in a rails migration, how can you remove the limit of a field

Question

Is it something like:

change_column :tablename, :fieldname, :limit => null

Answer 1

Strings without limit is not something most databases support: you have to specify size in varchar(SIZE) definition.
Although you could try, I would personally go with :limit => BIG_ENOUGH_NUMBER. You may also consider using CLOB type for very big texts.

Answer 2

To make it db-driver-independent one should write smth like this:

add_column :tablename, :fieldname_tmp, :text
Tablename.reset_column_information
Tablename.update_all("fieldname_tmp = fieldname")
remove_column :tablename, :fieldname
rename_column :tablename, :fieldname_tmp, :fieldname