How to copy an object from one model to another model - django

Question

Each user has many albums, and each album has its many photos. And each user has one set background image to hold its many images. Similarly, a user has one set of profile picture to hold its many images.
These are my models:
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)
Eg: I tried doing this: to let the user copy one image from ProfilePicture to Background Image, but didn't work:
# 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'
So my question is, how to copy an objects from one model to another? Any advice will be much appreciated.

Answer 1

You'll need to copy the properties of one object to another object. create is used when you want to create a new instance, not when you want to update a specific instance.
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()
Alternatively you can create a method on ProfilePicture if this is a common operation to contain this functionality.
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()
So you would just need to call m_pro_1.update(m_back_1) if we wanted to make m_pro_1 have the same properties as m_back_1
Also, if you wanted to create a new instance, I'd suggest using a classmethod like the following
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
This creates a new ProfilePicture and is used: profile_pic = ProfilePicture.create_from_bg(m_back_1)