使用Django Form解决表单数据无法动态刷新的两种方法

一、无法动态更新数据的实例

1. 如下,数据库中创建了班级表和教师表,两张表的对应关系为“多对多”

from django.db import models
class Classes(models.Model):
  title = models.CharField(max_length=32)
class Teacher(models.Model):
  name = models.CharField(max_length=32)
  t2c = models.ManyToManyField(Classes)

2. views的功能有查看、添加、编辑班级或教师表

from django.shortcuts import render, redirect
from school import models
from django.forms import Form, fields, widgets
#班级表单验证规则
class ClsForm(Form):
  title = fields.RegexField('老男孩', error_messages={'invalid': '请以 老男孩 开头'})
#教师表单验证规则
class TchForm(Form):
  name = fields.CharField(max_length=16, min_length=2, widget=widgets.TextInput(attrs={'class': 'form-control'}))
  t2c = fields.MultipleChoiceField(
    choices=models.Classes.objects.values_list('id', 'title'),
    widget=widgets.SelectMultiple(attrs={'class': 'form-control'})
  )
#查看班级列表
def classes(request):
  cls_list = models.Classes.objects.all()
  return render(request, 'classes.html', {'cls_list': cls_list})
#查看教师列表
def teachers(request):
  tch_list = models.Teacher.objects.all()
  return render(request, 'teachers.html', {'tch_list': tch_list})
#添加班级
def add_cls(request):
  if request.method == 'GET':
    obj = ClsForm()
    return render(request, 'add_classes.html', {'obj': obj})
  else:
    obj = ClsForm(request.POST)
    if obj.is_valid():
      models.Classes.objects.create(**obj.cleaned_data)
      return redirect('/school/classes/')
    return render(request, 'add_classes.html', {'obj': obj})
#添加教师
def add_tch(request):
  if request.method == 'GET':
    obj = TchForm()
    return render(request, 'add_teacher.html', {'obj': obj})
  else:
    obj = TchForm(request.POST)
    if obj.is_valid():
      tc = obj.cleaned_data.pop('t2c')  # 获取教师任课班级id
      tch_obj = models.Teacher.objects.create(name=obj.cleaned_data['name']) # 添加新教师姓名
      tch_obj.t2c.add(*tc)  # 添加新教师任课班级
      return redirect('/school/teachers/')
    return render(request, 'add_teacher.html', {'obj': obj})
#编辑班级
def edit_cls(request, nid):
  if request.method == 'GET':
    cls = models.Classes.objects.filter(id=nid).first()
    obj = ClsForm(initial={'title': cls.title})
    return render(request, 'edit_classes.html', {'nid': nid, 'obj': obj})
  else:
    obj = ClsForm(request.POST)
    if obj.is_valid():
      models.Classes.objects.filter(id=nid).update(**obj.cleaned_data)
      return redirect('/school/classes/')
    return render(request, 'edit_classes.html', {'nid': nid, 'obj': obj})
#编辑教师
def edit_tch(request, nid):
  if request.method == 'GET':
    tch = models.Teacher.objects.filter(id=nid).first()
    v = tch.t2c.values_list('id')  # 获取该教师任课班级的id
    cls_ids = list(zip(*v))[0] if list(zip(*v)) else []   # 格式化为列表类型
    obj = TchForm(initial={'name': tch.name, 't2c': cls_ids})
    return render(request, 'edit_teacher.html', {'nid': nid, 'obj': obj})
  else:
    obj = TchForm(request.POST)
    if obj.is_valid():
      tc = obj.cleaned_data.pop('t2c')  # 获取修改后的任课班级id
      # models.Teacher.objects.filter(id=nid).update(name=obj.cleaned_data['name'])   # 更新教师姓名方法1
      tch_obj = models.Teacher.objects.filter(id=nid).first()
      tch_obj.name = obj.cleaned_data['name']   # 更新教师姓名方法2
      tch_obj.save()
      tch_obj.t2c.set(tc)
      return redirect('/school/teachers/')
    return render(request, 'edit_teacher.html', {'nid': nid, 'obj': obj})

