How should I upgrade from bradjasper's django-jsonfield to Django's built-in jsonfield?

I have a Postgres 9.4 / Django 1.8 database that uses bradjasper's django-jsonfield package. (See https://github.com/bradjasper/django-jsonfield ) It works well, but I would like to upgrade the existing data to use Postgres 9.6 and Django 1.9's built-in JSONField. (See https://docs.djangoproject.com/en/1.10/ref/contrib/postgres/fields/#jsonfield ) This will allow more robust searches of JSON content.

How do I upgrade the old database to the new one?

What I've tried: I tried inserting a pair of schema migrations to

Convert the bradjasper JSONField to a TextField, including running the migration. (This shouldn't change the database, since bradjasper stores data as a string.)
Run Django's dumpdata command.
Updated Postgres & Django versions.
Run the migration to convert the TextField to Django's JSONField. (This should be a change in the database, from a text or json to jsonb.)
Run Django's loaddata command. This gives an error like: u"[] (type <type 'unicode'>) is not a valid list for field url_methods"]: (myapp.mytable:pk=1) field_value was '[]' I'm looking at postgresql migrating JSON to JSONB and Upgrade PostgreSQL JSON column to JSONB? but am hoping to minimize the custom SQL.

Solution

The ALTER COLUMN command from @tometzky via Upgrade PostgreSQL JSON column to JSONB? does this with surprisingly little hassle:

sudo -u postgres psql -c 'ALTER TABLE mytable ALTER COLUMN "myfield" TYPE jsonb USING "myfield"::text::jsonb;' mydatabase

I didn't need Django's loaddata / dumpdata commands or a custom migration.

I did have some issues getting pg_upgrade to work the way I wanted, since it wasn't on the default path and wanted to change the port used by Postgres during the upgrade. To get around that, I did the following:

pg_ctl -D /etc/postgresql/9.4/main/ stop
use sed on postgresql.conf to change which port it used
install Postgres 9.6
pg_ctl -D /etc/postgresql/9.6/main/ stop
cd /var/log/postgresql
run pg_upgrade
cd back to the original working directory
apt-get -y remove postgresql-9.4 postgresql-client-9.4 postgresql-server-dev-9.4
service postgresql start