Migrating ForeignKey to ManyToManyField raise ValueError("…they are not compatible types…")

[Adam Dobrawy]

I am unable to migrate ForeignKey to ManyToManyFields. I generated migrations by django-admin.py makemigratinons and I got error:
`
Applying bibliography.0013_auto_20141102_1346...Traceback (most recent call last):

File "X/bin/django-admin.py", line 5, in <module>

management.execute_from_command_line()

File "X/local/lib/python2.7/site-packages/django/core/management/init.py", line 385, in execute_from_command_line

utility.execute()

File "X/local/lib/python2.7/site-packages/django/core/management/init.py", line 377, in execute

self.fetch_command(subcommand).run_from_argv(self.argv)

File "X/local/lib/python2.7/site-packages/django/core/management/base.py", line 288, in run_from_argv

self.execute(*args, options.dict)

File "X/local/lib/python2.7/site-packages/django/core/management/base.py", line 338, in execute

output = self.handle(*args, options)

File "X/local/lib/python2.7/site-packages/django/core/management/commands/migrate.py", line 160, in handle

executor.migrate(targets, plan, fake=options.get("fake", False))

File "X/local/lib/python2.7/site-packages/django/db/migrations/executor.py", line 63, in migrate

self.apply_migration(migration, fake=fake)

File "X/local/lib/python2.7/site-packages/django/db/migrations/executor.py", line 97, in apply_migration

migration.apply(project_state, schema_editor)

File "X/local/lib/python2.7/site-packages/django/db/migrations/migration.py", line 107, in apply

operation.database_forwards(self.app_label, schema_editor, project_state, new_state)

File "X/local/lib/python2.7/site-packages/django/db/migrations/operations/fields.py", line 139, in database_forwards

schema_editor.alter_field(from_model, from_field, to_field)

File "X/local/lib/python2.7/site-packages/django/db/backends/schema.py", line 470, in alter_field

new_field,

ValueError: Cannot alter field bibliography.Publication.publisher into bibliography.Publication.publisher - they are not compatible types (you cannot alter to or from M2M fields, or add or remove through= on M2M fields)
`

I found workaround in few migrations, so...
.1. Create new fields ManyToManyFields in table (remember about related_name).
`

migrations.AddField(

model_name='publication',
name='publisher_many',
field=models.ManyToManyField(related_name='B', null=True, verbose_name='Publisher', to='bibliography.Publisher', blank=True),
preserve_default=True,

),
migrations.AddField(

model_name='publication',
name='publisher_org_many',
field=models.ManyToManyField(related_name='B', null=True, verbose_name='NGO-publisher', to='org_bank.Organization', blank=True),
preserve_default=True,

),

`
.2. Migrate data:
`
def move_to_many_fields(apps, schema_editor):

Publication = apps.get_model("bibliography", "Publication")
for obj in Publication.objects.filter(~Q(publisherisnull=True) | ~Q(publisher_orgisnull=True)).all():

obj.publisher_many = [obj.publisher]
obj.publisher_org_many = [obj.publisher_org]
obj.save()

…

migrations.RunPython(move_to_many_fields),

`
.3. Remove old-fields
`

migrations.RemoveField(

model_name='publication',
name='publisher',

),
migrations.RemoveField(

model_name='publication',
name='publisher_org',

),

`
.4. Rename new fields to old-fields name
`

migrations.RenameField(

model_name='publication',
old_name='publisher_many',
new_name='publisher',

),
migrations.RenameField(

model_name='publication',
old_name='publisher_org_many',
new_name='publisher_org',

),

`

What do you think about integration this kind migrations to Django?