3. html文件

classe:

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>班级列表</title>
  <link rel="stylesheet" href="/static/plugins/bootstrap-3.3.7-dist/css/bootstrap.css" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >
</head>
<body>
<div style="width: 700px; margin: 30px auto">
  <a class="btn btn-default" href="/school/add_cls/" rel="external nofollow" style="margin-bottom: 10px">添加班级</a>
    <table class="table table-hover" border="1" cellspacing="0">
      <thead>
      <tr>
        <th>ID</th>
        <th>班级</th>
        <th>操作</th>
      </tr>
      </thead>
      <tbody>
        {% for item in cls_list %}
          <tr>
            <td>{{ item.id }}</td>
            <td>{{ item.title }}</td>
            <td><a href="/school/edit_cls/{{ item.id }}" rel="external nofollow" >编辑</a></td>
          </tr>
        {% endfor %}
      </tbody>
    </table>
</div>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>添加班级</title>
</head>
<body>
<h1>添加班级</h1>
<form action="/school/add_cls/" method="post">
  {% csrf_token %}
  <p>
    {{ obj.title }} {{ obj.errors.title.0 }}
  </p>
  <input type="submit" value="提交">
</form>
</body>
</html>
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>编辑班级</title>
</head>
<body>
<h1>编辑班级</h1>
<form action="/school/edit_cls/{{ nid }}" method="post">
  {% csrf_token %}
  <p>
    {{ obj.title }} {{ obj.errors.title.0 }}
  </p>
  <input type="submit" value="提交">
</form>
</body>
</html>

 teachers:

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>教师列表</title>
  <link rel="stylesheet" href="/static/plugins/bootstrap-3.3.7-dist/css/bootstrap.css" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >
</head>
<body>
<div style="width: 700px; margin: 30px auto">
  <a class="btn btn-default" href="/school/add_tch/" rel="external nofollow" style="margin-bottom: 10px">添加教师</a>
    <table class="table table-hover" border="1" cellspacing="0">
      <thead>
      <tr>
        <th>ID</th>
        <th>姓名</th>
        <th>任教班级</th>
        <th>操作</th>
      </tr>
      </thead>
      <tbody>
        {% for item in tch_list %}
          <tr>
            <td>{{ item.id }}</td>
            <td>{{ item.name }}</td>
            <td>
              {% for row in item.t2c.all %}
                <span style="border: solid gray 1px">{{ row.title }}</span>
              {% endfor %}
            </td>
            <td><a href="/school/edit_tch/{{ item.id }}" rel="external nofollow" >编辑</a></td>
          </tr>
        {% endfor %}
      </tbody>
    </table>
</div>
</body>
</html>
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>添加教师</title>
  <link rel="stylesheet" href="/static/plugins/bootstrap-3.3.7-dist/css/bootstrap.css" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >
</head>
<body>
<div style="width: 500px; margin: 20px auto">
<h3 style="width: 100px; margin: 10px auto">添加教师</h3>
  <form class="form-horizontal" action="/school/add_tch/" method="post">
    {% csrf_token %}
 <div class="form-group">
  <label class="col-sm-2 control-label">姓名</label>
  <div class="col-sm-10">
   {{ obj.name }} {{ obj.errors.name.0 }}
  </div>
 </div>
 <div class="form-group">
  <label class="col-sm-2 control-label">班级</label>
  <div class="col-sm-10">
      {{ obj.t2c }} {{ obj.errors.t2c.0 }}
  </div>
 </div>
 <div class="form-group">
  <div class="col-sm-offset-2 col-sm-10">
   <input type="submit" class="btn btn-default" value="提交"></input>
  </div>
 </div>
</form>
</div>
</body>
</html>
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>编辑教师</title>
  <link rel="stylesheet" href="/static/plugins/bootstrap-3.3.7-dist/css/bootstrap.css" rel="external nofollow" rel="external nofollow" rel="external nofollow" rel="external nofollow" >
</head>
<body>
<div style="width: 500px; margin: 20px auto">
<h3 style="width: 100px; margin: 10px auto">编辑教师</h3>
  <form class="form-horizontal" action="/school/edit_tch/{{ nid }}" method="post">
    {% csrf_token %}
 <div class="form-group">
  <label class="col-sm-2 control-label">姓名</label>
  <div class="col-sm-10">
   {{ obj.name }} {{ obj.errors.name.0 }}
  </div>
 </div>
 <div class="form-group">
  <label class="col-sm-2 control-label">班级</label>
  <div class="col-sm-10">
      {{ obj.t2c }} {{ obj.errors.t2c.0 }}
  </div>
 </div>
 <div class="form-group">
  <div class="col-sm-offset-2 col-sm-10">
   <input type="submit" class="btn btn-default" value="提交"></input>
  </div>
 </div>
</form>
</div>
</body>
</html>

