases can be switched smoothly.

Disadvantages of using ORM:

• When ORM code is converted into SQL statements, it takes a certain amount of time, and the execution efficiency will be reduced.

• Writing ORM code for a long time will reduce the ability to write SQL statements.

ORM parsing process:

• 1、ORM 会将 Python 代码转成为 SQL 语句。

• 2、SQL 语句通过 pymysql 传送到数据库服务端。

• 3、在数据库中执行 SQL 语句并将结果返回。

ORM correspondence table:

7.6.2. Database configuration ¶

7.6.3. How Django uses mysql Database ¶

Create a MySQL database (ORM cannot operate to the database level, only to data tables) syntax:

create database 数据库名称 default charset=utf8; # 防止编码问题，指定为 utf8

For example, we create a database called runoob, and the encoding is specified as utf8:

create database runoob default charset=utf8;

We found the DATABASES configuration item in the settings.py file of the project and modified its information as follows:

DATABASES= {'default': {'ENGINE':'django.db.backends.mysql',#
数据库引擎'NAME':'runoob',# 数据库名称'HOST':'127.0.0.1',#
数据库地址，本机 ip 地址 127.0.0.1'PORT':3306,# 端口'USER':'root',#
数据库用户名'PASSWORD':'123456',# 数据库密码} }

# 在与 settings.py 同级目录下的 \__init__.py 中引入模块和进行配置
import pymysql
pymysql.install_as_MySQLdb()

7.6.4. Define the model ¶

7.6.5. Create APP ¶

Django states that if you want to use a model, you must create an app. Let’s create an app for TestModel using the following command:

django-admin startapp TestModel

The directory structure is as follows:

HelloWorld
|-- HelloWorld
|-- manage.py
...
|-- TestModel
|   |-- __init__.py
|   |-- admin.py
|   |-- models.py
|   |-- tests.py
|   `-- views.py

Let’s modify the TestModel/models.py file with the following code:

#
models.pyfromdjango.dbimportmodelsclassTest(models.Model):name=models.CharField(max_length=20)

INSTALLED_APPS = (
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'TestModel',               # 添加此项
)

$ python3 manage.py migrate   # 创建表结构

$ python3 manage.py makemigrations TestModel  # 让 Django 知道我们在我们的模型有一些变更
$ python3 manage.py migrate TestModel   # 创建表结构

Creating tables ...
……
Creating table TestModel_test  #我们自定义的表
……

7.6.6. Common error message ¶

If you execute the above command, the following error message appears:

The reason is that MySQLclient only supports Python3.4, so if you use a later version of python, you need to modify it as follows:

通过报错信息的文件路径找到 …site-packagesDjango-2.0-py3.6.eggdjangodbbackendsmysql 这个路径里的 base.py 文件，把这两行代码注释掉（代码在文件开头部分）：

if version < (1, 3, 13):
    raise ImproperlyConfigured('mysqlclient 1.3.13 or newer is required; you have %s.' % Database.__version__)

In general, the code file path information of the error report will automatically jump to the number of lines in the error file, and at this time we comment out the number of code lines reported.

If the following error message appears:

We click on the path of the error code file and jump to the number of lines in the error file. In this case, we add the following before the number of code lines reported:

query = query.encode()

7.6.7. Database operation ¶

Next, let’s add the testdb.py file to the HelloWorld directory (described below) and modify the urls.py:

fromdjango.urlsimportpathfrom.importviews,testdburlpatterns=[path('runoob/',views.runoob),path('testdb/',testdb.testdb),]

7.6.8. Add data ¶

To add data, you need to create an object before executing the save function, which is equivalent to INSERT in SQL:

# -*- coding: utf-8
-*-fromdjango.httpimportHttpResponsefromTestModel.modelsimportTest#
数据库操作deftestdb(request):test1=Test(name='runoob')test1.save()returnHttpResponse("<p>数据添加成功！</p>")

7.6.9. Get data ¶

Django provides several ways to get the contents of the database, as shown in the following code:

# -*- coding: utf-8
-*-fromdjango.httpimportHttpResponsefromTestModel.modelsimportTest#
数据库操作deftestdb(request):# 初始化response=""response1=""#
通过objects这个模型管理器的all()获得所有数据行，相当于SQL中的SELECT \*
FROMlist=Test.objects.all()#
filter相当于SQL中的WHERE，可设置条件过滤结果response2=Test.objects.filter(id=1)#
获取单个对象response3=Test.objects.get(id=1)# 限制返回的数据 相当于 SQL
中的 OFFSET 0 LIMIT
2;Test.objects.order_by('name')[0:2]#数据排序Test.objects.order_by("id")#
上面的方法可以连锁使用Test.objects.filter(name="runoob").order_by("id")#
输出所有数据forvarinlist:response1+=var.name+""response=response1returnHttpResponse("<p>"+response+"</p>")

7.6.10. Update data ¶

You can use save () or update () to modify the data:

# -*- coding: utf-8
-*-fromdjango.httpimportHttpResponsefromTestModel.modelsimportTest#
数据库操作deftestdb(request):#
修改其中一个id=1的name字段，再save，相当于SQL中的UPDATEtest1=Test.objects.get(id=1)test1.name='Google'test1.save()#
另外一种方式#Test.objects.filter(id=1).update(name='Google')#
修改所有的列#
Test.objects.all().update(name='Google')returnHttpResponse("<p>修改成功</p>")

7.6.11. Delete data ¶

To delete an object in the database, simply call the object’s delete () method:

# -*- coding: utf-8
-*-fromdjango.httpimportHttpResponsefromTestModel.modelsimportTest#
数据库操作deftestdb(request):#
删除id=1的数据test1=Test.objects.get(id=1)test1.delete()# 另外一种方式#
Test.objects.filter(id=1).delete()# 删除所有数据#
Test.objects.all().delete()returnHttpResponse("<p>删除成功</p>")