现有对象Django上的OneTomany

我正在尝试更好地了解姜戈是如何工作的。使用下面的测试函数创建 类别、标签和项目 代表 MacBook Pro 然后添加一个 MacBook Pro 到那个类别、标签和项目(产品)。

相关型号: (注意,我正在进行故障排除,模型可能无法准确表示问题发生时的情况)

class Tag(models.Model):
    title = models.CharField(max_length=20)

    def __str__(self):
        return self.title

class Item(models.Model):
    name = models.CharField(max_length=100)
    description = models.CharField(max_length=100)
    manufacturer = models.ForeignKey('Manufacturer', blank=True, null=True, on_delete=models.SET_NULL)
    introduction = models.DateField(auto_now=True)
    quanity = models.IntegerField(default=0)
    is_retired = models.BooleanField(default=False)
    tags = models.ManyToManyField(Tag)

    def __str__(self):
        return self.name

    def add(self):
        pass

    def remove(self):
        pass

    def retire(self): # Rex came up with this, roll credits.
        pass 

    def count(self):
        pass

class OnHand(models.Model):
    name = models.CharField(max_length=100)
    serial = models.CharField(max_length=80)
    asset = models.CharField(max_length=20)
    product = models.ForeignKey(Item, blank=True, null=True, on_delete=models.CASCADE)


    def __str__(self):
        return self.serial

测试用例:

def make_macbook():
    """ Create a Manufacturer for Apple """
    apple = Manufacturer(name='Apple', rep_name='Jason Wilburn', support_number='1-800-Apple')
    apple.save()
    print('Manufacturer name: {}'.format(apple))

    """ Create a Category for Laptops """
    laptop = Category(name='Laptops')
    laptop.save()
    print('Category name: {}'.format(laptop))

    """ Create a Tag for Mac """
    mac = Tag(title='mac')
    mac.save()
    print('Tag name: {}'.format(mac))

    """ Create a MacBook Item """
    macbook = Item(name='Macbook Pro', description='15.5" Macbook Pro, 2018 Model', manufacturer=apple)
    macbook.save()
    print('Item name: {}'.format(macbook))

    """ Create a MacBook OnHand item """
    newMac = OnHand(name='MacBook Pro 15.5"', serial='SC02XP0NRJGH5', asset='DEPSC02XP0NRJGH5', product=macbook)
    newMac.save()


    return newMac.product

我现在测试的是添加新的 手头 对象到 类别、标签和项目 .

以下是我的资料:

def add_macbook():
    """ Find MacBook Item """
    macbook = Item.objects.filter(name='Macbook Pro')

    """ Create a MacBook OnHand item """
    newMac = OnHand(name='MacBook Pro 15.5"', serial='000000000000000', asset='DEP0000000000000', product=macbook)
    newMac.save()

我面临两个问题:

1. 类“item”没有“objects”成员
2. ValueError:无法分配“]>”:“OnHand.Product”必须是“item”实例。

我怎样才能得到现有的 项目 要关联的实例?

我也尝试过:

def add_macbook():
    """ Find MacBook Item """
    macbook = Item.objects.get(name='Macbook Pro')

    """ Create a MacBook OnHand item """
    newMac = OnHand(name='MacBook Pro 15.5"', serial='000000000000000', asset='DEP0000000000000')
    newMac.save()
    macbook.product.add(newMac)

这给了我明显的 “item”没有“product”属性 因为显然没有。我试过这个是因为 Tag 模型作品。