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”
1 from django.db import models 2 3 4 class Classes(models.Model): 5 title = models.CharField(max_length=32) 6 7 8 class Teacher(models.Model): 9 name = models.CharField(max_length=32) 10 t2c = models.ManyToManyField(Classes)
2. views的功能有查看、添加、编辑班级或教师表
1 from django.shortcuts import render, redirect 2 from school import models 3 from django.forms import Form, fields, widgets 4 5 6 #班级表单验证规则 7 class ClsForm(Form): 8 title = fields.RegexField('老男孩', error_messages={'invalid': '请以 老男孩 开头'}) 9 10 11 #教师表单验证规则 12 class TchForm(Form): 13 name = fields.CharField(max_length=16, min_length=2, widget=widgets.TextInput(attrs={'class': 'form-control'})) 14 t2c = fields.MultipleChoiceField( 15 choices=models.Classes.objects.values_list('id', 'title'), 16 widget=widgets.SelectMultiple(attrs={'class': 'form-control'}) 17 ) 18 19 20 #查看班级列表 21 def classes(request): 22 cls_list = models.Classes.objects.all() 23 return render(request, 'classes.html', {'cls_list': cls_list}) 24 25 26 #查看教师列表 27 def teachers(request): 28 tch_list = models.Teacher.objects.all() 29 return render(request, 'teachers.html', {'tch_list': tch_list}) 30 31 32 #添加班级 33 def add_cls(request): 34 if request.method == 'GET': 35 obj = ClsForm() 36 return render(request, 'add_classes.html', {'obj': obj}) 37 else: 38 obj = ClsForm(request.POST) 39 if obj.is_valid(): 40 models.Classes.objects.create(**obj.cleaned_data) 41 return redirect('/school/classes/') 42 return render(request, 'add_classes.html', {'obj': obj}) 43 44 45 #添加教师 46 def add_tch(request): 47 if request.method == 'GET': 48 obj = TchForm() 49 return render(request, 'add_teacher.html', {'obj': obj}) 50 else: 51 obj = TchForm(request.POST) 52 if obj.is_valid(): 53 tc = obj.cleaned_data.pop('t2c') # 获取教师任课班级id 54 tch_obj = models.Teacher.objects.create(name=obj.cleaned_data['name']) # 添加新教师姓名 55 tch_obj.t2c.add(*tc) # 添加新教师任课班级 56 return redirect('/school/teachers/') 57 return render(request, 'add_teacher.html', {'obj': obj}) 58 59 60 #编辑班级 61 def edit_cls(request, nid): 62 if request.method == 'GET': 63 cls = models.Classes.objects.filter(id=nid).first() 64 obj = ClsForm(initial={'title': cls.title}) 65 return render(request, 'edit_classes.html', {'nid': nid, 'obj': obj}) 66 else: 67 obj = ClsForm(request.POST) 68 if obj.is_valid(): 69 models.Classes.objects.filter(id=nid).update(**obj.cleaned_data) 70 return redirect('/school/classes/') 71 return render(request, 'edit_classes.html', {'nid': nid, 'obj': obj}) 72 73 74 #编辑教师 75 def edit_tch(request, nid): 76 if request.method == 'GET': 77 tch = models.Teacher.objects.filter(id=nid).first() 78 v = tch.t2c.values_list('id') # 获取该教师任课班级的id 79 cls_ids = list(zip(*v))[0] if list(zip(*v)) else [] # 格式化为列表类型 80 obj = TchForm(initial={'name': tch.name, 't2c': cls_ids}) 81 return render(request, 'edit_teacher.html', {'nid': nid, 'obj': obj}) 82 else: 83 obj = TchForm(request.POST) 84 if obj.is_valid(): 85 tc = obj.cleaned_data.pop('t2c') # 获取修改后的任课班级id 86 # models.Teacher.objects.filter(id=nid).update(name=obj.cleaned_data['name']) # 更新教师姓名方法1 87 tch_obj = models.Teacher.objects.filter(id=nid).first() 88 tch_obj.name = obj.cleaned_data['name'] # 更新教师姓名方法2 89 tch_obj.save() 90 tch_obj.t2c.set(tc) 91 return redirect('/school/teachers/') 92 return render(request, 'edit_teacher.html', {'nid': nid, 'obj': obj})
3. html文件
classe：
1 <!DOCTYPE html> 2 <html lang="en"> 3 <head> 4 <meta charset="UTF-8"> 5 <title>班级列表</title> 6 <link rel="stylesheet" href="/static/plugins/bootstrap-3.3.7-dist/css/bootstrap.css"> 7 </head> 8 <body> 9 <div style=" 700px; margin: 30px auto"> 10 <a class="btn btn-default" href="/school/add_cls/" style="margin-bottom: 10px">添加班级</a> 11 <table class="table table-hover" border="1" cellspacing="0"> 12 <thead> 13 <tr> 14 <th>ID</th> 15 <th>班级</th> 16 <th>操作</th> 17 </tr> 18 </thead> 19 <tbody> 20 {% for item in cls_list %} 21 <tr> 22 <td>{{ item.id }}</td> 23 <td>{{ item.title }}</td> 24 <td><a href="/school/edit_cls/{{ item.id }}">编辑</a></td> 25 </tr> 26 {% endfor %} 27 </tbody> 28 </table> 29 </div> 30 </body> 31 </html>
1 <!DOCTYPE html> 2 <html lang="en"> 3 <head> 4 <meta charset="UTF-8"> 5 <title>添加班级</title> 6 </head> 7 <body> 8 <h1>添加班级</h1> 9 <form action="/school/add_cls/" method="post"> 10 {% csrf_token %} 11 <p> 12 {{ obj.title }} {{ obj.errors.title.0 }} 13 </p> 14 <input type="submit" value="提交"> 15 </form> 16 </body> 17 </html>
