Django-ORM的使用

一、表字段的增删改查  

• 新增

from django.db import models


# Create your models here.

class User(models.Model):
    id = models.AutoField(primary_key=True)
    name = models.CharField(max_length=32)
    pwd = models.CharField(max_length=32)
    addr= models.CharField(max_length=64)    # 新增addr字段

注意：对于已存在数据的表，新增字段必须要给定默认值，默认值有两种方法

如果models.py里没有指定默认值，执行python3  manage.py makemigrations时，会提示以下信息

'''
D:codemylogin>python3 manage.py makemigrations
You are trying to add a non-nullable field 'addr' to user without a default; we can't do that (the database needs something to populate existing rows).
Please select a fix:
 1) Provide a one-off default now (will be set on all existing rows with a null value for this column)
 2) Quit, and let me add a default in models.py

'''

选择1，就是在makemigrations时添加新字段的默认值

Select an option: 1
Please enter the default value now, as valid Python
The datetime and django.utils.timezone modules are available, so you can do e.g. timezone.now
Type 'exit' to exit this prompt
>>> 'shanghai'
Migrations for 'app01':
  app01migrations002_user_addr.py
    - Add field addr to user

D:codemylogin>python3 manage.py migrate
Operations to perform:
  Apply all migrations: admin, app01, auth, contenttypes, sessions
Running migrations:
  Applying app01.0002_user_addr... OK

在models.py里指定新字段的默认值

from django.db import models


# Create your models here.

class User(models.Model):
    id = models.AutoField(primary_key=True)
    name = models.CharField(max_length=32)
    pwd = models.CharField(max_length=32)
    addr= models.CharField(max_length=64)
    phone=models.CharField(max_length=11,default='')

• 修改字段

from django.db import models


# Create your models here.

class User(models.Model):
    id = models.AutoField(primary_key=True)
    name = models.CharField(max_length=32)
    pwd = models.CharField(max_length=32)
    addr= models.CharField(max_length=128)      # max_length=64改为28
    phone_num=models.CharField(max_length=11,default='')          # phone 改为phone_num

D:codemylogin>python3 manage.py makemigrations
Did you rename user.phone to user.phone_num (a CharField)? [y/N] y                 # 对于已上线的项目 谨慎做修改字段名的操作
Migrations for 'app01':
  app01migrations004_auto_20190312_1403.py
    - Rename field phone on user to phone_num
    - Alter field addr on user

D:codemylogin>python3 manage.py migrate
Operations to perform:
  Apply all migrations: admin, app01, auth, contenttypes, sessions
Running migrations:
  Applying app01.0004_auto_20190312_1403... OK

• 删除字段(同理，对于已上线的项目，删除字段慎之又慎，别给自己找麻烦)

from django.db import models


# Create your models here.

class User(models.Model):
    id = models.AutoField(primary_key=True)
    name = models.CharField(max_length=32)
    pwd = models.CharField(max_length=32)
    addr= models.CharField(max_length=128)
    # phone_num=models.CharField(max_length=11,default='')      # 注释就是删除

D:codemylogin>python3 manage.py makemigrations
Migrations for 'app01':
  app01migrations005_remove_user_phone_num.py
    - Remove field phone_num from user

D:codemylogin>python3 manage.py migrate
Operations to perform:
  Apply all migrations: admin, app01, auth, contenttypes, sessions
Running migrations:
  Applying app01.0005_remove_user_phone_num... OK

二、单表数据增删改查 

• 查询单条数据  user = models.User.objects.filter(name=name, pwd=pwd).first() 
• 返回的是user对象，可以通过user.name得到属性的值

def login(request):
    if request.method == 'GET':
        return render(request, 'login.html')
    else:
        # 取出POST中携带的参数
        name = request.POST.get('name')
        pwd = request.POST.get('pwd')
        if name and pwd:
            # 去数据库里查
            user = models.User.objects.filter(name=name, pwd=pwd).first()
            # print(user.name,user.pwd)  # user是一个实例对象  对象.属性 可获取到属性的值
            if user:  # user有值的情况
                return redirect('https://www.baidu.com')
            else:
                return HttpResponse('用户名或密码错误')
        else:
            return HttpResponse('用户名或密码不能为空')

• 查询所有数据  ret = models.User.objects.all()
• 返回的是QuerySet对象 [<User: User object (1)>, <User: User object (2)>]
• 通过render渲染，返回给前台展示   return render(request, 'userlist.html', {'userlist': ret})

def userlist(request):
    # 查出 User表中的所有数据
    # sql: select * from app01_user;
    ret = models.User.objects.all()  # orm返回一个QuerySet对象django.db.models.query.QuerySet
    return render(request, 'userlist.html', {'userlist': ret})

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>账号列表</title>
    <link rel="stylesheet" href="/static/bootstrap/css/bootstrap.min.css">
</head>
<h3>
    <a href="/useradd/">新增用户</a>
</h3>


