Python Django form組件動態從數據庫取choices數據的方式

from django.db import models
 
class UserInfo(models.Model):
  username = models.CharField(max_length=16)
  password = models.CharField(max_length=16)
  mobile = models.CharField(max_length=11)
 
class City(models.Model):
  name = models.CharField(max_length=16, null=False, unique=True)

from django.shortcuts import render, HttpResponse
from app01 import models
 
from django import forms
from django.forms import widgets
from django.core.validators import RegexValidator
from django.core.exceptions import ValidationError
 
 
class RegForm(forms.Form):
  username = forms.CharField(
    min_length=5,
    label="用戶名",
    error_messages={
      "min_length": "用戶名不能小于5位！",
      "required": "該字段不能為空"
    },
    widget=widgets.TextInput(attrs={"class": "form-control"})
  )
 
  password = forms.CharField(
    min_length=6,
    label="密碼",
    error_messages={
      "min_length": "密碼不能少于6位！",
      "required": "該字段不能為空"
    },
    widget=widgets.PasswordInput(attrs={"class": "form-control"}, render_value=True)
  )
 
  re_password = forms.CharField(
    min_length=6,
    label="確認密碼",
    error_messages={
      "required": "該字段不能為空"
    },
    widget=widgets.PasswordInput(attrs={"class": "form-control"}, render_value=True)
  )
 
  mobile = forms.CharField(
    label="手機號",
    # 自定義正則匹配規則
    validators=[
      RegexValidator(r'^[0-9]+$', "手機號必須是數字"), # 判斷手機號是否為數字
      RegexValidator(r'^1[3-9][0-9]{9}$', "手機格式有誤") # 判斷手機號是否為 1 和 3-9 開頭的十一位數
    ],
    error_messages={
      "required": "該字段不能為空",
    },
    widget=widgets.TextInput(attrs={"class": "form-control"})
  )
 
  city = forms.ChoiceField(
    choices=models.City.objects.values_list("id", "name"),
    label="城市",
    initial=2,
    widget=widgets.Select()
  )
 
  # 重寫父類的 __init__ 方法
  def __init__(self, *args, **kwargs):
    super().__init__(*args, **kwargs)
    self.fields['city'].widget.choices = models.City.objects.values_list("id", "name")
 
  # 判斷用戶名信息
  def clean_username(self):
    value = self.cleaned_data.get("username")
    if "admin" in value:
      raise ValidationError("用戶名不能含有敏感信息")
 
  # 重寫父類的 clean 方法
  def clean(self):
    password = self.cleaned_data.get("password")
    re_password = self.cleaned_data.get("re_password")
    if re_password != password:
      self.add_error("password", ValidationError("兩次密碼不一致"))
      self.add_error("re_password", ValidationError("兩次密碼不一致"))
      raise ValidationError("兩次密碼不一致")
    return self.cleaned_data
 
 
def reg2(request):
  form_obj = RegForm() # GET 請求
 
  if request.method == "POST":
    form_obj = RegForm(request.POST)
    # 讓 form 來幫我們進行校驗
    if form_obj.is_valid():
      # 如果通過校驗
      # 所有經過校驗的數據都保存在 form_obj.cleaned_data
      print(form_obj.cleaned_data)
      models.UserInfo.objects.create(**form_obj.cleaned_data)
      return HttpResponse("注冊成功")
 
  return render(request, "reg2.html", {"form_obj": form_obj})