django之ORM介绍

LeonZhang0

2019-10-30

ORM

在进入ORM之前，先看一下传统的操作数据库的方式：

import pymysql
db = pymysql.connect(db= "guest",
        user="root",
        passwd="",
        host="127.0.0.1",)
cursor = db.cursor()
cursor.execute("select realname from sign_guest order by create_time")
name = [row[0] for row in cursor.fetchall()]
print(name)
[‘张三‘, ‘李四‘, ‘康‘, ‘李五‘, ‘lily‘, ‘zhangailing‘, ‘dulala‘, ‘adu‘, ‘tester01‘, ‘tester01‘, ‘tester02‘, ‘andy‘, ‘vivian‘]
2~5 ---- 首先要连接db
6   ---- 然后获得db的执行器对象
7   ---- 然后通过执行器运行sql，此时cursor对象相当于一个容器，存放了执行sql的结果
8   ---- 最后从cursor中取出来数据

是不是很费事？那么ORM到底是什么呢？ ORM就是可以把对db的增删改查等一系列操作通过class.method或者class.attribute的方式来操作，是不是很简单，那么看一下下面这个demo，这个demo就是设计并创建了表，可以先看一下代码demo：

from django.db import models
 
# Create your models here.
class UserMessage(models.Model):  # UserMessage对应db的表名
   name = models.CharField(max_length=20, verbose_name="用户名")
   email = models.EmailField(verbose_name="邮箱")
   address = models.CharField(max_length=100, verbose_name="联系地址")
   message = models.CharField(max_length=500, verbose_name="留言信息")
 
   class Meta:
      verbose_name = "用户留言信息"

开始演示---------

先贴出来demo的目录结构

首先在message这个应用下的models.py编写一个model代码

from django.db import models
 
# Create your models here.
class UserMessage(models.Model):  # UserMessage对应db的表名
   name = models.CharField(max_length=20, verbose_name="用户名")
   email = models.EmailField(verbose_name="邮箱")
   address = models.CharField(max_length=100, verbose_name="联系地址")
   message = models.CharField(max_length=500, verbose_name="留言信息")
 
   class Meta:
      verbose_name = "用户留言信息"

这里在项目目录执行makemigrations命令，创建model

D:\myproject\djangopro1
(venv3) $ python manage.py makemigrations message
System check identified some issues:
 
WARNINGS:
?: (2_0.W001) Your URL pattern ‘^form/$‘ has a route that contains ‘(?P<‘, begins with a ‘^‘, or ends with a ‘$‘. This was likely an oversight when migrating to django.urls.path().
Migrations for ‘message‘:
  message\migrations\0001_initial.py
    - Create model UserMessage

注意：message在django工程里是一个应用的角色，要注册到djangopro1工程的djangopro1里的settings.py中（图中的2，暂时理解为工程主配置应用）

命令执行如果没有报错，继续执行migrate，如下：

D:\myproject\djangopro1
(venv3) $ python manage.py migrate message
System check identified some issues:
 
WARNINGS:
?: (2_0.W001) Your URL pattern ‘^form/$‘ has a route that contains ‘(?P<‘, begins with a ‘^‘, or ends with a ‘$‘. This was likely an oversight when migrating to django.urls.path().
Operations to perform:
  Apply all migrations: message
Running migrations:
  Applying message.0001_initial... OK

到这里UserMessage表就创建成功了，可以在db看一下表结构