Duplicate object in django, also duplicate child objects (related objects)

Question

I want to learn how to copy an object but also copy the object referencing to that object.

As an example (simplified): Model 1: version

id
name

Model 2: file

id
file name
file contents
foreign key pointing to version

Relationship: One version can have multiple files

So one software version can have multiple files. I want to duplicate a complete version. Currently I have the following:

def duplicate_version(request,id, MAC_address):
    new_version = Version.objects.get(pk=id)
    new_version.pk = None
    new_version.save()

    new_files = File.objects.get(version_id=id)  <-- here I get the error
    new_id = new_version.id
    new_files.version_id = new_id
    new_files.save()
    return get_all_versions(request, MAC_address)

I understand how to copy an object and change the id (=None). But how do I manage to duplicate all the related files?

Error I get: Exception Value: get() returned more than one File -- it returned 2!

May.D · Accepted Answer · 2018-05-21 10:43:09Z

4

First you should probably read this. The get() method returns only one object. What you need is the filter() method to get a queryset.

Second, as you will have a queryset you cant just do new_files.version_id = new_id. If your field is a foreign key, try something like below. If its a many to many, just do new_version.file_set.add(new_files):

def duplicate_version(request,id, MAC_address):
    new_version = Version.objects.get(pk=id)
    new_version.pk = None
    new_version = new_version.save()
    new_files = File.objects.filter(version_id=id)
    new_files.update(version_id=new_version.id)
    return get_all_versions(request, MAC_address)

edited May 21, 2018 at 10:43

answered May 20, 2018 at 21:53

May.D

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8 Comments

May.D Over a year ago

Then just use the update method like in the code I posted.

peter Over a year ago

@ Mehdi B Ok thank you. I added "new_files.save()" as is assume it is stil needed?

peter Over a year ago

queryset doesnt have a save method

May.D Over a year ago

Just use the sample code I posted. If you use update() you dont need save().Again, save is for a single object, like get()

peter Over a year ago

The code changed the foreign key of the new files. But it doesn't duplicate them

|

Maxim Kukhtenkov · Accepted Answer · 2018-05-21 21:53:46Z

3

def duplicate_version(request, pk, MAC_address):
    new_version = Version.objects.get(pk=pk)
    new_version.pk = None
    new_version.modification_date = datetime.datetime.now()
    new_version.save()

    new_files = File.objects.filter(version_id=pk)
    for file in new_files:
        file.version_id = new_version.pk
        file.pk = None
        file.save()
    return get_all_versions(request, MAC_address)

edited May 21, 2018 at 21:53

Maxim Kukhtenkov

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answered May 21, 2018 at 11:50

peter

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