Rails - Jun 2013 - json text to text array migration questions

Hi, 

I have field in postgres (9.2.4) with type json.  The field looks like

       Column        |            Type             | Modifiers | Storage  | 
Stats target | Description 
---------------------+-----------------------------+-----------+----------+--------------+-------------
my_id_field           | json                        |           | extended 
|              | 

When I do " select my_id_field::json from table1", it returns
something like

 []
 []
 []
 ["abc"]
 []
 []
 []

I like to change this from type json to text[] and included the following 
in the migration

 execute "alter table table1 add column new_id_field text[] default 
''{}''::text[]"
 execute "UPDATE table1 SET new_id_field = [my_id_field] where my_id_field 
is not null"

I ended up with data like [["abc"]] and [[]], which was not what I
wanted

Questions:
1) how do I convert the json type to text[]?
2) in ActiveRecord, how do I select rows from table1 that are not []?

TIA
m

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