setting :binary, :limit option on mysql column

How do I add a binary type column with limit option to a MySQL database
with migrations?

<snip />

Without a limit option! And even though it appears to migrate, the limit
in the application definitely does not change.

I use the limit option, and although it does not appear in my schema
file, it does change the size of the binary column. I haven't tested
to see if it creates an upper bound, but it does change the BLOB type.

The four BLOB types are TINYBLOB, BLOB, MEDIUMBLOB, and LONGBLOB.

For example, a :limit=>256.kilobyte creates a MEDIUMBLOB instead of a
BLOB (default).

If you want an upper bound on length, maybe create a validation in
your model?
http://api.rubyonrails.org/classes/ActiveRecord/Validations/ClassMethods.html#M000942

~Rusty