如何在Django下拉菜单中只显示选项的子集

Question

我有一个应用程序，允许用户注册和注册课程(从"TrainingInstance"模型(。这些事件有名称等，在数据库中被分类为过去或当前(在"培训"模型中(。当我在模板中显示BuildOrderForm时，我只希望下拉菜单中显示当前培训的选项。如果没有javascript或Ajax，如何在Django中实现这一点？

我有以下表格.py：

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

以及models.py中的以下模型：

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('withdrawn', 'withdrawn'),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

Answer 1

以下是我所做的工作-这很有效，但我也愿意接受关于好/坏做法的反馈。

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

def __init__(self,*args,**kwargs):
super (BuildOrderForm,self ).__init__(*args,**kwargs)
self.fields['training_registered'].queryset = TrainingInstance.objects.filter(training__year ="current")