Python Django admin根据模型中的字段验证内联表单集

我目前正在学习python和django，我被卡住了。我有以下型号：

class State(models.Model):
    name = models.CharField(max_length=30)
    population = models.IntegerField()

class Candidate(models.Model):
    name = models.CharField(max_length=30)

# Represents the election result of a particular Candidate in a particular State
class Result(models.Model):
    candidate = models.ForeignKey(Candidate)
    state = models.ForeignKey(State)
    num_votes = models.IntegerField()

My admin.py包含以下内容：

class CandidateAdmin(admin.ModelAdmin):
    fields = ['name']

class ResultInlineFormset(forms.models.BaseInlineFormSet):
    def clean(self):
        # Check that total number of votes doesn't exceed population
        sum = 0
        for form in self.forms:
            sum += form.cleaned_data.get('num_votes')
            # This is the part where I'm stuck
            if (sum > value_of_population_field_from_State_form):
                raise forms.ValidationError("Total number of votes cannot exceed state population")

class ResultInline(admin.TabularInline):
    model = Result
    extra = 0
    formset = ResultInlineFormset

class StateAdmin(admin.ModelAdmin):
    fields = ['name', 'population']
    inlines = [ResultInline]

admin.site.register(Candidate, CandidateAdmin)
admin.site.register(State, StateAdmin)

正如你所看到的，我需要以某种方式检查总票数（所有候选人的票数之和）是否高于该州的人口。要做到这一点，我想我需要以状态形式访问人口字段的值，但我不知道如何做，或者是否可能？

可能的重复项