postgresql migrating JSON to JSONB [duplicate]

Question

In postgresql 9.4 the new JSONB was incorporated.

On a live DB in postgresql 9.3 I have a JSON column.

I want to migrate it to JSONB.

Assuming I migrated the DB first to 9.4 (using pg_upgrade). What do I do next?

Answer 1

ALTER TABLE table_with_json   ALTER COLUMN my_json   SET DATA TYPE jsonb   USING my_json::jsonb; 

Answer 2

In the context of Rails, here is an ActiveRecord migration alternative:

def change   reversible do |dir|     dir.up { change_column :models, :attribute, 'jsonb USING CAST(attribute AS jsonb)' }     dir.down { change_column :models, :attribute, 'json USING CAST(attribute AS json)' }   end end 

I don't know how this compares to the accepted answer performance-wise, but I tested this on a table with 120 000 records, each record having four json columns and it took me about a minute to migrate that table. Of course, I guess it depends on how complex the json structure is.

Also, notice that if your existing records have a default value of {}, you have to add to the above statements default: {}, because otherwise you'll have jsonb columns, but the default value will remain as '{}'::json.