1 <!DOCTYPE html> 2 <html lang="en"> 3 <head> 4 <meta charset="UTF-8"> 5 <title>编辑班级</title> 6 </head> 7 <body> 8 <h1>编辑班级</h1> 9 <form action="/school/edit_cls/{{ nid }}" method="post"> 10 {% csrf_token %} 11 <p> 12 {{ obj.title }} {{ obj.errors.title.0 }} 13 </p> 14 <input type="submit" value="提交"> 15 </form> 16 </body> 17 </html>
teachers：
1 <!DOCTYPE html> 2 <html lang="en"> 3 <head> 4 <meta charset="UTF-8"> 5 <title>教师列表</title> 6 <link rel="stylesheet" href="/static/plugins/bootstrap-3.3.7-dist/css/bootstrap.css"> 7 </head> 8 <body> 9 <div style=" 700px; margin: 30px auto"> 10 <a class="btn btn-default" href="/school/add_tch/" style="margin-bottom: 10px">添加教师</a> 11 <table class="table table-hover" border="1" cellspacing="0"> 12 <thead> 13 <tr> 14 <th>ID</th> 15 <th>姓名</th> 16 <th>任教班级</th> 17 <th>操作</th> 18 </tr> 19 </thead> 20 <tbody> 21 {% for item in tch_list %} 22 <tr> 23 <td>{{ item.id }}</td> 24 <td>{{ item.name }}</td> 25 <td> 26 {% for row in item.t2c.all %} 27 <span style="border: solid gray 1px">{{ row.title }}</span> 28 {% endfor %} 29 </td> 30 <td><a href="/school/edit_tch/{{ item.id }}">编辑</a></td> 31 </tr> 32 {% endfor %} 33 </tbody> 34 </table> 35 </div> 36 </body> 37 </html>
1 <!DOCTYPE html> 2 <html lang="en"> 3 <head> 4 <meta charset="UTF-8"> 5 <title>添加教师</title> 6 <link rel="stylesheet" href="/static/plugins/bootstrap-3.3.7-dist/css/bootstrap.css"> 7 </head> 8 <body> 9 <div style=" 500px; margin: 20px auto"> 10 <h3 style=" 100px; margin: 10px auto">添加教师</h3> 11 <form class="form-horizontal" action="/school/add_tch/" method="post"> 12 {% csrf_token %} 13 <div class="form-group"> 14 <label class="col-sm-2 control-label">姓名</label> 15 <div class="col-sm-10"> 16 {{ obj.name }} {{ obj.errors.name.0 }} 17 </div> 18 </div> 19 <div class="form-group"> 20 <label class="col-sm-2 control-label">班级</label> 21 <div class="col-sm-10"> 22 {{ obj.t2c }} {{ obj.errors.t2c.0 }} 23 </div> 24 </div> 25 <div class="form-group"> 26 <div class="col-sm-offset-2 col-sm-10"> 27 <input type="submit" class="btn btn-default" value="提交"></input> 28 </div> 29 </div> 30 </form> 31 </div> 32 </body> 33 </html>
1 <!DOCTYPE html> 2 <html lang="en"> 3 <head> 4 <meta charset="UTF-8"> 5 <title>编辑教师</title> 6 <link rel="stylesheet" href="/static/plugins/bootstrap-3.3.7-dist/css/bootstrap.css"> 7 </head> 8 <body> 9 <div style=" 500px; margin: 20px auto"> 10 <h3 style=" 100px; margin: 10px auto">编辑教师</h3> 11 <form class="form-horizontal" action="/school/edit_tch/{{ nid }}" method="post"> 12 {% csrf_token %} 13 <div class="form-group"> 14 <label class="col-sm-2 control-label">姓名</label> 15 <div class="col-sm-10"> 16 {{ obj.name }} {{ obj.errors.name.0 }} 17 </div> 18 </div> 19 20 <div class="form-group"> 21 <label class="col-sm-2 control-label">班级</label> 22 <div class="col-sm-10"> 23 {{ obj.t2c }} {{ obj.errors.t2c.0 }} 24 </div> 25 </div> 26 <div class="form-group"> 27 <div class="col-sm-offset-2 col-sm-10"> 28 <input type="submit" class="btn btn-default" value="提交"></input> 29 </div> 30 </div> 31 </form> 32 </div> 33 </body> 34 </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
1 #教师表单验证规则 2 class TchForm(Form): 3 name = fields.CharField(max_length=16, min_length=2, widget=widgets.TextInput(attrs={'class': 'form-control'})) 4 t2c = fields.MultipleChoiceField( 5 # choices=models.Classes.objects.values_list('id', 'title'), 6 widget=widgets.SelectMultiple(attrs={'class': 'form-control'}) 7 ) 8 9 def __init__(self, *args, **kwargs): # 自定义__init__ 10 super(TchForm, self).__init__(*args, **kwargs) # 调用父类的__init__ 11 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
1 #教师表单验证规则 2 from django.forms import models as form_models # 导入django.forms.models 3 class TchForm(Form): 4 name = fields.CharField(max_length=16, min_length=2, widget=widgets.TextInput(attrs={'class': 'form-control'})) 5 #重新定义字段 6 t2c = form_models.ModelMultipleChoiceField( 7 # choices=models.Classes.objects.values_list('id', 'title'), 8 queryset=models.Classes.objects.all(), # 利用queryset连接数据库，只能连接object类型 9 widget=widgets.SelectMultiple(attrs={'class': 'form-control'}) 10 )
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。
1 class Classes(models.Model): 2 title = models.CharField(max_length=32) 3 4 def __str__(self): 5 return self.title
在班级表中新增一条记录
再在教师表中添加
