Django 模型属性不起作用 - Django

Question

我在尝试在 Django 模型中定义属性并访问它们时遇到了问题。我有 2 个模型，第一个是产品，第二个是产品属性。产品属性有几个字段，如颜色和品牌。我想创建属性来获取产品的品牌和颜色，以便在模板和过滤（django-filter）中使用，但模型中的属性没有按预期给出结果。请找到以下代码和备注供您参考和帮助。

产品型号：

class Product(models.Model):
measurement_choices = (('Liter', 'Liter'), ('Kilogram', 'Kilogram'), ('Cloth', 'Cloth'), ('Shoe', 'Shoe'))
name = models.CharField(max_length=200)
sku = models.CharField(max_length=30, null=True)
stock = models.CharField(max_length=10, null=True)
measurement = models.CharField(choices=measurement_choices, max_length=20, null=True)
description = models.CharField(max_length=10000)
price = models.DecimalField(max_digits=7, decimal_places=2)
discounted_price = models.DecimalField(max_digits=7, decimal_places=2, null=True, blank=True)
image = models.ImageField(upload_to='product/images', default='product.png', null=True, blank=True)
image_one = models.ImageField(upload_to='product/images', null=True, blank=True)
image_two = models.ImageField(upload_to='product/images', null=True, blank=True)
image_three = models.ImageField(upload_to='product/images', null=True, blank=True)
image_four = models.ImageField(upload_to='product/images', null=True, blank=True)
image_five = models.ImageField(upload_to='product/images', null=True, blank=True)
tags = models.ManyToManyField(Tags)
sub_category = models.ForeignKey(SubCategory, on_delete=models.SET_NULL, 
null=True,related_name='+')
status = models.CharField(max_length=20, choices=(('Active', 'Active'), ('Inactive', 
'Inactive')))
history = HistoricalRecords()

我为获得品牌名称而创建的属性：

def p_brand(self):
    brand = ''
    all_attributes = self.productattribute_set.all()
    for att in all_attributes:
        brand = att.brand.title
        print(brand)
    return brand 

此属性在视图中返回以下结果，而不是品牌名称：

   <bound method Product.p_brand of <Product: 1:T-Shirt:Men>>
   <bound method Product.p_brand of <Product: 2:Shoe:Men>>
   <bound method Product.p_brand of <Product: 3:Book:Men>>

产品属性模型：

class ProductAttribute(models.Model):
      product = models.ForeignKey(Product, on_delete=models.CASCADE)
      brand = models.ForeignKey(Brand, on_delete=models.CASCADE, null=True, 
      blank=True)
     color = models.ForeignKey(Color, on_delete=models.CASCADE, null=True, 
      blank=True)
      size = models.ForeignKey(Size, on_delete=models.CASCADE, null=True, blank=True)
      price = models.PositiveIntegerField(default=0)
      offer = models.ForeignKey(Offer, on_delete=models.CASCADE, null=True, 
      blank=True)
      image = models.ImageField(upload_to="product_imgs/", null=True, blank=True)
      history = HistoricalRecords()

我也尝试过使用下面的方法来获得品牌，效果很好。

for product in Product.objects.all():
    attr = product.productattribute_set.all()
    for att in attr:
    print(att.brand.title)

Answer 1

你没有让它成为一个属性，这是一个简单的方法。您需要添加@property decorator [Python-doc]：

class Product(models.Model):
    # …
    
    @property  # ← property decorator
    def p_brand(self):
        return ', '.join(
            pa.brand.title
            for pa in self.productattribute_set.select_related('brand')
        )