4. 数据不能同步

在班级表中新增一条记录

在教师表中新添加一名教师,发现无法获取上一步新增记录

5. 原因分析

在添加教师时,请求方式为GET,html标签由Form组件自动生成,其中的数据也是由Form组件提供

而TchForm作为一个类,在project运行起来后,其中的name和t2c字段都是类的变量,其只执行一次,就将数据保存在内存中,无论之后生成多少个TchForm对象,其中的字段的值都不变。

所以会出现教师表中的班级多选列表无法动态更新。

二、解决上述bug的方法

每次更新数据库后重启project,让Form类重新初始化,能够让数据更新,但这显然是不切实际的。

知道了bug的根源,我们可以尝试让每次生成TchForm对象时就更新数据:

方法一

1. 利用 __init__将数据库操作放入对象变量中

 修改TchForm类

#教师表单验证规则
class TchForm(Form):
  name = fields.CharField(max_length=16, min_length=2, widget=widgets.TextInput(attrs={'class': 'form-control'}))
  t2c = fields.MultipleChoiceField(
    # choices=models.Classes.objects.values_list('id', 'title'),
    widget=widgets.SelectMultiple(attrs={'class': 'form-control'})
  )
  def __init__(self, *args, **kwargs):  # 自定义__init__
    super(TchForm, self).__init__(*args, **kwargs) # 调用父类的__init__
    self.fields['t2c'].choices = models.Classes.objects.values_list('id', 'title')  # 为字段t2c的choices赋值

2. 验证

 在班级表中新增一条记录

 再在教师表中添加

方法二

1. 利用django.forms.models模块中的queryset连接数据库

 修改TchForm类

#教师表单验证规则
from django.forms import models as form_models # 导入django.forms.models
class TchForm(Form):
  name = fields.CharField(max_length=16, min_length=2, widget=widgets.TextInput(attrs={'class': 'form-control'}))
  #重新定义字段
  t2c = form_models.ModelMultipleChoiceField(
    # choices=models.Classes.objects.values_list('id', 'title'),
    queryset=models.Classes.objects.all(), # 利用queryset连接数据库,只能连接object类型
    widget=widgets.SelectMultiple(attrs={'class': 'form-control'})
  )

2. 验证

由于TchForm类中,queryset只能连接object类型,所以,需要设置models.py中的Classes类的返回值。

 设置models.py中的Classes类的返回值

class Classes(models.Model):
  title = models.CharField(max_length=32)
   def __str__(self):
     return self.title

在班级表中新增一条记录

再在教师表中添加

以上所述是小编给大家介绍的使用Django Form解决表单数据无法动态刷新的两种方法,希望对大家有所帮助,如果大家有任何疑问请给我留言,小编会及时回复大家的。在此也非常感谢大家对菜鸟教程(cainiaojc.com)网站的支持!

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