如何在Django的BuildOrderForm下拉菜单中仅显示当前培训选项？

我开发了一个允许用户注册课程（基于TrainingInstance模型）的应用，这些课程在Training模型中被标记为「current（当前）」或「past（过去）」类别。当在模板中展示BuildOrderForm表单时，希望下拉菜单仅显示属于当前培训的选项。请问如何在不使用JavaScript或Ajax的情况下，在Django中实现该需求？

原代码 #

forms.py #

class BuildOrderForm(forms.ModelForm):
    class Meta:
        model = Order
        fields = ['training_registered']

models.py #

class Training(models.Model):
    """ Model which specifies the training category (name) and whether they are Past or Present""" 
    YEAR = (
        ('current', 'current'),
        ('past', 'past'),
        )
    name = models.CharField(max_length=200, null=True)
    year= models.CharField(max_length=200, null=True, choices=YEAR, default='current')
    def __str__(self):
        return self.name

class TrainingInstance(models.Model):
    """ Creates a model of different instances of each training ( May 2021 etc) """ 

    name = models.CharField(max_length=200, null=True, blank=True)
    venue = models.CharField(max_length=200, null=True, blank=True)
    training = models.ForeignKey(Training, on_delete= models.CASCADE, null = True)
    
    training_month = models.CharField(max_length=200, null=True, blank=True)
    participant_date = models.CharField(max_length=20, null=True, blank=True)
    staff_date = models.CharField(max_length=20, null=True, blank=True)
    graduation_date = models.CharField(max_length=200, null=True, blank=True)
    
    def __str__(self):
        return self.name
    
class Order(models.Model):
    REGSTATUS = (
        ('registered', 'registered'),
        ('enrolled', 'enrolled'),
        ('holding', 'holding'),
        ('withdrawn', 'withdrawn'),
        ('waiting', 'waiting'),
        )

    customer = models.ForeignKey(Customer, on_delete= models.CASCADE, null = True)
    training_registered = models.ForeignKey(TrainingInstance, on_delete= models.SET_NULL, blank = True, null = True)
    registration_date = models.DateTimeField(null=True,blank=True)

    regstatus = models.CharField(max_length=200, null=True, choices=REGSTATUS, default='registered')

    def __str__(self):
        return self.customer.username

解决方案 #

方法1：重写表单的__init__方法 #

在表单初始化时动态过滤training_registered字段的查询集，只保留关联「当前培训」的课程实例：

class BuildOrderForm(forms.ModelForm):
    class Meta:
        model = Order
        fields = ['training_registered']

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        # 利用ORM跨模型过滤，只保留关联year为current的TrainingInstance
        self.fields['training_registered'].queryset = TrainingInstance.objects.filter(
            training__year='current'
        )

方法2：显式定义字段并指定查询集 #

直接声明training_registered字段，同时设置过滤后的查询集，适合需要自定义字段属性（如标签、必填性）的场景：

class BuildOrderForm(forms.ModelForm):
    training_registered = forms.ModelChoiceField(
        queryset=TrainingInstance.objects.filter(training__year='current'),
        required=True,  # 根据业务需求调整是否必填
        label='注册课程'
    )

    class Meta:
        model = Order
        fields = ['training_registered']

关键说明 #

• 两种方案均通过Django ORM的跨模型关联查询（双下划线training__year表示关联到Training模型的year字段）在后端完成数据筛选，完全不需要前端JS/Ajax参与。
• 如果需要保留空选项（允许用户不选择课程），可将required设为False，Django默认会添加空选项；也可通过empty_label参数自定义空选项文本，例如empty_label='请选择课程'。

内容的提问来源于stack exchange，提问作者Peterkm