重點是： Form類物件例項化的時候，在類裡邊__init()__函式中加入重新更新select資料來源

from django.shortcuts import render,redirect
from app3 import models
from app3 import form
from django import forms
from django.forms import widgets

#靜態欄位,value_list獲取列表[()]加元組返回值


class Fromdb(forms.Form):
    purpose = forms.CharField()
    user = forms.IntegerField(
        widget=widgets.Select()
        )
    #保證每次訪問重新獲取最新資料
    def __init__(self,*args,**kwargs):
        super(Fromdb,self).__init__(*args,**kwargs)
        self.fields["user"].widget.choices=models.Stu.objects.values_list("id", "name")

def formdb(request):
    stus = Fromdb()
    return render(request,"formdb.html",{"stus":stus})