Description of problem:

During the migration from pulp2 to pulp3 on a Satellite 6.9.9 an error happens during the content-prepare phase while migrating RPMs, logging this traceback:
~~~
 "pulp_href": "/pulp/api/v3/tasks/e3ef9998-a19d-4def-8f69-305ffff669b3/",
            "pulp_created": "2022-05-27T17:08:43.443046Z",
            "state": "failed",
            "name": "pulp_2to3_migration.app.migration.complex_repo_migration",
            "started_at": "2022-05-27T17:19:30.170348Z",
            "finished_at": "2022-05-27T17:19:31.831923Z",
            "error": {
                "traceback": "  File "/usr/lib/python3.6/site-packages/rq/worker.py", line 936, in perform_job\n    rv = job.perform()\n  File "/usr/lib/python3.6/site-packages/rq/job.py", line 684, in perform\n    self._result = self._execute()\n  File "/usr/lib/python3.6/site-packages/rq/job.py", line 690, in _execute\n    return self.func(*self.args, **self.kwargs)\n  File "/usr/lib/python3.6/site-packages/pulp_2to3_migration/app/migration.py", line 201, in complex_repo_migration\n    create_repo_version(progress_rv, pulp2_repo, pulp3_remote)\n  File "/usr/lib/python3.6/site-packages/pulp_2to3_migration/app/migration.py", line 451, in create_repo_version\n    resolve_path_overlap(new_version)\n  File "/usr/lib/python3.6/site-packages/pulp_2to3_migration/app/migration.py", line 418, in resolve_path_overlap\n    version.remove_content(cas_with_conflicts[0].content)\n  File "/usr/lib/python3.6/site-packages/pulpcore/app/models/repository.py", line 618, in remove_content\n    if not content or not content.count():\n",
                "description": "'Content' object has no attribute 'count'"
~~~

Reformatting the traceback for readability:
~~~
"traceback": "  File "/usr/lib/python3.6/site-packages/rq/worker.py", line 936, in perform_job
    rv = job.perform()
  File "/usr/lib/python3.6/site-packages/rq/job.py", line 684, in perform
    self._result = self._execute()
  File "/usr/lib/python3.6/site-packages/rq/job.py", line 690, in _execute
    return self.func(*self.args, **self.kwargs)
  File "/usr/lib/python3.6/site-packages/pulp_2to3_migration/app/migration.py", line 201, in complex_repo_migration
    create_repo_version(progress_rv, pulp2_repo, pulp3_remote)
  File "/usr/lib/python3.6/site-packages/pulp_2to3_migration/app/migration.py", line 451, in create_repo_version
    resolve_path_overlap(new_version)
  File "/usr/lib/python3.6/site-packages/pulp_2to3_migration/app/migration.py", line 418, in resolve_path_overlap
    version.remove_content(cas_with_conflicts[0].content)
  File "/usr/lib/python3.6/site-packages/pulpcore/app/models/repository.py", line 618, in remove_content
    if not content or not content.count():",
                "description": "'Content' object has no attribute 'count'
~~~

Inspecting the use of content.count() in app/models/repository.py, we find out the Content class really doesn't implement a count() method, so this condition seems bound to fail every single time.
I wonder if content.count() here was intended as a test whether `content` is iterable, or maybe as a check that `content` contains more than 0 items (and is, by definition, iterable).


Assuming the former, I modified the test in app/models/repository.py, from:

    if not content or not content.count():

to:

    if not content or not hasattr(content, '__iter__'):


The modified code ran the migration successfully.

I don't know yet what would cause `content` to be iterable or not -- I suppose it could hold either a single Content object or a collection of Content objects.


Version-Release number of selected component (if applicable):
satellite-6.9.9-1.el7sat.noarch
python3-pulpcore-3.7.9-1.el7pc.noarch             
python3-pulp-2to3-migration-0.11.10-1.el7pc.noarch
python3-pulp-certguard-1.0.3-1.el7pc.noarch       
python3-pulp-container-2.1.2-1.el7pc.noarch       
python3-pulp-file-1.3.0-1.el7pc.noarch            
python3-pulp-rpm-3.11.4-1.el7pc.noarch            



How reproducible:
100% in this particular Satellite attempting a pulp-2to3 migration.

Steps to Reproduce:
1. Have a Satellite 6.9.9 with some particular (or not) contents.
2. Prepare contents for a pulp-2to3 migration for a Satellite upgrade: satellite-maintain content prepare

Actual results:
Some RPMs into the migration process, the traceback above printed as part of the pulp task failure.

Expected results:
The content prepare step works.

Additional info:

As an actual first step in the investigation I did for this support ticket, I simply removed the `not content.count()` condition and restarted the content prepare task, which failed at a different point with a traceback stating "content object is not iterable". So I assumed the `content.count()` condition was to check for iterability and went with my modified condition, `not hasattr(content, '__iter__')`, which in this particular case resolved the issue.