django forms lazy来自数据库的数据

场景描述：

在通过forms渲染页面form时，如果通过form.Select渲染一个单选项，而恰好此时的可选项来自数据库时，若数据库中有数据是可以正常运行项目的，但当初始化项目，初始化数据库，没有数据时就会报错。

解决方案：

• 使用lazy函数。(from django.utils.functional import lazy)
• 使用注意：

lazy(models.Breed.objects.all().values_list,list)()

• 具体代码：

from django.utils.functional import lazy
class PetInformation(forms.ModelForm):
    name = CustomCharField(label="Name", help_text="Used to login, please remember your modification", )
    gender = CustomCharField(label="Gender", widget=forms.Select(choices=(("W", "Women"), ("M", "Man"), ("U","Unknown"))))
    weight = CustomCharField(label="Weight",)
    birth_date = CustomCharField(label="Birth Date", widget=forms.DateInput())
    color = CustomCharField(label="Color")
    photo = CustomCharField(label="Photo",widget=forms.FileInput())
    species = CustomCharField(label="Species", widget=forms.Select(choices=lazy(models.Species.objects.all().values_list,list)()))
    breed = CustomCharField(label="Breed", widget=forms.Select(choices=lazy(models.Breed.objects.all().values_list,list)()))

    class Meta:
        model = models.Pet
        exclude = ("join_date",)

• 如果涉及到instace的验证，应该使用ModelChoiceField
• 具体代码：

species = forms.ModelChoiceField(queryset=models.Species.objects.all(),label="Species",widget=forms.Select(attrs={"class":"form-control form-control-sm bg-light"}))
    breed = forms.ModelChoiceField(queryset=models.Breed.objects.all(),label="Species",widget=forms.Select(attrs={"class":"form-control form-control-sm bg-light"}))