Django change database field from integer to CharField

I have a Django app with a populated (Postgres) database that has an integer field that I need to change to a CharField. I need to start storing data with leading zeros in this field. If I run migrate (Django 1.8.4), I get the following error:

psycopg2.ProgrammingError: operator does not exist: character varying >= integer

HINT: No operator matches the given name and argument type(s). You might need to add explicit type casts.

I tried searching Google, but didn’t really find much help. I don’t really know what I’m supposed to do here. Can anyone help?

Answer

Originally, I thought that there would be a simple solution where Django or Postgres would do the conversion automatically, but it appears that it doesn’t work that way. I think some of suggestions made by others might have worked, but I came up with a simple solution of my own. This was done on a production database so I had to be careful. I ended up adding the character field to the model and did the migration. I then ran a small script in the python shell that copied the data in the integer field, did the conversion that I needed, then wrote that to the new field in the same record in the production database.

for example:

members = Members.objects.all()
for mem in members:
    mem.memNumStr = str(mem.memNum)
    ... more data processing here
    mem.save()

So now, I had the data duplicated in the table in a str field and an int field. I could then modify the views that accessed that field and test it on the production database without breaking the old code. Once that is done, I can drop the old int field. A little bit involved, but pretty simple in the end.