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 modelsclass Classes(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, redirectfrom school import modelsfrom django.forms import Form, fields, widgets#班级表单验证规则class ClsForm(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.modelsclass 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): 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VEVB武林网网站的支持！
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