如何使用objects.create保存Django字段？

Question

我有一個模特：

class Certificate(models.Model):
    comments = models.TextField(blank=True, default='')
    generic_certificate = models.ForeignKey(GenericCertificate, related_name='certificates_awarded')
    tag = models.ForeignKey('Tag', related_name='certificates_awarded', null=True, blank=True)
    created_at = models.DateTimeField(auto_now_add=True)
    history_timestamp = models.DateTimeField(auto_now=True)
    rewardee = models.ForeignKey(OrganisationUser, related_name='certificates_rewarded')
    position =  models.CharField(max_length=50, default = '0,0')

我想保存給定主鍵的位置字段。

這是views.py：

def post(self, request , *args , **kwargs): 
        comments = Certificate.objects.values("comments").filter(pk = kwargs.get('cert_id') )
        gen_certi = Certificate.objects.values("generic_certificate").filter(pk = kwargs.get('cert_id') ) 
        tag = Certificate.objects.values("tag").filter(pk = kwargs.get('cert_id') )
        history_timestamp = Certificate.objects.values("history_timestamp").filter(pk = kwargs.get('cert_id') )
        rewardee = Certificate.objects.values("rewardee").filter(pk = kwargs.get('cert_id') )
        position = request.POST.get('hid')
        position = str([position])
        a = Certificate.objects.create( comments=comments, generic_certificate = gen_certi , tag=tag,rewardee=rewardee, position=position )
        print a

它給的錯誤：

Exception Value:    
Cannot assign "[{'generic_certificate': 2}]": "Certificate.generic_certificate" must be a "GenericCertificate" instance.

請幫助如何將位置字段保存到數據庫中。

Answer 1

gen_certi變量是一個查詢集（對象列表），因為您正在使用filter() -而是使用get() ：

gen_certi = Certificate.objects.get(pk = kwargs.get('cert_id')).generic_certificate

實際上，我不了解您打算在視圖中做什么。 如果要修改對象，則無需覆蓋現有字段，只需在request.POST更新傳遞給視圖的字段，例如position：

try:
    certificate = Certificate.objects.get(pk = kwargs.get('cert_id'))
    certificate.position = request.POST.get('hid')
    certificate.save()
except DoesNotExist: 
    # create new certificate
    certificate = Certificate()
    ...

希望能有所幫助。