如何将对象从一个模型复制到另一个模型

Question

每个用户都有很多 相册，每个相册都有很多 照片。每个用户都有一组 背景图片来保存它的许多图片。同样，用户有一组个人资料图片来保存其许多图像。

这些是我的模型：

class UserProfile(models.Model):
    user = models.OneToOneField(User)
    permanent_address = models.TextField()
    temporary_address = models.TextField()
    profile_pic = models.ForeignKey(ProfilePicture)
    background_pic = models.ForeignKey(BackgroundImage)


class Album(models.Model):
    user = models.ForeignKey(User)
    name = models.CharField(max_length=200)
    pub_date = models.DateTimeField(default=datetime.now)


class Photo(models.Model):
    album = models.ForeignKey(Album, default=3)
    image = models.ImageField(upload_to=get_upload_file_name)
    caption = models.CharField(max_length=200)
    pub_date = models.DateTimeField(default=datetime.now)


class BackgroundImage(models.Model):
    user = models.ForeignKey(User)
    image = models.ImageField(upload_to=get_upload_file_name)
    caption = models.CharField(max_length=200)
    pub_date = models.DateTimeField(default=datetime.now)


class ProfilePicture(models.Model):
    user = models.ForeignKey(User)
    image = models.ImageField(upload_to=get_upload_file_name)
    caption = models.CharField(max_length=200)
    pub_date = models.DateTimeField(default=datetime.now)

例如：我尝试这样做：让用户将 一个 图像 从 ProfilePicture 复制到 Background Image ，但没有用：

# Get the user
>>>m = User.objects.get(username='m')

# Get its set of Profile pictures
>>>m_pro_set = m.profilepicture_set.all()
>>>m_pro_set
[<ProfilePicture: pro_mik>]

# Get its set of Background images
>>>m_back_set = m.backgroundimage_set.all()
>>>m_back_set
[<BackgroundImage: bg_mik>]

# Get an image object from Profile picture of the user
>>>m_pro_1 = m.profilepicture_set.get(id=2)
>>>m_pro_1
<ProfilePicture: pro_mik>

# Get an image object from Background image of the user
>>>m_back_1 = m.backgroundimage_set.get(id=2)
>>>m_back_1
<BackgroundImage: bg_mik>

# So, I tried to copy one image from BackgroundImage of a user to ProfilePicture

>>>m_pro_set.objects.create(m_back_1)

    File "<console>", line 1, object has attribute 'objects'
AttributeError: 'QuerySet' object has no attribute 'objects'

所以我的问题是，如何将对象从一个模型复制到另一个模型？任何建议将不胜感激。

Answer 1

您需要将一个对象的属性复制到另一个对象。 create 在您想要创建新实例时使用，而不是在您想要更新特定实例时使用。

m_pro = m_pro_set[0] # m_pro_set is a list and need to get the specific instance
m_pro.image = m_back_1.image
m_pro.caption = m_back_1.caption
m_pro.pub_date = m_back_1.pub_date
m_pro.save()

如果这是包含此功能的常用操作，您也可以在 ProfilePicture 上创建一个方法。

class ProfilePicture(models.Model):
    user = models.ForeignKey(User)
    image = models.ImageField(upload_to=get_upload_file_name)
    caption = models.CharField(max_length=200)
    pub_date = models.DateTimeField(default=datetime.now)

    def update(self, bg_img):
        self.image = bg_img.image
        self.caption = bg_img.caption
        self.pub_date = bg_img.pub_date
        self.save()

因此，如果我们想让m_pro_1 具有与m_back_1 相同的属性，您只需调用m_pro_1.update(m_back_1)

另外，如果你想创建一个新实例，我建议使用classmethod，如下所示

class ProfilePicture(models.Model):
    ...

    @classmethod
    def create_from_bg(cls, bg_img):
        img = cls(user=bg_img.user, image=bg_img.image, caption=bg_img.caption, pub_date=bg_img.pub_date)
        img.save()
        return img

    @classmethod
    def create_from_photo(cls, photo):
        img = cls(user=photo.album.user, image=photo.image, caption=photo.caption, pub_date=photo.pub_date)
        img.save()
        return img

这会创建一个新的ProfilePicture 并使用：profile_pic = ProfilePicture.create_from_bg(m_back_1)