python-django学习足迹(三)

django的ORM的概念

python的类对数据库的表进行操作

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django默认使用sqlite的数据库,默认自带sqlite的数据驱动,引擎名称: django.db.backends.sqlite3
mysql, 引擎名称: django.db.backends.mysql
pymysql:纯python的mysql驱动程序
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ORM —– object relation mapping(对象关系映射表) 类和表做映射
python的类

class emp():
    id = 1003
    name = 'chs'
    salary = 8000

# 一个实例就是一个记录
demo = emp()
demo.id

使用sqlite数据驱动调用数据库

django 默认的数据驱动是sqlite,切换成mysql需要更改settings.py

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': os.path.join(BASE_DIR, 'db.sqlite3'),
    }
}

在models.py中创建数据库表

from django.db import models

# Create your models here.



# create table book(
#   name varchar(32),
#   price float(4,2),
# )
# 创建一个书籍的表  一个表对应一个类
# 创建一个表必须继承models.Model类
class Book(models.Model):
    name = models.CharField(max_length=32)     # 字符串数据类型
    price = models.FloatField()       # IntegerField 整型
    pub_date = models.DateField()

# Book表创建完毕

在Terminal命令行输入命令: python manage.py makemigrations 创建初始化.py文件

此时在migrations目录下生成0001_initial.py

0001_initial.py

# Generated by Django 2.1 on 2018-08-24 07:20

from django.db import migrations, models


class Migration(migrations.Migration):

    initial = True

    dependencies = [
    ]

    operations = [
        migrations.CreateModel(
            name='Book',
            fields=[
                ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
                ('name', models.CharField(max_length=32)),
                ('price', models.FloatField()),
                ('pub_date', models.DateField()),
            ],
        ),
    ]

输入命令创建数据库表: python manage.py migrate

downloads->apply->ok

将db.sqlite3拖到Database窗口下

找到自定义创建的表book双击

可以直接添加数据到数据库表中

使用mysql数据驱动调用数据库

1.修改settings.py

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.mysql',
        'NAME': 'Django_ORM',    # 你的数据库名字
        'USER': 'root',     # 你的数据库用户名
        'PASSWORD': '123456',  # 你的数据库密码
        'HOST': '',         # 你的数据库主机,留空默认为localhost
                     # 此处写IP地址Django就能访问这台计算机下的数据库
        'PORT': '3306',     # 你的数据库端口


    }
}

2.执行Terminal命令: python manage.py makemigration
报错:Error loading MySQLdb module.
此时需要 在项目下找到初始化文件init.py
添加:

import pymysql

pymysql.install_as_MySQLdb()

这两句话告诉django默认驱动引擎不要用MySQLdb, 更换成pymysql

输入命令创建数据库表: python manage.py makemigrations
如果报错: No module named ‘pymysql’
可能是pymysql没有安装成功
此时在Terminal命令行输入命令: pip install pymysql安装即可

创建数据库表到django中:
输入命令: python manage.py migrate

在django上直接操作数据库表

修改表内容后可以在mySQL中找到修改的数据

mysql> use Django_ORM
Database changed
mysql> show tables;
+----------------------------+
| Tables_in_django_orm       |
+----------------------------+
| app01_book                 |
| auth_group                 |
| auth_group_permissions     |
| auth_permission            |
| auth_user                  |
| auth_user_groups           |
| auth_user_user_permissions |
| django_admin_log           |
| django_content_type        |
| django_migrations          |
| django_session             |
+----------------------------+
11 rows in set (0.00 sec)

mysql> desc app01_book;
+----------+-------------+------+-----+---------+----------------+
| Field    | Type        | Null | Key | Default | Extra          |
+----------+-------------+------+-----+---------+----------------+
| id       | int(11)     | NO   | PRI | NULL    | auto_increment |
| name     | varchar(32) | NO   |     | NULL    |                |
| price    | double      | NO   |     | NULL    |                |
| pub_date | date        | NO   |     | NULL    |                |
+----------+-------------+------+-----+---------+----------------+
4 rows in set (0.01 sec)

mysql>
mysql>
mysql> desc app01_book;
+----------+-------------+------+-----+---------+----------------+
| Field    | Type        | Null | Key | Default | Extra          |
+----------+-------------+------+-----+---------+----------------+
| id       | int(11)     | NO   | PRI | NULL    | auto_increment |
| name     | varchar(32) | NO   |     | NULL    |                |
| price    | double      | NO   |     | NULL    |                |
| pub_date | date        | NO   |     | NULL    |                |
+----------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

mysql>
mysql>
------------------------------------->在django中添加了author表
mysql> show tables;
+----------------------------+
| Tables_in_django_orm       |
+----------------------------+
| app01_author               |
| app01_book                 |
| auth_group                 |
| auth_group_permissions     |
| auth_permission            |
| auth_user                  |
| auth_user_groups           |
| auth_user_user_permissions |
| django_admin_log           |
| django_content_type        |
| django_migrations          |
| django_session             |
+----------------------------+
12 rows in set (0.00 sec)

mysql>

Django 在更新完数据库表后直接点击DB进行提交即可更新数据到数据库中

---

ORM对单表的增删改查

对单表添加字段
model.py

添加作者author字段,null=False 不允许默认值为null
添加完毕执行命令更新数据库表结构: python manage.py migrate
此时报错，基本内容为让root添加一个author的默认值

class Book(models.Model):
    name = models.CharField(max_length=32)     # 字符串数据类型
    price = models.FloatField()       # IntegerField 整型
    pub_date = models.DateField()
    author = models.CharField(max_length=32, null=False)
# Book表创建完毕

