cannot cast type character varying[] to jsonb django migration

Question

I have alter my model from arrayfield to json field now i am receiving error

cannot cast type character varying[] to jsonb LINE 1: ...LUMN "questionaires" TYPE jsonb USING "questionaires"::jsonb.

How to fix this ? and how it did occur?

from

questionaires   = ArrayField(models.CharField(max_length=4000), null=True, blank=True)

to

questionaires   = JSONField(null = True,blank = True)

Answer 1

I think you have to perform multiple stage migrates:

1. Create temporary new field with type JSONField: Ex questionaires_2
2. Write custom python migration RunPython to convert data manually
3. Delete old field: questionaires
4. Rename temporary field to the old one questionaires_2 -> questionaires

More advance: refer to this https://stackoverflow.com/a/21997589/533738

Not tested!!!

ALTER TABLE <Your Table>
ALTER COLUMN questionaires TYPE JSONB
      USING translate(questionaires::text, '{}','[]')::JSONB;