<table class="table table-bordered table-responsive">
    <thread>
        <tr>
            <th>id</th>
            <th>name</th>
            <th>pwd</th>
            <th>addr</th>
            <th>操作</th>
        </tr>
    </thread>
    <tbody>
    {% for user in userlist %}
        <tr>
            <td>{{ user.id }}</td>
            <td>{{ user.name }}</td>
            <td>{{ user.pwd }}</td>
            <td>{{ user.addr }}</td>
            <td>
                <a href="/useredit?id={{ user.id }}">修改</a>
                <a href="/userdel?id={{ user.id }}">删除</a>
                <a href="/useredit?id={{ user.id }}">修改</a>
            </td>

        </tr>
    {% endfor %}

    </tbody>
</table>
<body>

</body>
</html>

• 删除记录  先通过filter方法查出数据，再调delete方法删除之   models.User.objects.filter(id=id).delete()
• 返回的是：影响的行数
• 前端可通过get携带参数    <a href="/userdel?id={{ user.id }}">删除</a>

def userdel(request):
    # 取出前端传过来的id
    id = request.GET.get('id')
    ret = models.User.objects.filter(id=id).delete()
    print(ret, type(ret))
    return redirect('/userlist/')

• 新增数据 
• 方式1：models.User.objects.create(name=name, pwd=pwd, addr=addr)     # 调用create()方法创建一条新纪录
• 方式2：models.User(name=name, pwd=pwd, addr=addr).save()   # 先生成一个新的user对象，再调save方法保存到数据库
• 前端的form表单中的数据在post到后端时，将form表单的数据以key=value&key=value的格式打包到body里：name=lck&pwd=1234  可通过request.body拿到

def useradd(request):
    if request.method == 'GET':
        return render(request, 'useradd.html')
    elif request.method == 'POST':
        name = request.POST.get('name')
        pwd = request.POST.get('pwd')
        addr = request.POST.get('addr')

        if name and pwd and addr:
            # 方式1: create()方法创建一条新纪录
            # models.User.objects.create(name=name, pwd=pwd, addr=addr)
            # 方式2: 先生成一个新的user对象，再调save方法保存到数据库
            models.User(name=name, pwd=pwd, addr=addr).save()
            return redirect('/userlist/')
        else:
            return HttpResponse('用户名、密码、地址不能为空')

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>新增用户</title>
    <link rel="stylesheet" href="/static/bootstrap/css/bootstrap.min.css">
</head>
<body>
<form method="post">
    <div class="form-group">
        <label for="name">用户名</label>
        <input type="text" class="form-control" name="name" placeholder="用户名">
    </div>
    <div>
        <label for="pwd">密码</label>
        <input type="password" class="form-control" name="pwd" placeholder="密码">
    </div>
    <div>
        <label for="addr">地址</label>
        <input type="text" class="form-control" name="addr" placeholder="地址">
    </div>
    <button type="submit" class="btn btn-default">提交</button>
</form>
</body>
</html>

• 修改数据   models.User.objects.filter(id=id).update(name=name,pwd=pwd,addr=addr)  # 先通过前端get携带的id，调用filter方法查出对应数据，再调update方法更新
• 返回的是：影响的行数
• 后端逻辑：前端GET携带id请求，后端返回此id对应的数据，前端修改后POST提交到后端，后端完成数据更新

def useredit(request):
    if request.method == 'GET':
        id=request.GET.get('id')
        user=models.User.objects.filter(id=id).first()
        return render(request,'useredit.html',{'user':user})
    else:
        id=request.GET.get('id')  # 前端form的action的url里带了id 所以可以从GET里取出
        id1=request.POST.get('id') # 前端form表单里id隐藏了，所以亦可以从POST里取出
        name=request.POST.get('name')
        pwd=request.POST.get('pwd')
        addr=request.POST.get('addr')
        # user=models.User.objects.filter(id=id)  # 查出id对应的数据，然后update新数据
        # user.update(name=name,pwd=pwd,addr=addr)
        # 上面两行可以合并成一行
        models.User.objects.filter(id=id).update(name=name,pwd=pwd,addr=addr)
        return redirect('/userlist/')

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>修改用户信息</title>
    <link rel="stylesheet" href="/static/bootstrap/css/bootstrap.min.css">
</head>
<body>
<h2>修改用户信息</h2>
<div class="col-md-6 col-md-offset-3">
    <form action="/useredit/?id={{ user.id }}" method="post">
        <input type="hidden" name="id" value="{{ user.id }}" class="form-control">
        <p>用户名: <input type="text" name="name" value="{{ user.name }}" class="form-control"></p>
        <p>密码: <input type="password" name="pwd" value="{{ user.pwd }}" class="form-control"></p>
        <p>地址: <input type="text" name="addr" value="{{ user.addr }}" class="form-control"></p>
        <input type="submit" value="提交">
    </form>
</div>
</body>
</html>