1.添加一个index.html页面
index.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

    <style>


        .head{
            line-height: 40px;
            background-color:orange;
            color:white;
            height:50px;
        }
    </style>


</head>
<body>

<div class="outer">

    <div class="head">标题</div>
    <div class="content">
        <a href="/addbook/">添加书籍</a>
        <a href="/update/">修改书籍</a>
        <a href="/delete/">删除书籍</a>
        <a href=""></a>



    </div>

</div>



</body>
</html>

2.添加路径

urls.py

from django.contrib import admin
from django.conf.urls import url

from app01 import views

urlpatterns = [
    url(r'^admin/', admin.site.urls),
    url(r'^index', views.index),
    url(r'^addbook', views.addbook),
    url(r'^update', views.update),
    url(r'^delete', views.delete),
]

3.试图函数实现功能
views.py

from django.shortcuts import render, HttpResponse

# Create your views here.
from app01.models import *

def index(req):
    return render(req, 'index.html')

# 增
def addbook(req):

    ## 方式一
    #add1 = Book(name="python2222", price=99, author='chung',
    #                    pub_date='2018-08-15')
    # 调用save方法将数据保存到数据库
    #add1.save()
    #return HttpResponse('添加成功!')


    ## 方式二
    Book.objects.create(name="天才在左疯子在右", price=69, author='chs',
                        pub_date='2018-08-15')
    return HttpResponse('添加成功!')


    #Book.objects.create(**dic)
    #return HttpResponse('添加成功!')


# 改
def update(req):

    ## 方式一
    Book.objects.filter(author='chs').update(price=100)
    return HttpResponse('修改成功!')

    ## 方式二
    '''
        第二种方式修改不能用get的原因是: update是QuerySet对象的方法
        get返回的是一个model对象,它没有update方法，而filter返回的是
        一个QuerySet对象(filter里面的条件可能有多个条件符合，比如
        author='chs',可能有两个author='chs'的行数据)
    '''
    #upd1 = Book.objects.get(author='chs')
    #upd1.price = 56
    #upd1.save()
    #return HttpResponse('修改成功!')

# 删
def delete(req):
    #找到表  调用objects
    Book.objects.filter(author='chung').delete()
    return HttpResponse('删除成功!')

ORM对单表的查询

1.添加路径

urlpatterns = [
    url(r'^select', views.select),
]

2.index.html 页面渲染

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>

    <style>


        .head{
            line-height: 40px;
            background-color:orange;
            color:white;
            height:50px;
        }
        span{
            color:red;
        }
    </style>


</head>
<body>

<div class="outer">

    <div class="head">标题</div>
    <div class="content">
        <a href="/addbook/">添加书籍</a>
        <a href="/update/">修改书籍</a>
        <a href="/delete/">删除书籍</a>
        <a href="/select/">查看书籍</a>
    </div>

    <hr>
    <div class="queryResult">

        {% for book in book_list %}
            <div>
                <p>书名: <span>{{ book.name }}</span></p>
                <p>作者: {{ book.author }}</p>
                <p>价格: {{ book.price }}</p>
                <p>创作时间: {{ book.pub_date }}</p>
                <hr>
            </div>
        {% endfor %}


    </div>

</div>

</body>
</html>

3.视图函数实现功能

from django.shortcuts import render, HttpResponse

# Create your views here.
from app01.models import *


# 查
def select(req):

    # 得到一个对象的集合
    book_list = Book.objects.all()

    # book_list = Book.objects.filter(id=2)
    # book_list = Book.objects.all()[::2]
    # book_list = Book.objects.all()[::-1]

    # first,last,get 取到的是一个实例对象，并非一个QuerySet的集合对象
    # book_list = Book.objects.first()
    # book_list = Book.objects.last()
    # get不会得到集合,只能取出一条记录的时候才不会报错
    # book_list = Book.objects.get(id=2)

    #ret = Book.objects.filter(author='chung').values('name', 'price')
    #print(ret)
    # 打印 <QuerySet [{'name': '河对岸', 'price': 57.0}]>

    # 查询除了author='chung'的书的信息
    # ret = Book.objects.exclude(author='chung').values('name', 'price')
    # print(ret)
    # 打印 <QuerySet [{'name': '清明水上', 'price': 100.0}, {'name': '天才在左
    # 疯子在右', 'price': 69.0}, {'name': 'PHP', 'price': 60.0}]>


    # 去重(某个字段重复)
    # book_list = Book.objects.all().values('name').distinct()
    # book_count = Book.objects.all().values('name').distinct().count()
    # print(book_count)
    # 打印 4


    return render(req, 'index.html', locals())

4.页面查询书籍效果

---

ORM对单表的模糊匹配查询

views.py

def select(req):

    # 万能的双下划线  __gt：大于  __lt：小于
    # book_list = Book.objects.filter(price__gt=50).values('name', 'price', 'author', 'pub_date')

    # 模糊查询 icontains:大小写不敏感  contains:敏感大小写
    book_list = Book.objects.filter(name__icontains='P').values('name', 'price', 'author', 'pub_date')

    return render(req, 'index.html', locals())

页面效果